001/*
002 * Copyright (C) 2017 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.util.concurrent;
018
019import static com.google.common.base.Functions.constant;
020import static com.google.common.base.MoreObjects.toStringHelper;
021import static com.google.common.base.Preconditions.checkArgument;
022import static com.google.common.base.Preconditions.checkNotNull;
023import static com.google.common.base.Preconditions.checkState;
024import static com.google.common.collect.Lists.asList;
025import static com.google.common.util.concurrent.ClosingFuture.State.CLOSED;
026import static com.google.common.util.concurrent.ClosingFuture.State.CLOSING;
027import static com.google.common.util.concurrent.ClosingFuture.State.OPEN;
028import static com.google.common.util.concurrent.ClosingFuture.State.SUBSUMED;
029import static com.google.common.util.concurrent.ClosingFuture.State.WILL_CLOSE;
030import static com.google.common.util.concurrent.ClosingFuture.State.WILL_CREATE_VALUE_AND_CLOSER;
031import static com.google.common.util.concurrent.Futures.getDone;
032import static com.google.common.util.concurrent.Futures.immediateFuture;
033import static com.google.common.util.concurrent.Futures.nonCancellationPropagating;
034import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
035import static java.util.logging.Level.FINER;
036import static java.util.logging.Level.SEVERE;
037import static java.util.logging.Level.WARNING;
038
039import com.google.common.annotations.Beta;
040import com.google.common.annotations.VisibleForTesting;
041import com.google.common.base.Function;
042import com.google.common.collect.FluentIterable;
043import com.google.common.collect.ImmutableList;
044import com.google.common.util.concurrent.ClosingFuture.Combiner.AsyncCombiningCallable;
045import com.google.common.util.concurrent.ClosingFuture.Combiner.CombiningCallable;
046import com.google.common.util.concurrent.Futures.FutureCombiner;
047import com.google.errorprone.annotations.CanIgnoreReturnValue;
048import com.google.errorprone.annotations.DoNotMock;
049import com.google.j2objc.annotations.RetainedWith;
050import java.io.Closeable;
051import java.io.IOException;
052import java.util.IdentityHashMap;
053import java.util.Map;
054import java.util.concurrent.Callable;
055import java.util.concurrent.CancellationException;
056import java.util.concurrent.CountDownLatch;
057import java.util.concurrent.ExecutionException;
058import java.util.concurrent.Executor;
059import java.util.concurrent.Future;
060import java.util.concurrent.RejectedExecutionException;
061import java.util.concurrent.atomic.AtomicReference;
062import java.util.logging.Logger;
063import javax.annotation.CheckForNull;
064import org.checkerframework.checker.nullness.qual.Nullable;
065
066/**
067 * A step in a pipeline of an asynchronous computation. When the last step in the computation is
068 * complete, some objects captured during the computation are closed.
069 *
070 * <p>A pipeline of {@code ClosingFuture}s is a tree of steps. Each step represents either an
071 * asynchronously-computed intermediate value, or else an exception that indicates the failure or
072 * cancellation of the operation so far. The only way to extract the value or exception from a step
073 * is by declaring that step to be the last step of the pipeline. Nevertheless, we refer to the
074 * "value" of a successful step or the "result" (value or exception) of any step.
075 *
076 * <ol>
077 *   <li>A pipeline starts at its leaf step (or steps), which is created from either a callable
078 *       block or a {@link ListenableFuture}.
079 *   <li>Each other step is derived from one or more input steps. At each step, zero or more objects
080 *       can be captured for later closing.
081 *   <li>There is one last step (the root of the tree), from which you can extract the final result
082 *       of the computation. After that result is available (or the computation fails), all objects
083 *       captured by any of the steps in the pipeline are closed.
084 * </ol>
085 *
086 * <h3>Starting a pipeline</h3>
087 *
088 * Start a {@code ClosingFuture} pipeline {@linkplain #submit(ClosingCallable, Executor) from a
089 * callable block} that may capture objects for later closing. To start a pipeline from a {@link
090 * ListenableFuture} that doesn't create resources that should be closed later, you can use {@link
091 * #from(ListenableFuture)} instead.
092 *
093 * <h3>Derived steps</h3>
094 *
095 * A {@code ClosingFuture} step can be derived from one or more input {@code ClosingFuture} steps in
096 * ways similar to {@link FluentFuture}s:
097 *
098 * <ul>
099 *   <li>by transforming the value from a successful input step,
100 *   <li>by catching the exception from a failed input step, or
101 *   <li>by combining the results of several input steps.
102 * </ul>
103 *
104 * Each derivation can capture the next value or any intermediate objects for later closing.
105 *
106 * <p>A step can be the input to at most one derived step. Once you transform its value, catch its
107 * exception, or combine it with others, you cannot do anything else with it, including declare it
108 * to be the last step of the pipeline.
109 *
110 * <h4>Transforming</h4>
111 *
112 * To derive the next step by asynchronously applying a function to an input step's value, call
113 * {@link #transform(ClosingFunction, Executor)} or {@link #transformAsync(AsyncClosingFunction,
114 * Executor)} on the input step.
115 *
116 * <h4>Catching</h4>
117 *
118 * To derive the next step from a failed input step, call {@link #catching(Class, ClosingFunction,
119 * Executor)} or {@link #catchingAsync(Class, AsyncClosingFunction, Executor)} on the input step.
120 *
121 * <h4>Combining</h4>
122 *
123 * To derive a {@code ClosingFuture} from two or more input steps, pass the input steps to {@link
124 * #whenAllComplete(Iterable)} or {@link #whenAllSucceed(Iterable)} or its overloads.
125 *
126 * <h3>Cancelling</h3>
127 *
128 * Any step in a pipeline can be {@linkplain #cancel(boolean) cancelled}, even after another step
129 * has been derived, with the same semantics as cancelling a {@link Future}. In addition, a
130 * successfully cancelled step will immediately start closing all objects captured for later closing
131 * by it and by its input steps.
132 *
133 * <h3>Ending a pipeline</h3>
134 *
135 * Each {@code ClosingFuture} pipeline must be ended. To end a pipeline, decide whether you want to
136 * close the captured objects automatically or manually.
137 *
138 * <h4>Automatically closing</h4>
139 *
140 * You can extract a {@link Future} that represents the result of the last step in the pipeline by
141 * calling {@link #finishToFuture()}. All objects the pipeline has captured for closing will begin
142 * to be closed asynchronously <b>after</b> the returned {@code Future} is done: the future
143 * completes before closing starts, rather than once it has finished.
144 *
145 * <pre>{@code
146 * FluentFuture<UserName> userName =
147 *     ClosingFuture.submit(
148 *             closer -> closer.eventuallyClose(database.newTransaction(), closingExecutor),
149 *             executor)
150 *         .transformAsync((closer, transaction) -> transaction.queryClosingFuture("..."), executor)
151 *         .transform((closer, result) -> result.get("userName"), directExecutor())
152 *         .catching(DBException.class, e -> "no user", directExecutor())
153 *         .finishToFuture();
154 * }</pre>
155 *
156 * In this example, when the {@code userName} {@link Future} is done, the transaction and the query
157 * result cursor will both be closed, even if the operation is cancelled or fails.
158 *
159 * <h4>Manually closing</h4>
160 *
161 * If you want to close the captured objects manually, after you've used the final result, call
162 * {@link #finishToValueAndCloser(ValueAndCloserConsumer, Executor)} to get an object that holds the
163 * final result. You then call {@link ValueAndCloser#closeAsync()} to close the captured objects.
164 *
165 * <pre>{@code
166 *     ClosingFuture.submit(
167 *             closer -> closer.eventuallyClose(database.newTransaction(), closingExecutor),
168 *             executor)
169 *     .transformAsync((closer, transaction) -> transaction.queryClosingFuture("..."), executor)
170 *     .transform((closer, result) -> result.get("userName"), directExecutor())
171 *     .catching(DBException.class, e -> "no user", directExecutor())
172 *     .finishToValueAndCloser(
173 *         valueAndCloser -> this.userNameValueAndCloser = valueAndCloser, executor);
174 *
175 * // later
176 * try { // get() will throw if the operation failed or was cancelled.
177 *   UserName userName = userNameValueAndCloser.get();
178 *   // do something with userName
179 * } finally {
180 *   userNameValueAndCloser.closeAsync();
181 * }
182 * }</pre>
183 *
184 * In this example, when {@code userNameValueAndCloser.closeAsync()} is called, the transaction and
185 * the query result cursor will both be closed, even if the operation is cancelled or fails.
186 *
187 * <p>Note that if you don't call {@code closeAsync()}, the captured objects will not be closed. The
188 * automatic-closing approach described above is safer.
189 *
190 * @param <V> the type of the value of this step
191 * @since 30.0
192 */
193// TODO(dpb): Consider reusing one CloseableList for the entire pipeline, modulo combinations.
194@Beta // @Beta for one release.
195@DoNotMock("Use ClosingFuture.from(Futures.immediate*Future)")
196@ElementTypesAreNonnullByDefault
197// TODO(dpb): GWT compatibility.
198public final class ClosingFuture<V extends @Nullable Object> {
199
200  private static final Logger logger = Logger.getLogger(ClosingFuture.class.getName());
201
202  /**
203   * An object that can capture objects to be closed later, when a {@link ClosingFuture} pipeline is
204   * done.
205   */
206  public static final class DeferredCloser {
207    @RetainedWith private final CloseableList list;
208
209    DeferredCloser(CloseableList list) {
210      this.list = list;
211    }
212
213    /**
214     * Captures an object to be closed when a {@link ClosingFuture} pipeline is done.
215     *
216     * <p>For users of the {@code -jre} flavor of Guava, the object can be any {@code
217     * AutoCloseable}. For users of the {@code -android} flavor, the object must be a {@code
218     * Closeable}. (For more about the flavors, see <a
219     * href="https://github.com/google/guava#adding-guava-to-your-build">Adding Guava to your
220     * build</a>.)
221     *
222     * <p>Be careful when targeting an older SDK than you are building against (most commonly when
223     * building for Android): Ensure that any object you pass implements the interface not just in
224     * your current SDK version but also at the oldest version you support. For example, <a
225     * href="https://developer.android.com/sdk/api_diff/16/">API Level 16</a> is the first version
226     * in which {@code Cursor} is {@code Closeable}. To support older versions, pass a wrapper
227     * {@code Closeable} with a method reference like {@code cursor::close}.
228     *
229     * <p>Note that this method is still binary-compatible between flavors because the erasure of
230     * its parameter type is {@code Object}, not {@code AutoCloseable} or {@code Closeable}.
231     *
232     * @param closeable the object to be closed (see notes above)
233     * @param closingExecutor the object will be closed on this executor
234     * @return the first argument
235     */
236    @CanIgnoreReturnValue
237    @ParametricNullness
238    // TODO(b/163345357): Widen bound to AutoCloseable once we require API Level 19.
239    public <C extends @Nullable Object & @Nullable Closeable> C eventuallyClose(
240        @ParametricNullness C closeable, Executor closingExecutor) {
241      checkNotNull(closingExecutor);
242      if (closeable != null) {
243        list.add(closeable, closingExecutor);
244      }
245      return closeable;
246    }
247  }
248
249  /**
250   * An operation that computes a result.
251   *
252   * @param <V> the type of the result
253   */
254  public interface ClosingCallable<V extends @Nullable Object> {
255    /**
256     * Computes a result, or throws an exception if unable to do so.
