Class AbstractFuture<V extends @Nullable Object>

java.lang.Object
com.google.common.util.concurrent.internal.InternalFutureFailureAccess
com.google.common.util.concurrent.AbstractFuture<V>
All Implemented Interfaces:
ListenableFuture<V>, Future<V>
Direct Known Subclasses:
FluentFuture, SettableFuture
@GwtCompatible(emulated=true) @ReflectionSupport(FULL) public abstract class AbstractFuture<V extends @Nullable Object> extends com.google.common.util.concurrent.internal.InternalFutureFailureAccess implements ListenableFuture<V>
An abstract implementation of ListenableFuture, intended for advanced users only. More common ways to create a ListenableFuture include instantiating a SettableFuture, submitting a task to a ListeningExecutorService, and deriving a Future from an existing one, typically using methods like Futures.transform and Futures.catching.

This class implements all methods in ListenableFuture. Subclasses should provide a way to set the result of the computation through the protected methods set(Object), setFuture(ListenableFuture) and setException(Throwable). Subclasses may also override afterDone(), which will be invoked automatically when the future completes. Subclasses should rarely override other methods.

Since:
1.0
Author:
Sven Mawson, Luke Sandberg

  • Constructor Details

    • AbstractFuture

      protected AbstractFuture()
      Constructor for use by subclasses.

  • Method Details

    • get

      @CanIgnoreReturnValue public V get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException, ExecutionException

      The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted during the call, even if the value is already available.

      Specified by:
      get in interface Future<V extends @Nullable Object>

    • get

      @CanIgnoreReturnValue public V get() throws InterruptedException, ExecutionException

      The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted during the call, even if the value is already available.

      Specified by:
      get in interface Future<V extends @Nullable Object>

    • isDone

      public boolean isDone()
      Specified by:
      isDone in interface Future<V extends @Nullable Object>

    • isCancelled

      public boolean isCancelled()
      Specified by:
      isCancelled in interface Future<V extends @Nullable Object>

    • cancel

      @CanIgnoreReturnValue public boolean cancel(boolean mayInterruptIfRunning)

      If a cancellation attempt succeeds on a Future that had previously been set asynchronously, then the cancellation will also be propagated to the delegate Future that was supplied in the setFuture call.

      Rather than override this method to perform additional cancellation work or cleanup, subclasses should override afterDone(), consulting isCancelled() and wasInterrupted() as necessary. This ensures that the work is done even if the future is cancelled without a call to cancel, such as by calling setFuture(cancelledFuture).

      Beware of completing a future while holding a lock. Its listeners may do slow work or acquire other locks, risking deadlocks.

      Specified by:
      cancel in interface Future<V extends @Nullable Object>

    • interruptTask

      protected void interruptTask()
      Subclasses can override this method to implement interruption of the future's computation. The method is invoked automatically by a successful call to cancel(true).

      The default implementation does nothing.

      This method is likely to be deprecated. Prefer to override afterDone(), checking wasInterrupted() to decide whether to interrupt your task.

      Since:
      10.0

    • wasInterrupted

      protected final boolean wasInterrupted()
      Returns true if this future was cancelled with mayInterruptIfRunning set to true.
      Since:
      14.0

    • addListener

      public void addListener(Runnable listener, Executor executor)
      Registers a listener to be run on the given executor. The listener will run when the Future's computation is complete or, if the computation is already complete, immediately.

      There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called once the computation is complete.

      Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException or an exception thrown by direct execution) will be caught and logged.

      Note: If your listener is lightweight -- and will not cause stack overflow by completing more futures or adding more directExecutor() listeners inline -- consider MoreExecutors.directExecutor(). Otherwise, avoid it: See the warnings on the docs for directExecutor.

      This is the most general listener interface. For common operations performed using listeners, see Futures. For a simplified but general listener interface, see addCallback().

      Memory consistency effects: Actions in a thread prior to adding a listener happen-before its execution begins, perhaps in another thread.

      Guava implementations of ListenableFuture promptly release references to listeners after executing them.

      Specified by:
      addListener in interface ListenableFuture<V extends @Nullable Object>
      Parameters:
      listener - the listener to run when the computation is complete
      executor - the executor to run the listener in
      Since:
      10.0

    • set

      @CanIgnoreReturnValue protected boolean set(V value)
      Sets the result of this Future unless this Future has already been cancelled or set (including set asynchronously). When a call to this method returns, the Future is guaranteed to be done only if the call was accepted (in which case it returns true). If it returns false, the Future may have previously been set asynchronously, in which case its result may not be known yet. That result, though not yet known, cannot be overridden by a call to a set* method, only by a call to cancel(boolean).

      Beware of completing a future while holding a lock. Its listeners may do slow work or acquire other locks, risking deadlocks.

      Parameters:
      value - the value to be used as the result
      Returns:
      true if the attempt was accepted, completing the Future

    • setException

      @CanIgnoreReturnValue protected boolean setException(Throwable throwable)
      Sets the failed result of this Future unless this Future has already been cancelled or set (including set asynchronously). When a call to this method returns, the Future is guaranteed to be done only if the call was accepted (in which case it returns true). If it returns false, the Future may have previously been set asynchronously, in which case its result may not be known yet. That result, though not yet known, cannot be overridden by a call to a set* method, only by a call to cancel(boolean).

      Beware of completing a future while holding a lock. Its listeners may do slow work or acquire other locks, risking deadlocks.

      Parameters:
      throwable - the exception to be used as the failed result
      Returns:
      true if the attempt was accepted, completing the Future

    • setFuture

      @CanIgnoreReturnValue protected boolean setFuture(ListenableFuture<? extends V> future)
      Sets the result of this Future to match the supplied input Future once the supplied Future is done, unless this Future has already been cancelled or set (including "set asynchronously," defined below).

      If the supplied future is done when this method is called and the call is accepted, then this future is guaranteed to have been completed with the supplied future by the time this method returns. If the supplied future is not done and the call is accepted, then the future will be set asynchronously. Note that such a result, though not yet known, cannot be overridden by a call to a set* method, only by a call to cancel(boolean).

      If the call setFuture(delegate) is accepted and this Future is later cancelled, cancellation will be propagated to delegate. Additionally, any call to setFuture after any cancellation will propagate cancellation to the supplied Future.

      Note that, even if the supplied future is cancelled and it causes this future to complete, it will never trigger interruption behavior. In particular, it will not cause this future to invoke the interruptTask() method, and the wasInterrupted() method will not return true.

      Beware of completing a future while holding a lock. Its listeners may do slow work or acquire other locks, risking deadlocks.

      Parameters:
      future - the future to delegate to
      Returns:
      true if the attempt was accepted, indicating that the Future was not previously cancelled or set.
      Since:
      19.0

    • afterDone

      @ForOverride protected void afterDone()
      Callback method that is called exactly once after the future is completed.

      If interruptTask() is also run during completion, afterDone() runs after it.

      The default implementation of this method in AbstractFuture does nothing. This is intended for very lightweight cleanup work, for example, timing statistics or clearing fields. If your task does anything heavier consider, just using a listener with an executor.

      Since:
      20.0

    • tryInternalFastPathGetFailure

      protected final @Nullable Throwable tryInternalFastPathGetFailure()
      Usually returns null but, if this Future has failed, may optionally return the cause of the failure. "Failure" means specifically "completed with an exception"; it does not include "was cancelled." To be explicit: If this method returns a non-null value, then:
      • isDone() must return true
      • isCancelled() must return false
      • get() must not block, and it must throw an ExecutionException with the return value