257     *
258     * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable, Executor)
259     * closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline is done (but
260     * not before this method completes), even if this method throws or the pipeline is cancelled.
261     */
262    @ParametricNullness
263    V call(DeferredCloser closer) throws Exception;
264  }
265
266  /**
267   * An operation that computes a {@link ClosingFuture} of a result.
268   *
269   * @param <V> the type of the result
270   * @since 30.1
271   */
272  public interface AsyncClosingCallable<V extends @Nullable Object> {
273    /**
274     * Computes a result, or throws an exception if unable to do so.
275     *
276     * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable, Executor)
277     * closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline is done (but
278     * not before this method completes), even if this method throws or the pipeline is cancelled.
279     */
280    ClosingFuture<V> call(DeferredCloser closer) throws Exception;
281  }
282
283  /**
284   * A function from an input to a result.
285   *
286   * @param <T> the type of the input to the function
287   * @param <U> the type of the result of the function
288   */
289  public interface ClosingFunction<T extends @Nullable Object, U extends @Nullable Object> {
290
291    /**
292     * Applies this function to an input, or throws an exception if unable to do so.
293     *
294     * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable, Executor)
295     * closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline is done (but
296     * not before this method completes), even if this method throws or the pipeline is cancelled.
297     */
298    @ParametricNullness
299    U apply(DeferredCloser closer, @ParametricNullness T input) throws Exception;
300  }
301
302  /**
303   * A function from an input to a {@link ClosingFuture} of a result.
304   *
305   * @param <T> the type of the input to the function
306   * @param <U> the type of the result of the function
307   */
308  public interface AsyncClosingFunction<T extends @Nullable Object, U extends @Nullable Object> {
309    /**
310     * Applies this function to an input, or throws an exception if unable to do so.
311     *
312     * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable, Executor)
313     * closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline is done (but
314     * not before this method completes), even if this method throws or the pipeline is cancelled.
315     */
316    ClosingFuture<U> apply(DeferredCloser closer, @ParametricNullness T input) throws Exception;
317  }
318
319  /**
320   * An object that holds the final result of an asynchronous {@link ClosingFuture} operation and
321   * allows the user to close all the closeable objects that were captured during it for later
322   * closing.
323   *
324   * <p>The asynchronous operation will have completed before this object is created.
325   *
326   * @param <V> the type of the value of a successful operation
327   * @see ClosingFuture#finishToValueAndCloser(ValueAndCloserConsumer, Executor)
328   */
329  public static final class ValueAndCloser<V extends @Nullable Object> {
330
331    private final ClosingFuture<? extends V> closingFuture;
332
333    ValueAndCloser(ClosingFuture<? extends V> closingFuture) {
334      this.closingFuture = checkNotNull(closingFuture);
335    }
336
337    /**
338     * Returns the final value of the associated {@link ClosingFuture}, or throws an exception as
339     * {@link Future#get()} would.
340     *
341     * <p>Because the asynchronous operation has already completed, this method is synchronous and
342     * returns immediately.
343     *
344     * @throws CancellationException if the computation was cancelled
345     * @throws ExecutionException if the computation threw an exception
346     */
347    @ParametricNullness
348    public V get() throws ExecutionException {
349      return getDone(closingFuture.future);
350    }
351
352    /**
353     * Starts closing all closeable objects captured during the {@link ClosingFuture}'s asynchronous
354     * operation on the {@link Executor}s specified by calls to {@link
355     * DeferredCloser#eventuallyClose(Closeable, Executor)}.
356     *
357     * <p>If any such calls specified {@link MoreExecutors#directExecutor()}, those objects will be
358     * closed synchronously.
359     *
360     * <p>Idempotent: objects will be closed at most once.
361     */
362    public void closeAsync() {
363      closingFuture.close();
364    }
365  }
366
367  /**
368   * Represents an operation that accepts a {@link ValueAndCloser} for the last step in a {@link
369   * ClosingFuture} pipeline.
370   *
371   * @param <V> the type of the final value of a successful pipeline
372   * @see ClosingFuture#finishToValueAndCloser(ValueAndCloserConsumer, Executor)
373   */
374  public interface ValueAndCloserConsumer<V extends @Nullable Object> {
375
376    /** Accepts a {@link ValueAndCloser} for the last step in a {@link ClosingFuture} pipeline. */
377    void accept(ValueAndCloser<V> valueAndCloser);
378  }
379
380  /**
381   * Starts a {@link ClosingFuture} pipeline by submitting a callable block to an executor.
382   *
383   * @throws java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for
384   *     execution
385   */
386  public static <V extends @Nullable Object> ClosingFuture<V> submit(
387      ClosingCallable<V> callable, Executor executor) {
388    return new ClosingFuture<>(callable, executor);
389  }
390
391  /**
392   * Starts a {@link ClosingFuture} pipeline by submitting a callable block to an executor.
393   *
394   * @throws java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for
395   *     execution
396   * @since 30.1
397   */
398  public static <V extends @Nullable Object> ClosingFuture<V> submitAsync(
399      AsyncClosingCallable<V> callable, Executor executor) {
400    return new ClosingFuture<>(callable, executor);
401  }
402
403  /**
404   * Starts a {@link ClosingFuture} pipeline with a {@link ListenableFuture}.
405   *
406   * <p>{@code future}'s value will not be closed when the pipeline is done even if {@code V}
407   * implements {@link Closeable}. In order to start a pipeline with a value that will be closed
408   * when the pipeline is done, use {@link #submit(ClosingCallable, Executor)} instead.
409   */
410  public static <V extends @Nullable Object> ClosingFuture<V> from(ListenableFuture<V> future) {
411    return new ClosingFuture<V>(future);
412  }
413
414  /**
415   * Starts a {@link ClosingFuture} pipeline with a {@link ListenableFuture}.
416   *
417   * <p>If {@code future} succeeds, its value will be closed (using {@code closingExecutor)} when
418   * the pipeline is done, even if the pipeline is canceled or fails.
419   *
420   * <p>Cancelling the pipeline will not cancel {@code future}, so that the pipeline can access its
421   * value in order to close it.
422   *
423   * @param future the future to create the {@code ClosingFuture} from. For discussion of the
424   *     future's result type {@code C}, see {@link DeferredCloser#eventuallyClose(Closeable,
425   *     Executor)}.
426   * @param closingExecutor the future's result will be closed on this executor
427   * @deprecated Creating {@link Future}s of closeable types is dangerous in general because the
428   *     underlying value may never be closed if the {@link Future} is canceled after its operation
429   *     begins. Consider replacing code that creates {@link ListenableFuture}s of closeable types,
430   *     including those that pass them to this method, with {@link #submit(ClosingCallable,
431   *     Executor)} in order to ensure that resources do not leak. Or, to start a pipeline with a
432   *     {@link ListenableFuture} that doesn't create values that should be closed, use {@link
433   *     ClosingFuture#from}.
434   */
435  @Deprecated
436  // TODO(b/163345357): Widen bound to AutoCloseable once we require API Level 19.
437  public static <C extends @Nullable Object & @Nullable Closeable>
438      ClosingFuture<C> eventuallyClosing(
439          ListenableFuture<C> future, final Executor closingExecutor) {
440    checkNotNull(closingExecutor);
441    final ClosingFuture<C> closingFuture = new ClosingFuture<>(nonCancellationPropagating(future));
442    Futures.addCallback(
443        future,
444        new FutureCallback<@Nullable Closeable>() {
445          @Override
446          public void onSuccess(@CheckForNull Closeable result) {
447            closingFuture.closeables.closer.eventuallyClose(result, closingExecutor);
448          }
449
450          @Override
451          public void onFailure(Throwable t) {}
452        },
453        directExecutor());
454    return closingFuture;
455  }
456
457  /**
458   * Starts specifying how to combine {@link ClosingFuture}s into a single pipeline.
459   *
460   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
461   *     the {@code futures}, or if any has already been {@linkplain #finishToFuture() finished}
462   */
463  public static Combiner whenAllComplete(Iterable<? extends ClosingFuture<?>> futures) {
464    return new Combiner(false, futures);
465  }
466
467  /**
468   * Starts specifying how to combine {@link ClosingFuture}s into a single pipeline.
469   *
470   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
471   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
472   */
473  public static Combiner whenAllComplete(
474      ClosingFuture<?> future1, ClosingFuture<?>... moreFutures) {
475    return whenAllComplete(asList(future1, moreFutures));
476  }
477
478  /**
479   * Starts specifying how to combine {@link ClosingFuture}s into a single pipeline, assuming they
480   * all succeed. If any fail, the resulting pipeline will fail.
481   *
482   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
483   *     the {@code futures}, or if any has already been {@linkplain #finishToFuture() finished}
484   */
485  public static Combiner whenAllSucceed(Iterable<? extends ClosingFuture<?>> futures) {
486    return new Combiner(true, futures);
487  }
488
489  /**
490   * Starts specifying how to combine two {@link ClosingFuture}s into a single pipeline, assuming
491   * they all succeed. If any fail, the resulting pipeline will fail.
492   *
493   * <p>Calling this method allows you to use lambdas or method references typed with the types of
494   * the input {@link ClosingFuture}s.
495   *
496   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
497   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
498   */
499  public static <V1 extends @Nullable Object, V2 extends @Nullable Object>
500      Combiner2<V1, V2> whenAllSucceed(ClosingFuture<V1> future1, ClosingFuture<V2> future2) {
501    return new Combiner2<>(future1, future2);
502  }
503
504  /**
505   * Starts specifying how to combine three {@link ClosingFuture}s into a single pipeline, assuming
506   * they all succeed. If any fail, the resulting pipeline will fail.
507   *
508   * <p>Calling this method allows you to use lambdas or method references typed with the types of
509   * the input {@link ClosingFuture}s.
510   *
511   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
512   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
513   */
514  public static <
515          V1 extends @Nullable Object, V2 extends @Nullable Object, V3 extends @Nullable Object>
516      Combiner3<V1, V2, V3> whenAllSucceed(
517          ClosingFuture<V1> future1, ClosingFuture<V2> future2, ClosingFuture<V3> future3) {
518    return new Combiner3<>(future1, future2, future3);
519  }
520
521  /**
522   * Starts specifying how to combine four {@link ClosingFuture}s into a single pipeline, assuming
523   * they all succeed. If any fail, the resulting pipeline will fail.
524   *
525   * <p>Calling this method allows you to use lambdas or method references typed with the types of
526   * the input {@link ClosingFuture}s.
527   *
528   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
529   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
530   */
531  public static <
532          V1 extends @Nullable Object,
533          V2 extends @Nullable Object,
534          V3 extends @Nullable Object,
535          V4 extends @Nullable Object>
536      Combiner4<V1, V2, V3, V4> whenAllSucceed(
537          ClosingFuture<V1> future1,
538          ClosingFuture<V2> future2,
539          ClosingFuture<V3> future3,
540          ClosingFuture<V4> future4) {
541    return new Combiner4<>(future1, future2, future3, future4);
542  }
543
544  /**
545   * Starts specifying how to combine five {@link ClosingFuture}s into a single pipeline, assuming
546   * they all succeed. If any fail, the resulting pipeline will fail.
547   *
548   * <p>Calling this method allows you to use lambdas or method references typed with the types of
549   * the input {@link ClosingFuture}s.
550   *
551   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
552   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
553   */
554  public static <
555          V1 extends @Nullable Object,
556          V2 extends @Nullable Object,
557          V3 extends @Nullable Object,
558          V4 extends @Nullable Object,
559          V5 extends @Nullable Object>
560      Combiner5<V1, V2, V3, V4, V5> whenAllSucceed(
561          ClosingFuture<V1> future1,
562          ClosingFuture<V2> future2,
563          ClosingFuture<V3> future3,
564          ClosingFuture<V4> future4,
565          ClosingFuture<V5> future5) {
566    return new Combiner5<>(future1, future2, future3, future4, future5);
567  }
568
569  /**
570   * Starts specifying how to combine {@link ClosingFuture}s into a single pipeline, assuming they
571   * all succeed. If any fail, the resulting pipeline will fail.
572   *
573   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from any of
574   *     the arguments, or if any has already been {@linkplain #finishToFuture() finished}
575   */
576  public static Combiner whenAllSucceed(
577      ClosingFuture<?> future1,
578      ClosingFuture<?> future2,
579      ClosingFuture<?> future3,
580      ClosingFuture<?> future4,
581      ClosingFuture<?> future5,
582      ClosingFuture<?> future6,
583      ClosingFuture<?>... moreFutures) {
584    return whenAllSucceed(
585        FluentIterable.of(future1, future2, future3, future4, future5, future6)
586            .append(moreFutures));
587  }
588
589  private final AtomicReference<State> state = new AtomicReference<>(OPEN);
590  private final CloseableList closeables = new CloseableList();
591  private final FluentFuture<V> future;
592
593  private ClosingFuture(ListenableFuture<V> future) {
594    this.future = FluentFuture.from(future);
595  }
596
597  private ClosingFuture(final ClosingCallable<V> callable, Executor executor) {
598    checkNotNull(callable);
599    TrustedListenableFutureTask<V> task =
600        TrustedListenableFutureTask.create(
601            new Callable<V>() {
602              @Override
603              @ParametricNullness
604              public V call() throws Exception {
605                return callable.call(closeables.closer);
606              }
607
608              @Override
609              public String toString() {
610                return callable.toString();
611              }
612            });
613    executor.execute(task);
614    this.future = task;
615  }
616
617  private ClosingFuture(final AsyncClosingCallable<V> callable, Executor executor) {
618    checkNotNull(callable);
619    TrustedListenableFutureTask<V> task =
620        TrustedListenableFutureTask.create(
621            new AsyncCallable<V>() {
622              @Override
623              public ListenableFuture<V> call() throws Exception {
624                CloseableList newCloseables = new CloseableList();
625                try {
626                  ClosingFuture<V> closingFuture = callable.call(newCloseables.closer);
627                  closingFuture.becomeSubsumedInto(closeables);
628                  return closingFuture.future;
629                } finally {
630                  closeables.add(newCloseables, directExecutor());
631                }
632              }
633
634              @Override
635              public String toString() {
636                return callable.toString();
637              }
638            });
639    executor.execute(task);
640    this.future = task;
641  }
642
643  /**
644   * Returns a future that finishes when this step does. Calling {@code get()} on the returned
645   * future returns {@code null} if the step is successful or throws the same exception that would
646   * be thrown by calling {@code finishToFuture().get()} if this were the last step. Calling {@code
647   * cancel()} on the returned future has no effect on the {@code ClosingFuture} pipeline.
648   *
649   * <p>{@code statusFuture} differs from most methods on {@code ClosingFuture}: You can make calls
650   * to {@code statusFuture} <i>in addition to</i> the call you make to {@link #finishToFuture()} or
651   * a derivation method <i>on the same instance</i>. This is important because calling {@code
652   * statusFuture} alone does not provide a way to close the pipeline.
653   */
654  public ListenableFuture<?> statusFuture() {
655    return nonCancellationPropagating(future.transform(constant(null), directExecutor()));
656  }
657
658  /**
659   * Returns a new {@code ClosingFuture} pipeline step derived from this one by applying a function
660   * to its value. The function can use a {@link DeferredCloser} to capture objects to be closed
661   * when the pipeline is done.
662   *
663   * <p>If this {@code ClosingFuture} fails, the function will not be called, and the derived {@code
664   * ClosingFuture} will be equivalent to this one.
665   *
666   * <p>If the function throws an exception, that exception is used as the result of the derived
667   * {@code ClosingFuture}.
668   *
669   * <p>Example usage:
670   *
671   * <pre>{@code
672   * ClosingFuture<List<Row>> rowsFuture =
673   *     queryFuture.transform((closer, result) -> result.getRows(), executor);
674   * }</pre>
675   *
676   * <p>When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
677   * the discussion in the {@link ListenableFuture#addListener} documentation. All its warnings
678   * about heavyweight listeners are also applicable to heavyweight functions passed to this method.
679   *
680   * <p>After calling this method, you may not call {@link #finishToFuture()}, {@link
681   * #finishToValueAndCloser(ValueAndCloserConsumer, Executor)}, or any other derivation method on
682   * this {@code ClosingFuture}.
683   *
684   * @param function transforms the value of this step to the value of the derived step
685   * @param executor executor to run the function in
686   * @return the derived step
687   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from this
688   *     one, or if this {@code ClosingFuture} has already been {@linkplain #finishToFuture()
689   *     finished}
690   */
691  public <U extends @Nullable Object> ClosingFuture<U> transform(
692      final ClosingFunction<? super V, U> function, Executor executor) {
693    checkNotNull(function);
694    AsyncFunction<V, U> applyFunction =
695        new AsyncFunction<V, U>() {
696          @Override
697          public ListenableFuture<U> apply(V input) throws Exception {
698            return closeables.applyClosingFunction(function, input);
699          }
700
701          @Override
702          public String toString() {
703            return function.toString();
704          }
705        };
706    // TODO(dpb): Switch to future.transformSync when that exists (passing a throwing function).
707    return derive(future.transformAsync(applyFunction, executor));
708  }
709
710  /**
711   * Returns a new {@code ClosingFuture} pipeline step derived from this one by applying a function
712   * that returns a {@code ClosingFuture} to its value. The function can use a {@link
713   * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
714   * captured by the returned {@link ClosingFuture}).
715   *
716   * <p>If this {@code ClosingFuture} succeeds, the derived one will be equivalent to the one
717   * returned by the function.
718   *
719   * <p>If this {@code ClosingFuture} fails, the function will not be called, and the derived {@code
720   * ClosingFuture} will be equivalent to this one.
721   *
722   * <p>If the function throws an exception, that exception is used as the result of the derived
723   * {@code ClosingFuture}. But if the exception is thrown after the function creates a {@code
724   * ClosingFuture}, then none of the closeable objects in that {@code ClosingFuture} will be
725   * closed.
726   *
727   * <p>Usage guidelines for this method:
728   *
729   * <ul>
730   *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
731   *       {@code ClosingFuture}. If possible, prefer calling {@link #transform(ClosingFunction,
732   *       Executor)} instead, with a function that returns the next value directly.
733   *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor) closer.eventuallyClose()}
734   *       for every closeable object this step creates in order to capture it for later closing.
735   *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
736   *       ClosingFuture} call {@link #from(ListenableFuture)}.
737   *   <li>In case this step doesn't create new closeables, you can adapt an API that returns a
738   *       {@link ListenableFuture} to return a {@code ClosingFuture} by wrapping it with a call to
739   *       {@link #withoutCloser(AsyncFunction)}
740   * </ul>
741   *
742   * <p>Example usage:
743   *
744   * <pre>{@code
745   * // Result.getRowsClosingFuture() returns a ClosingFuture.
746   * ClosingFuture<List<Row>> rowsFuture =
747   *     queryFuture.transformAsync((closer, result) -> result.getRowsClosingFuture(), executor);
748   *
749   * // Result.writeRowsToOutputStreamFuture() returns a ListenableFuture that resolves to the
750   * // number of written rows. openOutputFile() returns a FileOutputStream (which implements
751   * // Closeable).
752   * ClosingFuture<Integer> rowsFuture2 =
753   *     queryFuture.transformAsync(
754   *         (closer, result) -> {
755   *           FileOutputStream fos = closer.eventuallyClose(openOutputFile(), closingExecutor);
756   *           return ClosingFuture.from(result.writeRowsToOutputStreamFuture(fos));
757   *      },
758   *      executor);
759   *
760   * // Result.getRowsFuture() returns a ListenableFuture (no new closeables are created).
761   * ClosingFuture<List<Row>> rowsFuture3 =
762   *     queryFuture.transformAsync(withoutCloser(Result::getRowsFuture), executor);
763   *
764   * }</pre>
765   *
766   * <p>When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
767   * the discussion in the {@link ListenableFuture#addListener} documentation. All its warnings
768   * about heavyweight listeners are also applicable to heavyweight functions passed to this method.
769   * (Specifically, {@code directExecutor} functions should avoid heavyweight operations inside
770   * {@code AsyncClosingFunction.apply}. Any heavyweight operations should occur in other threads
771   * responsible for completing the returned {@code ClosingFuture}.)
772   *
773   * <p>After calling this method, you may not call {@link #finishToFuture()}, {@link
774   * #finishToValueAndCloser(ValueAndCloserConsumer, Executor)}, or any other derivation method on
775   * this {@code ClosingFuture}.
776   *
777   * @param function transforms the value of this step to a {@code ClosingFuture} with the value of
778   *     the derived step
779   * @param executor executor to run the function in
780   * @return the derived step
781   * @throws IllegalStateException if a {@code ClosingFuture} has already been derived from this
782   *     one, or if this {@code ClosingFuture} has already been {@linkplain #finishToFuture()
783   *     finished}
784   */
785  public <U extends @Nullable Object> ClosingFuture<U> transformAsync(
786      final AsyncClosingFunction<? super V, U> function, Executor executor) {
787    checkNotNull(function);
788    AsyncFunction<V, U> applyFunction =
789        new AsyncFunction<V, U>() {
790          @Override
791          public ListenableFuture<U> apply(V input) throws Exception {
792            return closeables.applyAsyncClosingFunction(function, input);
793          }
794
795          @Override
796          public String toString() {
797            return function.toString();
798          }
799        };
800    return derive(future.transformAsync(applyFunction, executor));
801  }
802
803  /**
804   * Returns an {@link AsyncClosingFunction} that applies an {@link AsyncFunction} to an input,
805   * ignoring the DeferredCloser and returning a {@code ClosingFuture} derived from the returned
806   * {@link ListenableFuture}.
807   *
808   * <p>Use this method to pass a transformation to {@link #transformAsync(AsyncClosingFunction,
809   * Executor)} or to {@link #catchingAsync(Class, AsyncClosingFunction, Executor)} as long as it
810   * meets these conditions:
811   *
812   * <ul>
813   *   <li>It does not need to capture any {@link Closeable} objects by calling {@link
814   *       DeferredCloser#eventuallyClose(Closeable, Executor)}.
815   *   <li>It returns a {@link ListenableFuture}.
816   * </ul>
817   *
818   * <p>Example usage:
819   *
820   * <pre>{@code
821   * // Result.getRowsFuture() returns a ListenableFuture.
822   * ClosingFuture<List<Row>> rowsFuture =
823   *     queryFuture.transformAsync(withoutCloser(Result::getRowsFuture), executor);
824   * }</pre>
825   *
826   * @param function transforms the value of a {@code ClosingFuture} step to a {@link
827   *     ListenableFuture} with the value of a derived step
828   */
829  public static <V extends @Nullable Object, U extends @Nullable Object>
830      AsyncClosingFunction<V, U> withoutCloser(final AsyncFunction<V, U> function) {
831    checkNotNull(function);
832    return new AsyncClosingFunction<V, U>() {
833      @Override
834      public ClosingFuture<U> apply(DeferredCloser closer, V input) throws Exception {
835        return ClosingFuture.from(function.apply(input));
836      }
837    };
838  }
839
840  /**
841   * Returns a new {@code ClosingFuture} pipeline step derived from this one by applying a function
842   * to its exception if it is an instance of a given exception type. The function can use a {@link
843   * DeferredCloser} to capture objects to be closed when the pipeline is done.
844   *
845   * <p>If this {@code ClosingFuture} succeeds or fails with a different exception type, the
846   * function will not be called, and the derived {@code ClosingFuture} will be equivalent to this
847   * one.
848   *
849   * <p>If the function throws an exception, that exception is used as the result of the derived
850   * {@code ClosingFuture}.
851   *
852   * <p>Example usage:
853   *
854   * <pre>{@code
855   * ClosingFuture<QueryResult> queryFuture =
856   *     queryFuture.catching(
857   *         QueryException.class, (closer, x) -> Query.emptyQueryResult(), executor);
858   * }</pre>
859   *
860   * <p>When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
861   * the discussion in the {@link ListenableFuture#addListener} documentation. All its warnings
862   * about heavyweight listeners are also applicable to heavyweight functions passed to this method.
863   *
864   * <p>After calling this method, you may not call {@link #finishToFuture()}, {@link
865   * #finishToValueAndCloser(ValueAndCloserConsumer, Executor)}, or any other derivation method on
866   * this {@code ClosingFuture}.
867   *
868   * @param exceptionType the exception type that triggers use of {@code fallback}. The exception
869   *     type is matched against this step's exception. "This step's exception" means the cause of
870   *     the {@link ExecutionException} thrown by {@link Future#get()} on the {@link Future}
871   *     underlying this step or, if {@code get()} throws a different kind of exception, that
872   *     exception itself. To avoid hiding bugs and other unrecoverable errors, callers should
873   *     prefer more specific types, avoiding {@code Throwable.class} in particular.
874   * @param fallback the function to be called if this step fails with the expected exception type.
875   *     The function's argument is this step's exception. "This step's exception" means the cause
876   *     of the {@link ExecutionException} thrown by {@link Future#get()} on the {@link Future}
877   *     underlying this step or, if {@code get()} throws a different kind of exception, that
878   *     exception itself.
879   * @param executor the executor that runs {@code fallback} if the input fails
880   */
881  public <X extends Throwable> ClosingFuture<V> catching(
882      Class<X> exceptionType, ClosingFunction<? super X, ? extends V> fallback, Executor executor) {
883    return catchingMoreGeneric(exceptionType, fallback, executor);
884  }
885
886  // Avoids generic type capture inconsistency problems where |? extends V| is incompatible with V.
887  private <X extends Throwable, W extends V> ClosingFuture<V> catchingMoreGeneric(
888      Class<X> exceptionType, final ClosingFunction<? super X, W> fallback, Executor executor) {
889    checkNotNull(fallback);
890    AsyncFunction<X, W> applyFallback =
891        new AsyncFunction<X, W>() {
892          @Override
893          public ListenableFuture<W> apply(X exception) throws Exception {
894            return closeables.applyClosingFunction(fallback, exception);
895          }
896
897          @Override
898          public String toString() {
899            return fallback.toString();
900          }
901        };
902    // TODO(dpb): Switch to future.catchingSync when that exists (passing a throwing function).
903    return derive(future.catchingAsync(exceptionType, applyFallback, executor));
904  }
905
906  /**
907   * Returns a new {@code ClosingFuture} pipeline step derived from this one by applying a function
908   * that returns a {@code ClosingFuture} to its exception if it is an instance of a given exception
909   * type. The function can use a {@link DeferredCloser} to capture objects to be closed when the
910   * pipeline is done (other than those captured by the returned {@link ClosingFuture}).
911   *
912   * <p>If this {@code ClosingFuture} fails with an exception of the given type, the derived {@code
913   * ClosingFuture} will be equivalent to the one returned by the function.
914   *
915   * <p>If this {@code ClosingFuture} succeeds or fails with a different exception type, the
916   * function will not be called, and the derived {@code ClosingFuture} will be equivalent to this
917   * one.
918   *
919   * <p>If the function throws an exception, that exception is used as the result of the derived
920   * {@code ClosingFuture}. But if the exception is thrown after the function creates a {@code
921   * ClosingFuture}, then none of the closeable objects in that {@code ClosingFuture} will be
922   * closed.
923   *
924   * <p>Usage guidelines for this method:
925   *
926   * <ul>
927   *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
928   *       {@code ClosingFuture}. If possible, prefer calling {@link #catching(Class,
929   *       ClosingFunction, Executor)} instead, with a function that returns the next value
930   *       directly.
931   *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor) closer.eventuallyClose()}
932   *       for every closeable object this step creates in order to capture it for later closing.
933   *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
934   *       ClosingFuture} call {@link #from(ListenableFuture)}.
935   *   <li>In case this step doesn't create new closeables, you can adapt an API that returns a
936   *       {@link ListenableFuture} to return a {@code ClosingFuture} by wrapping it with a call to
937   *       {@link #withoutCloser(AsyncFunction)}
938   * </ul>
939   *
940   * <p>Example usage:
941   *
942   * <pre>{@code
943   * // Fall back to a secondary input stream in case of IOException.
944   * ClosingFuture<InputStream> inputFuture =
945   *     firstInputFuture.catchingAsync(
946   *         IOException.class, (closer, x) -> secondaryInputStreamClosingFuture(), executor);
947   * }
948   * }</pre>
949   *
950   * <p>When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
951   * the discussion in the {@link ListenableFuture#addListener} documentation. All its warnings
952   * about heavyweight listeners are also applicable to heavyweight functions passed to this method.
953   * (Specifically, {@code directExecutor} functions should avoid heavyweight operations inside
954   * {@code AsyncClosingFunction.apply}. Any heavyweight operations should occur in other threads
955   * responsible for completing the returned {@code ClosingFuture}.)
956   *
957   * <p>After calling this method, you may not call {@link #finishToFuture()}, {@link
958   * #finishToValueAndCloser(ValueAndCloserConsumer, Executor)}, or any other derivation method on
959   * this {@code ClosingFuture}.
960   *
961   * @param exceptionType the exception type that triggers use of {@code fallback}. The exception
962   *     type is matched against this step's exception. "This step's exception" means the cause of
963   *     the {@link ExecutionException} thrown by {@link Future#get()} on the {@link Future}
964   *     underlying this step or, if {@code get()} throws a different kind of exception, that
965   *     exception itself. To avoid hiding bugs and other unrecoverable errors, callers should
966   *     prefer more specific types, avoiding {@code Throwable.class} in particular.
967   * @param fallback the function to be called if this step fails with the expected exception type.
968   *     The function's argument is this step's exception. "This step's exception" means the cause
969   *     of the {@link ExecutionException} thrown by {@link Future#get()} on the {@link Future}
970   *     underlying this step or, if {@code get()} throws a different kind of exception, that
971   *     exception itself.
972   * @param executor the executor that runs {@code fallback} if the input fails
973   */
974  // TODO(dpb): Should this do something special if the function throws CancellationException or
975  // ExecutionException?
976  public <X extends Throwable> ClosingFuture<V> catchingAsync(
977      Class<X> exceptionType,
978      AsyncClosingFunction<? super X, ? extends V> fallback,
979      Executor executor) {
980    return catchingAsyncMoreGeneric(exceptionType, fallback, executor);
981  }
982
983  // Avoids generic type capture inconsistency problems where |? extends V| is incompatible with V.
984  private <X extends Throwable, W extends V> ClosingFuture<V> catchingAsyncMoreGeneric(
985      Class<X> exceptionType,
986      final AsyncClosingFunction<? super X, W> fallback,
987      Executor executor) {
988    checkNotNull(fallback);
989    AsyncFunction<X, W> asyncFunction =
990        new AsyncFunction<X, W>() {
991          @Override
992          public ListenableFuture<W> apply(X exception) throws Exception {
993            return closeables.applyAsyncClosingFunction(fallback, exception);
994          }
995
996          @Override
997          public String toString() {
998            return fallback.toString();
999          }
1000        };
1001    return derive(future.catchingAsync(exceptionType, asyncFunction, executor));
1002  }
1003
1004  /**
1005   * Marks this step as the last step in the {@code ClosingFuture} pipeline.
1006   *
1007   * <p>The returned {@link Future} is completed when the pipeline's computation completes, or when
1008   * the pipeline is cancelled.
1009   *
1010   * <p>All objects the pipeline has captured for closing will begin to be closed asynchronously
1011   * <b>after</b> the returned {@code Future} is done: the future completes before closing starts,
1012   * rather than once it has finished.
1013   *
1014   * <p>After calling this method, you may not call {@link
1015   * #finishToValueAndCloser(ValueAndCloserConsumer, Executor)}, this method, or any other
1016   * derivation method on this {@code ClosingFuture}.
1017   *
1018   * @return a {@link Future} that represents the final value or exception of the pipeline
1019   */
1020  public FluentFuture<V> finishToFuture() {
1021    if (compareAndUpdateState(OPEN, WILL_CLOSE)) {
1022      logger.log(FINER, "will close {0}", this);
1023      future.addListener(
1024          new Runnable() {
1025            @Override
1026            public void run() {
1027              checkAndUpdateState(WILL_CLOSE, CLOSING);
1028              close();
1029              checkAndUpdateState(CLOSING, CLOSED);
1030            }
1031          },
1032          directExecutor());
1033    } else {
1034      switch (state.get()) {
1035        case SUBSUMED:
1036          throw new IllegalStateException(
1037              "Cannot call finishToFuture() after deriving another step");
1038
1039        case WILL_CREATE_VALUE_AND_CLOSER:
1040          throw new IllegalStateException(
1041              "Cannot call finishToFuture() after calling finishToValueAndCloser()");
1042
1043        case WILL_CLOSE:
1044        case CLOSING:
1045        case CLOSED:
1046          throw new IllegalStateException("Cannot call finishToFuture() twice");
1047
1048        case OPEN:
1049          throw new AssertionError();
1050      }
1051    }
1052    return future;
1053  }
1054
1055  /**
1056   * Marks this step as the last step in the {@code ClosingFuture} pipeline. When this step is done,
1057   * {@code receiver} will be called with an object that contains the result of the operation. The
1058   * receiver can store the {@link ValueAndCloser} outside the receiver for later synchronous use.
1059   *
1060   * <p>After calling this method, you may not call {@link #finishToFuture()}, this method again, or
1061   * any other derivation method on this {@code ClosingFuture}.
1062   *
1063   * @param consumer a callback whose method will be called (using {@code executor}) when this
1064   *     operation is done
1065   */
1066  public void finishToValueAndCloser(
1067      final ValueAndCloserConsumer<? super V> consumer, Executor executor) {
1068    checkNotNull(consumer);
1069    if (!compareAndUpdateState(OPEN, WILL_CREATE_VALUE_AND_CLOSER)) {
1070      switch (state.get()) {
1071        case SUBSUMED:
1072          throw new IllegalStateException(
1073              "Cannot call finishToValueAndCloser() after deriving another step");
1074
1075        case WILL_CLOSE:
1076        case CLOSING:
1077        case CLOSED:
1078          throw new IllegalStateException(
1079              "Cannot call finishToValueAndCloser() after calling finishToFuture()");
1080
1081        case WILL_CREATE_VALUE_AND_CLOSER:
1082          throw new IllegalStateException("Cannot call finishToValueAndCloser() twice");
1083
1084        case OPEN:
1085          break;
1086      }
1087      throw new AssertionError(state);
1088    }
1089    future.addListener(
1090        new Runnable() {
1091          @Override
1092          public void run() {
1093            provideValueAndCloser(consumer, ClosingFuture.this);
1094          }
1095        },
1096        executor);
1097  }
1098
1099  private static <C extends @Nullable Object, V extends C> void provideValueAndCloser(
1100      ValueAndCloserConsumer<C> consumer, ClosingFuture<V> closingFuture) {
1101    consumer.accept(new ValueAndCloser<C>(closingFuture));
1102  }
1103
1104  /**
1105   * Attempts to cancel execution of this step. This attempt will fail if the step has already
1106   * completed, has already been cancelled, or could not be cancelled for some other reason. If
1107   * successful, and this step has not started when {@code cancel} is called, this step should never
1108   * run.
1109   *
1110   * <p>If successful, causes the objects captured by this step (if already started) and its input
1111   * step(s) for later closing to be closed on their respective {@link Executor}s. If any such calls
1112   * specified {@link MoreExecutors#directExecutor()}, those objects will be closed synchronously.
1113   *
1114   * @param mayInterruptIfRunning {@code true} if the thread executing this task should be
1115   *     interrupted; otherwise, in-progress tasks are allowed to complete, but the step will be
1116   *     cancelled regardless
1117   * @return {@code false} if the step could not be cancelled, typically because it has already
1118   *     completed normally; {@code true} otherwise
1119   */
1120  @CanIgnoreReturnValue
1121  public boolean cancel(boolean mayInterruptIfRunning) {
1122    logger.log(FINER, "cancelling {0}", this);
1123    boolean cancelled = future.cancel(mayInterruptIfRunning);
1124    if (cancelled) {
1125      close();
1126    }
1127    return cancelled;
1128  }
1129
1130  private void close() {
1131    logger.log(FINER, "closing {0}", this);
1132    closeables.close();
1133  }
1134
1135  private <U extends @Nullable Object> ClosingFuture<U> derive(FluentFuture<U> future) {
1136    ClosingFuture<U> derived = new ClosingFuture<>(future);
1137    becomeSubsumedInto(derived.closeables);
1138    return derived;
1139  }
1140
1141  private void becomeSubsumedInto(CloseableList otherCloseables) {
1142    checkAndUpdateState(OPEN, SUBSUMED);
1143    otherCloseables.add(closeables, directExecutor());
1144  }
1145
1146  /**
1147   * An object that can return the value of the {@link ClosingFuture}s that are passed to {@link
1148   * #whenAllComplete(Iterable)} or {@link #whenAllSucceed(Iterable)}.
1149   *
1150   * <p>Only for use by a {@link CombiningCallable} or {@link AsyncCombiningCallable} object.
1151   */
1152  public static final class Peeker {
1153    private final ImmutableList<ClosingFuture<?>> futures;
1154    private volatile boolean beingCalled;
1155
1156    private Peeker(ImmutableList<ClosingFuture<?>> futures) {
1157      this.futures = checkNotNull(futures);
1158    }
1159
1160    /**
1161     * Returns the value of {@code closingFuture}.
1162     *
1163     * @throws ExecutionException if {@code closingFuture} is a failed step
1164     * @throws CancellationException if the {@code closingFuture}'s future was cancelled
1165     * @throws IllegalArgumentException if {@code closingFuture} is not one of the futures passed to
1166     *     {@link #whenAllComplete(Iterable)} or {@link #whenAllComplete(Iterable)}
1167     * @throws IllegalStateException if called outside of a call to {@link
1168     *     CombiningCallable#call(DeferredCloser, Peeker)} or {@link
1169     *     AsyncCombiningCallable#call(DeferredCloser, Peeker)}
1170     */
1171    @ParametricNullness
1172    public final <D extends @Nullable Object> D getDone(ClosingFuture<D> closingFuture)
1173        throws ExecutionException {
1174      checkState(beingCalled);
1175      checkArgument(futures.contains(closingFuture));
1176      return Futures.getDone(closingFuture.future);
1177    }
1178
1179    @ParametricNullness
1180    private <V extends @Nullable Object> V call(
1181        CombiningCallable<V> combiner, CloseableList closeables) throws Exception {
1182      beingCalled = true;
1183      CloseableList newCloseables = new CloseableList();
1184      try {
1185        return combiner.call(newCloseables.closer, this);
1186      } finally {
1187        closeables.add(newCloseables, directExecutor());
1188        beingCalled = false;
1189      }
1190    }
1191
1192    private <V extends @Nullable Object> FluentFuture<V> callAsync(
1193        AsyncCombiningCallable<V> combiner, CloseableList closeables) throws Exception {
1194      beingCalled = true;
1195      CloseableList newCloseables = new CloseableList();
1196      try {
1197        ClosingFuture<V> closingFuture = combiner.call(newCloseables.closer, this);
1198        closingFuture.becomeSubsumedInto(closeables);
1199        return closingFuture.future;
1200      } finally {
1201        closeables.add(newCloseables, directExecutor());
1202        beingCalled = false;
1203      }
1204    }
1205  }
1206
1207  /**
1208   * A builder of a {@link ClosingFuture} step that is derived from more than one input step.
1209   *
1210   * <p>See {@link #whenAllComplete(Iterable)} and {@link #whenAllSucceed(Iterable)} for how to
1211   * instantiate this class.
1212   *
1213   * <p>Example:
1214   *
1215   * <pre>{@code
1216   * final ClosingFuture<BufferedReader> file1ReaderFuture = ...;
1217   * final ClosingFuture<BufferedReader> file2ReaderFuture = ...;
1218   * ListenableFuture<Integer> numberOfDifferentLines =
1219   *       ClosingFuture.whenAllSucceed(file1ReaderFuture, file2ReaderFuture)
1220   *           .call(
1221   *               (closer, peeker) -> {
1222   *                 BufferedReader file1Reader = peeker.getDone(file1ReaderFuture);
1223   *                 BufferedReader file2Reader = peeker.getDone(file2ReaderFuture);
1224   *                 return countDifferentLines(file1Reader, file2Reader);
1225   *               },
1226   *               executor)
1227   *           .closing(executor);
1228   * }</pre>
1229   */
1230  // TODO(cpovirk): Use simple name instead of fully qualified after we stop building with JDK 8.
1231  @com.google.errorprone.annotations.DoNotMock(
1232      "Use ClosingFuture.whenAllSucceed() or .whenAllComplete() instead.")
1233  public static class Combiner {
1234
1235    private final CloseableList closeables = new CloseableList();
1236
1237    /**
1238     * An operation that returns a result and may throw an exception.
1239     *
1240     * @param <V> the type of the result
1241     */
1242    public interface CombiningCallable<V extends @Nullable Object> {
1243      /**
1244       * Computes a result, or throws an exception if unable to do so.
1245       *
1246       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1247       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1248       * is done (but not before this method completes), even if this method throws or the pipeline
1249       * is cancelled.
1250       *
1251       * @param peeker used to get the value of any of the input futures
1252       */
1253      @ParametricNullness
1254      V call(DeferredCloser closer, Peeker peeker) throws Exception;
1255    }
1256
1257    /**
1258     * An operation that returns a {@link ClosingFuture} result and may throw an exception.
1259     *
1260     * @param <V> the type of the result
1261     */
1262    public interface AsyncCombiningCallable<V extends @Nullable Object> {
1263      /**
1264       * Computes a {@link ClosingFuture} result, or throws an exception if unable to do so.
1265       *
1266       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1267       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1268       * is done (but not before this method completes), even if this method throws or the pipeline
1269       * is cancelled.
1270       *
1271       * @param peeker used to get the value of any of the input futures
1272       */
1273      ClosingFuture<V> call(DeferredCloser closer, Peeker peeker) throws Exception;
1274    }
1275
1276    private final boolean allMustSucceed;
1277    protected final ImmutableList<ClosingFuture<?>> inputs;
1278
1279    private Combiner(boolean allMustSucceed, Iterable<? extends ClosingFuture<?>> inputs) {
1280      this.allMustSucceed = allMustSucceed;
1281      this.inputs = ImmutableList.copyOf(inputs);
1282      for (ClosingFuture<?> input : inputs) {
1283        input.becomeSubsumedInto(closeables);
1284      }
1285    }
1286
1287    /**
1288     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1289     * combining function to their values. The function can use a {@link DeferredCloser} to capture
1290     * objects to be closed when the pipeline is done.
1291     *
1292     * <p>If this combiner was returned by a {@link #whenAllSucceed} method and any of the inputs
1293     * fail, so will the returned step.
1294     *
1295     * <p>If the combiningCallable throws a {@code CancellationException}, the pipeline will be
1296     * cancelled.
1297     *
1298     * <p>If the combiningCallable throws an {@code ExecutionException}, the cause of the thrown
1299     * {@code ExecutionException} will be extracted and used as the failure of the derived step.
1300     */
1301    public <V extends @Nullable Object> ClosingFuture<V> call(
1302        final CombiningCallable<V> combiningCallable, Executor executor) {
1303      Callable<V> callable =
1304          new Callable<V>() {
1305            @Override
1306            @ParametricNullness
1307            public V call() throws Exception {
1308              return new Peeker(inputs).call(combiningCallable, closeables);
1309            }
1310
1311            @Override
1312            public String toString() {
1313              return combiningCallable.toString();
1314            }
1315          };
1316      ClosingFuture<V> derived = new ClosingFuture<>(futureCombiner().call(callable, executor));
1317      derived.closeables.add(closeables, directExecutor());
1318      return derived;
1319    }
1320
1321    /**
1322     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1323     * {@code ClosingFuture}-returning function to their values. The function can use a {@link
1324     * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
1325     * captured by the returned {@link ClosingFuture}).
1326     *
1327     * <p>If this combiner was returned by a {@link #whenAllSucceed} method and any of the inputs
1328     * fail, so will the returned step.
1329     *
1330     * <p>If the combiningCallable throws a {@code CancellationException}, the pipeline will be
1331     * cancelled.
1332     *
1333     * <p>If the combiningCallable throws an {@code ExecutionException}, the cause of the thrown
1334     * {@code ExecutionException} will be extracted and used as the failure of the derived step.
1335     *
1336     * <p>If the combiningCallable throws any other exception, it will be used as the failure of the
1337     * derived step.
1338     *
1339     * <p>If an exception is thrown after the combiningCallable creates a {@code ClosingFuture},
1340     * then none of the closeable objects in that {@code ClosingFuture} will be closed.
1341     *
1342     * <p>Usage guidelines for this method:
1343     *
1344     * <ul>
1345     *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
1346     *       {@code ClosingFuture}. If possible, prefer calling {@link #call(CombiningCallable,
1347     *       Executor)} instead, with a function that returns the next value directly.
1348     *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor)
1349     *       closer.eventuallyClose()} for every closeable object this step creates in order to
1350     *       capture it for later closing.
1351     *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
1352     *       ClosingFuture} call {@link #from(ListenableFuture)}.
1353     * </ul>
1354     *
1355     * <p>The same warnings about doing heavyweight operations within {@link
1356     * ClosingFuture#transformAsync(AsyncClosingFunction, Executor)} apply here.
1357     */
1358    public <V extends @Nullable Object> ClosingFuture<V> callAsync(
1359        final AsyncCombiningCallable<V> combiningCallable, Executor executor) {
1360      AsyncCallable<V> asyncCallable =
1361          new AsyncCallable<V>() {
1362            @Override
1363            public ListenableFuture<V> call() throws Exception {
1364              return new Peeker(inputs).callAsync(combiningCallable, closeables);
1365            }
1366
1367            @Override
1368            public String toString() {
1369              return combiningCallable.toString();
1370            }
1371          };
1372      ClosingFuture<V> derived =
1373          new ClosingFuture<>(futureCombiner().callAsync(asyncCallable, executor));
1374      derived.closeables.add(closeables, directExecutor());
1375      return derived;
1376    }
1377
1378    private FutureCombiner<@Nullable Object> futureCombiner() {
1379      return allMustSucceed
1380          ? Futures.whenAllSucceed(inputFutures())
1381          : Futures.whenAllComplete(inputFutures());
1382    }
1383
1384    private static final Function<ClosingFuture<?>, FluentFuture<?>> INNER_FUTURE =
1385        new Function<ClosingFuture<?>, FluentFuture<?>>() {
1386          @Override
1387          public FluentFuture<?> apply(ClosingFuture<?> future) {
1388            return future.future;
1389          }
1390        };
1391
1392    private ImmutableList<FluentFuture<?>> inputFutures() {
1393      return FluentIterable.from(inputs).transform(INNER_FUTURE).toList();
1394    }
1395  }
1396
1397  /**
1398   * A generic {@link Combiner} that lets you use a lambda or method reference to combine two {@link
1399   * ClosingFuture}s. Use {@link #whenAllSucceed(ClosingFuture, ClosingFuture)} to start this
1400   * combination.
1401   *
1402   * @param <V1> the type returned by the first future
1403   * @param <V2> the type returned by the second future
1404   */
1405  public static final class Combiner2<V1 extends @Nullable Object, V2 extends @Nullable Object>
1406      extends Combiner {
1407
1408    /**
1409     * A function that returns a value when applied to the values of the two futures passed to
1410     * {@link #whenAllSucceed(ClosingFuture, ClosingFuture)}.
1411     *
1412     * @param <V1> the type returned by the first future
1413     * @param <V2> the type returned by the second future
1414     * @param <U> the type returned by the function
1415     */
1416    public interface ClosingFunction2<
1417        V1 extends @Nullable Object, V2 extends @Nullable Object, U extends @Nullable Object> {
1418
1419      /**
1420       * Applies this function to two inputs, or throws an exception if unable to do so.
1421       *
1422       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1423       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1424       * is done (but not before this method completes), even if this method throws or the pipeline
1425       * is cancelled.
1426       */
1427      @ParametricNullness
1428      U apply(DeferredCloser closer, @ParametricNullness V1 value1, @ParametricNullness V2 value2)
1429          throws Exception;
1430    }
1431
1432    /**
1433     * A function that returns a {@link ClosingFuture} when applied to the values of the two futures
1434     * passed to {@link #whenAllSucceed(ClosingFuture, ClosingFuture)}.
1435     *
1436     * @param <V1> the type returned by the first future
1437     * @param <V2> the type returned by the second future
1438     * @param <U> the type returned by the function
1439     */
1440    public interface AsyncClosingFunction2<
1441        V1 extends @Nullable Object, V2 extends @Nullable Object, U extends @Nullable Object> {
1442
1443      /**
1444       * Applies this function to two inputs, or throws an exception if unable to do so.
1445       *
1446       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1447       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1448       * is done (but not before this method completes), even if this method throws or the pipeline
1449       * is cancelled.
1450       */
1451      ClosingFuture<U> apply(
1452          DeferredCloser closer, @ParametricNullness V1 value1, @ParametricNullness V2 value2)
1453          throws Exception;
1454    }
1455
1456    private final ClosingFuture<V1> future1;
1457    private final ClosingFuture<V2> future2;
1458
1459    private Combiner2(ClosingFuture<V1> future1, ClosingFuture<V2> future2) {
1460      super(true, ImmutableList.of(future1, future2));
1461      this.future1 = future1;
1462      this.future2 = future2;
1463    }
1464
1465    /**
1466     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1467     * combining function to their values. The function can use a {@link DeferredCloser} to capture
1468     * objects to be closed when the pipeline is done.
1469     *
1470     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture)} and
1471     * any of the inputs fail, so will the returned step.
1472     *
1473     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1474     *
1475     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1476     * ExecutionException} will be extracted and used as the failure of the derived step.
1477     */
1478    public <U extends @Nullable Object> ClosingFuture<U> call(
1479        final ClosingFunction2<V1, V2, U> function, Executor executor) {
1480      return call(
1481          new CombiningCallable<U>() {
1482            @Override
1483            @ParametricNullness
1484            public U call(DeferredCloser closer, Peeker peeker) throws Exception {
1485              return function.apply(closer, peeker.getDone(future1), peeker.getDone(future2));
1486            }
1487
1488            @Override
1489            public String toString() {
1490              return function.toString();
1491            }
1492          },
1493          executor);
1494    }
1495
1496    /**
1497     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1498     * {@code ClosingFuture}-returning function to their values. The function can use a {@link
1499     * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
1500     * captured by the returned {@link ClosingFuture}).
1501     *
1502     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture)} and
1503     * any of the inputs fail, so will the returned step.
1504     *
1505     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1506     *
1507     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1508     * ExecutionException} will be extracted and used as the failure of the derived step.
1509     *
1510     * <p>If the function throws any other exception, it will be used as the failure of the derived
1511     * step.
1512     *
1513     * <p>If an exception is thrown after the function creates a {@code ClosingFuture}, then none of
1514     * the closeable objects in that {@code ClosingFuture} will be closed.
1515     *
1516     * <p>Usage guidelines for this method:
1517     *
1518     * <ul>
1519     *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
1520     *       {@code ClosingFuture}. If possible, prefer calling {@link #call(CombiningCallable,
1521     *       Executor)} instead, with a function that returns the next value directly.
1522     *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor)
1523     *       closer.eventuallyClose()} for every closeable object this step creates in order to
1524     *       capture it for later closing.
1525     *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
1526     *       ClosingFuture} call {@link #from(ListenableFuture)}.
1527     * </ul>
1528     *
1529     * <p>The same warnings about doing heavyweight operations within {@link
1530     * ClosingFuture#transformAsync(AsyncClosingFunction, Executor)} apply here.
1531     */
1532    public <U extends @Nullable Object> ClosingFuture<U> callAsync(
1533        final AsyncClosingFunction2<V1, V2, U> function, Executor executor) {
1534      return callAsync(
1535          new AsyncCombiningCallable<U>() {
1536            @Override
1537            public ClosingFuture<U> call(DeferredCloser closer, Peeker peeker) throws Exception {
1538              return function.apply(closer, peeker.getDone(future1), peeker.getDone(future2));
1539            }
1540
1541            @Override
1542            public String toString() {
1543              return function.toString();
1544            }
1545          },
1546          executor);
1547    }
1548  }
1549
1550  /**
1551   * A generic {@link Combiner} that lets you use a lambda or method reference to combine three
1552   * {@link ClosingFuture}s. Use {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
1553   * ClosingFuture)} to start this combination.
1554   *
1555   * @param <V1> the type returned by the first future
1556   * @param <V2> the type returned by the second future
1557   * @param <V3> the type returned by the third future
1558   */
1559  public static final class Combiner3<
1560          V1 extends @Nullable Object, V2 extends @Nullable Object, V3 extends @Nullable Object>
1561      extends Combiner {
1562    /**
1563     * A function that returns a value when applied to the values of the three futures passed to
1564     * {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture)}.
1565     *
1566     * @param <V1> the type returned by the first future
1567     * @param <V2> the type returned by the second future
1568     * @param <V3> the type returned by the third future
1569     * @param <U> the type returned by the function
1570     */
1571    public interface ClosingFunction3<
1572        V1 extends @Nullable Object,
1573        V2 extends @Nullable Object,
1574        V3 extends @Nullable Object,
1575        U extends @Nullable Object> {
1576      /**
1577       * Applies this function to three inputs, or throws an exception if unable to do so.
1578       *
1579       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1580       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1581       * is done (but not before this method completes), even if this method throws or the pipeline
1582       * is cancelled.
1583       */
1584      @ParametricNullness
1585      U apply(
1586          DeferredCloser closer,
1587          @ParametricNullness V1 value1,
1588          @ParametricNullness V2 value2,
1589          @ParametricNullness V3 value3)
1590          throws Exception;
1591    }
1592
1593    /**
1594     * A function that returns a {@link ClosingFuture} when applied to the values of the three
1595     * futures passed to {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture)}.
1596     *
1597     * @param <V1> the type returned by the first future
1598     * @param <V2> the type returned by the second future
1599     * @param <V3> the type returned by the third future
1600     * @param <U> the type returned by the function
1601     */
1602    public interface AsyncClosingFunction3<
1603        V1 extends @Nullable Object,
1604        V2 extends @Nullable Object,
1605        V3 extends @Nullable Object,
1606        U extends @Nullable Object> {
1607      /**
1608       * Applies this function to three inputs, or throws an exception if unable to do so.
1609       *
1610       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1611       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1612       * is done (but not before this method completes), even if this method throws or the pipeline
1613       * is cancelled.
1614       */
1615      ClosingFuture<U> apply(
1616          DeferredCloser closer,
1617          @ParametricNullness V1 value1,
1618          @ParametricNullness V2 value2,
1619          @ParametricNullness V3 value3)
1620          throws Exception;
1621    }
1622
1623    private final ClosingFuture<V1> future1;
1624    private final ClosingFuture<V2> future2;
1625    private final ClosingFuture<V3> future3;
1626
1627    private Combiner3(
1628        ClosingFuture<V1> future1, ClosingFuture<V2> future2, ClosingFuture<V3> future3) {
1629      super(true, ImmutableList.of(future1, future2, future3));
1630      this.future1 = future1;
1631      this.future2 = future2;
1632      this.future3 = future3;
1633    }
1634
1635    /**
1636     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1637     * combining function to their values. The function can use a {@link DeferredCloser} to capture
1638     * objects to be closed when the pipeline is done.
1639     *
1640     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
1641     * ClosingFuture)} and any of the inputs fail, so will the returned step.
1642     *
1643     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1644     *
1645     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1646     * ExecutionException} will be extracted and used as the failure of the derived step.
1647     */
1648    public <U extends @Nullable Object> ClosingFuture<U> call(
1649        final ClosingFunction3<V1, V2, V3, U> function, Executor executor) {
1650      return call(
1651          new CombiningCallable<U>() {
1652            @Override
1653            @ParametricNullness
1654            public U call(DeferredCloser closer, Peeker peeker) throws Exception {
1655              return function.apply(
1656                  closer,
1657                  peeker.getDone(future1),
1658                  peeker.getDone(future2),
1659                  peeker.getDone(future3));
1660            }
1661
1662            @Override
1663            public String toString() {
1664              return function.toString();
1665            }
1666          },
1667          executor);
1668    }
1669
1670    /**
1671     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1672     * {@code ClosingFuture}-returning function to their values. The function can use a {@link
1673     * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
1674     * captured by the returned {@link ClosingFuture}).
1675     *
1676     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
1677     * ClosingFuture)} and any of the inputs fail, so will the returned step.
1678     *
1679     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1680     *
1681     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1682     * ExecutionException} will be extracted and used as the failure of the derived step.
1683     *
1684     * <p>If the function throws any other exception, it will be used as the failure of the derived
1685     * step.
1686     *
1687     * <p>If an exception is thrown after the function creates a {@code ClosingFuture}, then none of
1688     * the closeable objects in that {@code ClosingFuture} will be closed.
1689     *
1690     * <p>Usage guidelines for this method:
1691     *
1692     * <ul>
1693     *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
1694     *       {@code ClosingFuture}. If possible, prefer calling {@link #call(CombiningCallable,
1695     *       Executor)} instead, with a function that returns the next value directly.
1696     *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor)
1697     *       closer.eventuallyClose()} for every closeable object this step creates in order to
1698     *       capture it for later closing.
1699     *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
1700     *       ClosingFuture} call {@link #from(ListenableFuture)}.
1701     * </ul>
1702     *
1703     * <p>The same warnings about doing heavyweight operations within {@link
1704     * ClosingFuture#transformAsync(AsyncClosingFunction, Executor)} apply here.
1705     */
1706    public <U extends @Nullable Object> ClosingFuture<U> callAsync(
1707        final AsyncClosingFunction3<V1, V2, V3, U> function, Executor executor) {
1708      return callAsync(
1709          new AsyncCombiningCallable<U>() {
1710            @Override
1711            public ClosingFuture<U> call(DeferredCloser closer, Peeker peeker) throws Exception {
1712              return function.apply(
1713                  closer,
1714                  peeker.getDone(future1),
1715                  peeker.getDone(future2),
1716                  peeker.getDone(future3));
1717            }
1718
1719            @Override
1720            public String toString() {
1721              return function.toString();
1722            }
1723          },
1724          executor);
1725    }
1726  }
1727
1728  /**
1729   * A generic {@link Combiner} that lets you use a lambda or method reference to combine four
1730   * {@link ClosingFuture}s. Use {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture,
1731   * ClosingFuture)} to start this combination.
1732   *
1733   * @param <V1> the type returned by the first future
1734   * @param <V2> the type returned by the second future
1735   * @param <V3> the type returned by the third future
1736   * @param <V4> the type returned by the fourth future
1737   */
1738  public static final class Combiner4<
1739          V1 extends @Nullable Object,
1740          V2 extends @Nullable Object,
1741          V3 extends @Nullable Object,
1742          V4 extends @Nullable Object>
1743      extends Combiner {
1744    /**
1745     * A function that returns a value when applied to the values of the four futures passed to
1746     * {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture, ClosingFuture)}.
1747     *
1748     * @param <V1> the type returned by the first future
1749     * @param <V2> the type returned by the second future
1750     * @param <V3> the type returned by the third future
1751     * @param <V4> the type returned by the fourth future
1752     * @param <U> the type returned by the function
1753     */
1754    public interface ClosingFunction4<
1755        V1 extends @Nullable Object,
1756        V2 extends @Nullable Object,
1757        V3 extends @Nullable Object,
1758        V4 extends @Nullable Object,
1759        U extends @Nullable Object> {
1760      /**
1761       * Applies this function to four inputs, or throws an exception if unable to do so.
1762       *
1763       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1764       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1765       * is done (but not before this method completes), even if this method throws or the pipeline
1766       * is cancelled.
1767       */
1768      @ParametricNullness
1769      U apply(
1770          DeferredCloser closer,
1771          @ParametricNullness V1 value1,
1772          @ParametricNullness V2 value2,
1773          @ParametricNullness V3 value3,
1774          @ParametricNullness V4 value4)
1775          throws Exception;
1776    }
1777
1778    /**
1779     * A function that returns a {@link ClosingFuture} when applied to the values of the four
1780     * futures passed to {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture,
1781     * ClosingFuture)}.
1782     *
1783     * @param <V1> the type returned by the first future
1784     * @param <V2> the type returned by the second future
1785     * @param <V3> the type returned by the third future
1786     * @param <V4> the type returned by the fourth future
1787     * @param <U> the type returned by the function
1788     */
1789    public interface AsyncClosingFunction4<
1790        V1 extends @Nullable Object,
1791        V2 extends @Nullable Object,
1792        V3 extends @Nullable Object,
1793        V4 extends @Nullable Object,
1794        U extends @Nullable Object> {
1795      /**
1796       * Applies this function to four inputs, or throws an exception if unable to do so.
1797       *
1798       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1799       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1800       * is done (but not before this method completes), even if this method throws or the pipeline
1801       * is cancelled.
1802       */
1803      ClosingFuture<U> apply(
1804          DeferredCloser closer,
1805          @ParametricNullness V1 value1,
1806          @ParametricNullness V2 value2,
1807          @ParametricNullness V3 value3,
1808          @ParametricNullness V4 value4)
1809          throws Exception;
1810    }
1811
1812    private final ClosingFuture<V1> future1;
1813    private final ClosingFuture<V2> future2;
1814    private final ClosingFuture<V3> future3;
1815    private final ClosingFuture<V4> future4;
1816
1817    private Combiner4(
1818        ClosingFuture<V1> future1,
1819        ClosingFuture<V2> future2,
1820        ClosingFuture<V3> future3,
1821        ClosingFuture<V4> future4) {
1822      super(true, ImmutableList.of(future1, future2, future3, future4));
1823      this.future1 = future1;
1824      this.future2 = future2;
1825      this.future3 = future3;
1826      this.future4 = future4;
1827    }
1828
1829    /**
1830     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1831     * combining function to their values. The function can use a {@link DeferredCloser} to capture
1832     * objects to be closed when the pipeline is done.
1833     *
1834     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
1835     * ClosingFuture, ClosingFuture)} and any of the inputs fail, so will the returned step.
1836     *
1837     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1838     *
1839     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1840     * ExecutionException} will be extracted and used as the failure of the derived step.
1841     */
1842    public <U extends @Nullable Object> ClosingFuture<U> call(
1843        final ClosingFunction4<V1, V2, V3, V4, U> function, Executor executor) {
1844      return call(
1845          new CombiningCallable<U>() {
1846            @Override
1847            @ParametricNullness
1848            public U call(DeferredCloser closer, Peeker peeker) throws Exception {
1849              return function.apply(
1850                  closer,
1851                  peeker.getDone(future1),
1852                  peeker.getDone(future2),
1853                  peeker.getDone(future3),
1854                  peeker.getDone(future4));
1855            }
1856
1857            @Override
1858            public String toString() {
1859              return function.toString();
1860            }
1861          },
1862          executor);
1863    }
1864
1865    /**
1866     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
1867     * {@code ClosingFuture}-returning function to their values. The function can use a {@link
1868     * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
1869     * captured by the returned {@link ClosingFuture}).
1870     *
1871     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
1872     * ClosingFuture, ClosingFuture)} and any of the inputs fail, so will the returned step.
1873     *
1874     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
1875     *
1876     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
1877     * ExecutionException} will be extracted and used as the failure of the derived step.
1878     *
1879     * <p>If the function throws any other exception, it will be used as the failure of the derived
1880     * step.
1881     *
1882     * <p>If an exception is thrown after the function creates a {@code ClosingFuture}, then none of
1883     * the closeable objects in that {@code ClosingFuture} will be closed.
1884     *
1885     * <p>Usage guidelines for this method:
1886     *
1887     * <ul>
1888     *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
1889     *       {@code ClosingFuture}. If possible, prefer calling {@link #call(CombiningCallable,
1890     *       Executor)} instead, with a function that returns the next value directly.
1891     *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor)
1892     *       closer.eventuallyClose()} for every closeable object this step creates in order to
1893     *       capture it for later closing.
1894     *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
1895     *       ClosingFuture} call {@link #from(ListenableFuture)}.
1896     * </ul>
1897     *
1898     * <p>The same warnings about doing heavyweight operations within {@link
1899     * ClosingFuture#transformAsync(AsyncClosingFunction, Executor)} apply here.
1900     */
1901    public <U extends @Nullable Object> ClosingFuture<U> callAsync(
1902        final AsyncClosingFunction4<V1, V2, V3, V4, U> function, Executor executor) {
1903      return callAsync(
1904          new AsyncCombiningCallable<U>() {
1905            @Override
1906            public ClosingFuture<U> call(DeferredCloser closer, Peeker peeker) throws Exception {
1907              return function.apply(
1908                  closer,
1909                  peeker.getDone(future1),
1910                  peeker.getDone(future2),
1911                  peeker.getDone(future3),
1912                  peeker.getDone(future4));
1913            }
1914
1915            @Override
1916            public String toString() {
1917              return function.toString();
1918            }
1919          },
1920          executor);
1921    }
1922  }
1923
1924  /**
1925   * A generic {@link Combiner} that lets you use a lambda or method reference to combine five
1926   * {@link ClosingFuture}s. Use {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture,
1927   * ClosingFuture, ClosingFuture)} to start this combination.
1928   *
1929   * @param <V1> the type returned by the first future
1930   * @param <V2> the type returned by the second future
1931   * @param <V3> the type returned by the third future
1932   * @param <V4> the type returned by the fourth future
1933   * @param <V5> the type returned by the fifth future
1934   */
1935  public static final class Combiner5<
1936          V1 extends @Nullable Object,
1937          V2 extends @Nullable Object,
1938          V3 extends @Nullable Object,
1939          V4 extends @Nullable Object,
1940          V5 extends @Nullable Object>
1941      extends Combiner {
1942    /**
1943     * A function that returns a value when applied to the values of the five futures passed to
1944     * {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture, ClosingFuture,
1945     * ClosingFuture)}.
1946     *
1947     * @param <V1> the type returned by the first future
1948     * @param <V2> the type returned by the second future
1949     * @param <V3> the type returned by the third future
1950     * @param <V4> the type returned by the fourth future
1951     * @param <V5> the type returned by the fifth future
1952     * @param <U> the type returned by the function
1953     */
1954    public interface ClosingFunction5<
1955        V1 extends @Nullable Object,
1956        V2 extends @Nullable Object,
1957        V3 extends @Nullable Object,
1958        V4 extends @Nullable Object,
1959        V5 extends @Nullable Object,
1960        U extends @Nullable Object> {
1961      /**
1962       * Applies this function to five inputs, or throws an exception if unable to do so.
1963       *
1964       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
1965       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
1966       * is done (but not before this method completes), even if this method throws or the pipeline
1967       * is cancelled.
1968       */
1969      @ParametricNullness
1970      U apply(
1971          DeferredCloser closer,
1972          @ParametricNullness V1 value1,
1973          @ParametricNullness V2 value2,
1974          @ParametricNullness V3 value3,
1975          @ParametricNullness V4 value4,
1976          @ParametricNullness V5 value5)
1977          throws Exception;
1978    }
1979
1980    /**
1981     * A function that returns a {@link ClosingFuture} when applied to the values of the five
1982     * futures passed to {@link #whenAllSucceed(ClosingFuture, ClosingFuture, ClosingFuture,
1983     * ClosingFuture, ClosingFuture)}.
1984     *
1985     * @param <V1> the type returned by the first future
1986     * @param <V2> the type returned by the second future
1987     * @param <V3> the type returned by the third future
1988     * @param <V4> the type returned by the fourth future
1989     * @param <V5> the type returned by the fifth future
1990     * @param <U> the type returned by the function
1991     */
1992    public interface AsyncClosingFunction5<
1993        V1 extends @Nullable Object,
1994        V2 extends @Nullable Object,
1995        V3 extends @Nullable Object,
1996        V4 extends @Nullable Object,
1997        V5 extends @Nullable Object,
1998        U extends @Nullable Object> {
1999      /**
2000       * Applies this function to five inputs, or throws an exception if unable to do so.
2001       *
2002       * <p>Any objects that are passed to {@link DeferredCloser#eventuallyClose(Closeable,
2003       * Executor) closer.eventuallyClose()} will be closed when the {@link ClosingFuture} pipeline
2004       * is done (but not before this method completes), even if this method throws or the pipeline
2005       * is cancelled.
2006       */
2007      ClosingFuture<U> apply(
2008          DeferredCloser closer,
2009          @ParametricNullness V1 value1,
2010          @ParametricNullness V2 value2,
2011          @ParametricNullness V3 value3,
2012          @ParametricNullness V4 value4,
2013          @ParametricNullness V5 value5)
2014          throws Exception;
2015    }
2016
2017    private final ClosingFuture<V1> future1;
2018    private final ClosingFuture<V2> future2;
2019    private final ClosingFuture<V3> future3;
2020    private final ClosingFuture<V4> future4;
2021    private final ClosingFuture<V5> future5;
2022
2023    private Combiner5(
2024        ClosingFuture<V1> future1,
2025        ClosingFuture<V2> future2,
2026        ClosingFuture<V3> future3,
2027        ClosingFuture<V4> future4,
2028        ClosingFuture<V5> future5) {
2029      super(true, ImmutableList.of(future1, future2, future3, future4, future5));
2030      this.future1 = future1;
2031      this.future2 = future2;
2032      this.future3 = future3;
2033      this.future4 = future4;
2034      this.future5 = future5;
2035    }
2036
2037    /**
2038     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
2039     * combining function to their values. The function can use a {@link DeferredCloser} to capture
2040     * objects to be closed when the pipeline is done.
2041     *
2042     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
2043     * ClosingFuture, ClosingFuture, ClosingFuture)} and any of the inputs fail, so will the
2044     * returned step.
2045     *
2046     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
2047     *
2048     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
2049     * ExecutionException} will be extracted and used as the failure of the derived step.
2050     */
2051    public <U extends @Nullable Object> ClosingFuture<U> call(
2052        final ClosingFunction5<V1, V2, V3, V4, V5, U> function, Executor executor) {
2053      return call(
2054          new CombiningCallable<U>() {
2055            @Override
2056            @ParametricNullness
2057            public U call(DeferredCloser closer, Peeker peeker) throws Exception {
2058              return function.apply(
2059                  closer,
2060                  peeker.getDone(future1),
2061                  peeker.getDone(future2),
2062                  peeker.getDone(future3),
2063                  peeker.getDone(future4),
2064                  peeker.getDone(future5));
2065            }
2066
2067            @Override
2068            public String toString() {
2069              return function.toString();
2070            }
2071          },
2072          executor);
2073    }
2074
2075    /**
2076     * Returns a new {@code ClosingFuture} pipeline step derived from the inputs by applying a
2077     * {@code ClosingFuture}-returning function to their values. The function can use a {@link
2078     * DeferredCloser} to capture objects to be closed when the pipeline is done (other than those
2079     * captured by the returned {@link ClosingFuture}).
2080     *
2081     * <p>If this combiner was returned by {@link #whenAllSucceed(ClosingFuture, ClosingFuture,
2082     * ClosingFuture, ClosingFuture, ClosingFuture)} and any of the inputs fail, so will the
2083     * returned step.
2084     *
2085     * <p>If the function throws a {@code CancellationException}, the pipeline will be cancelled.
2086     *
2087     * <p>If the function throws an {@code ExecutionException}, the cause of the thrown {@code
2088     * ExecutionException} will be extracted and used as the failure of the derived step.
2089     *
2090     * <p>If the function throws any other exception, it will be used as the failure of the derived
2091     * step.
2092     *
2093     * <p>If an exception is thrown after the function creates a {@code ClosingFuture}, then none of
2094     * the closeable objects in that {@code ClosingFuture} will be closed.
2095     *
2096     * <p>Usage guidelines for this method:
2097     *
2098     * <ul>
2099     *   <li>Use this method only when calling an API that returns a {@link ListenableFuture} or a
2100     *       {@code ClosingFuture}. If possible, prefer calling {@link #call(CombiningCallable,
2101     *       Executor)} instead, with a function that returns the next value directly.
2102     *   <li>Call {@link DeferredCloser#eventuallyClose(Closeable, Executor)
2103     *       closer.eventuallyClose()} for every closeable object this step creates in order to
2104     *       capture it for later closing.
2105     *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
2106     *       ClosingFuture} call {@link #from(ListenableFuture)}.
2107     * </ul>
2108     *
2109     * <p>The same warnings about doing heavyweight operations within {@link
2110     * ClosingFuture#transformAsync(AsyncClosingFunction, Executor)} apply here.
2111     */
2112    public <U extends @Nullable Object> ClosingFuture<U> callAsync(
2113        final AsyncClosingFunction5<V1, V2, V3, V4, V5, U> function, Executor executor) {
2114      return callAsync(
2115          new AsyncCombiningCallable<U>() {
2116            @Override
2117            public ClosingFuture<U> call(DeferredCloser closer, Peeker peeker) throws Exception {
2118              return function.apply(
2119                  closer,
2120                  peeker.getDone(future1),
2121                  peeker.getDone(future2),
2122                  peeker.getDone(future3),
2123                  peeker.getDone(future4),
2124                  peeker.getDone(future5));
2125            }
2126
2127            @Override
2128            public String toString() {
2129              return function.toString();
2130            }
2131          },
2132          executor);
2133    }
2134  }
2135
2136  @Override
2137  public String toString() {
2138    // TODO(dpb): Better toString, in the style of Futures.transform etc.
2139    return toStringHelper(this).add("state", state.get()).addValue(future).toString();
2140  }
2141
2142  @Override
2143  protected void finalize() {
2144    if (state.get().equals(OPEN)) {
2145      logger.log(SEVERE, "Uh oh! An open ClosingFuture has leaked and will close: {0}", this);
2146      FluentFuture<V> unused = finishToFuture();
2147    }
2148  }
2149
2150  private static void closeQuietly(@CheckForNull final Closeable closeable, Executor executor) {
2151    if (closeable == null) {
2152      return;
2153    }
2154    try {
2155      executor.execute(
2156          new Runnable() {
2157            @Override
2158            public void run() {
2159              try {
2160                closeable.close();
2161              } catch (IOException | RuntimeException e) {
2162                logger.log(WARNING, "thrown by close()", e);
2163              }
2164            }
2165          });
2166    } catch (RejectedExecutionException e) {
2167      if (logger.isLoggable(WARNING)) {
2168        logger.log(
2169            WARNING, String.format("while submitting close to %s; will close inline", executor), e);
2170      }
2171      closeQuietly(closeable, directExecutor());
2172    }
2173  }
2174
2175  private void checkAndUpdateState(State oldState, State newState) {
2176    checkState(
2177        compareAndUpdateState(oldState, newState),
2178        "Expected state to be %s, but it was %s",
2179        oldState,
2180        newState);
2181  }
2182
2183  private boolean compareAndUpdateState(State oldState, State newState) {
2184    return state.compareAndSet(oldState, newState);
2185  }
2186
2187  // TODO(dpb): Should we use a pair of ArrayLists instead of an IdentityHashMap?
2188  private static final class CloseableList extends IdentityHashMap<Closeable, Executor>
2189      implements Closeable {
2190    private final DeferredCloser closer = new DeferredCloser(this);
2191    private volatile boolean closed;
2192    @CheckForNull private volatile CountDownLatch whenClosed;
2193
2194    <V extends @Nullable Object, U extends @Nullable Object>
2195        ListenableFuture<U> applyClosingFunction(
2196            ClosingFunction<? super V, U> transformation, @ParametricNullness V input)
2197            throws Exception {
2198      // TODO(dpb): Consider ways to defer closing without creating a separate CloseableList.
2199      CloseableList newCloseables = new CloseableList();
2200      try {
2201        return immediateFuture(transformation.apply(newCloseables.closer, input));
2202      } finally {
2203        add(newCloseables, directExecutor());
2204      }
2205    }
2206
2207    <V extends @Nullable Object, U extends @Nullable Object>
2208        FluentFuture<U> applyAsyncClosingFunction(
2209            AsyncClosingFunction<V, U> transformation, @ParametricNullness V input)
2210            throws Exception {
2211      // TODO(dpb): Consider ways to defer closing without creating a separate CloseableList.
2212      CloseableList newCloseables = new CloseableList();
2213      try {
2214        ClosingFuture<U> closingFuture = transformation.apply(newCloseables.closer, input);
2215        closingFuture.becomeSubsumedInto(newCloseables);
2216        return closingFuture.future;
2217      } finally {
2218        add(newCloseables, directExecutor());
2219      }
2220    }
2221
2222    @Override
2223    public void close() {
2224      if (closed) {
2225        return;
2226      }
2227      synchronized (this) {
2228        if (closed) {
2229          return;
2230        }
2231        closed = true;
2232      }
2233      for (Map.Entry<Closeable, Executor> entry : entrySet()) {
2234        closeQuietly(entry.getKey(), entry.getValue());
2235      }
2236      clear();
2237      if (whenClosed != null) {
2238        whenClosed.countDown();
2239      }
2240    }
2241
2242    void add(@CheckForNull Closeable closeable, Executor executor) {
2243      checkNotNull(executor);
2244      if (closeable == null) {
2245        return;
2246      }
2247      synchronized (this) {
2248        if (!closed) {
2249          put(closeable, executor);
2250          return;
2251        }
2252      }
2253      closeQuietly(closeable, executor);
2254    }
2255
2256    /**
2257     * Returns a latch that reaches zero when this objects' deferred closeables have been closed.
2258     */
2259    CountDownLatch whenClosedCountDown() {
2260      if (closed) {
2261        return new CountDownLatch(0);
2262      }
2263      synchronized (this) {
2264        if (closed) {
2265          return new CountDownLatch(0);
2266        }
2267        checkState(whenClosed == null);
2268        return whenClosed = new CountDownLatch(1);
2269      }
2270    }
2271  }
2272
2273  /**
2274   * Returns an object that can be used to wait until this objects' deferred closeables have all had
2275   * {@link Runnable}s that close them submitted to each one's closing {@link Executor}.
2276   */
2277  @VisibleForTesting
2278  CountDownLatch whenClosedCountDown() {
2279    return closeables.whenClosedCountDown();
2280  }
2281
2282  /** The state of a {@link CloseableList}. */
2283  enum State {
2284    /** The {@link CloseableList} has not been subsumed or closed. */
2285    OPEN,
2286
2287    /**
2288     * The {@link CloseableList} has been subsumed into another. It may not be closed or subsumed
2289     * into any other.
2290     */
2291    SUBSUMED,
2292
2293    /**
2294     * Some {@link ListenableFuture} has a callback attached that will close the {@link
2295     * CloseableList}, but it has not yet run. The {@link CloseableList} may not be subsumed.
2296     */
2297    WILL_CLOSE,
2298
2299    /**
2300     * The callback that closes the {@link CloseableList} is running, but it has not completed. The
2301     * {@link CloseableList} may not be subsumed.
2302     */
2303    CLOSING,
2304
2305    /** The {@link CloseableList} has been closed. It may not be further subsumed. */
2306    CLOSED,
2307
2308    /**
2309     * {@link ClosingFuture#finishToValueAndCloser(ValueAndCloserConsumer, Executor)} has been
2310     * called. The step may not be further subsumed, nor may {@link #finishToFuture()} be called.
2311     */
2312    WILL_CREATE_VALUE_AND_CLOSER,
2313  }
2314}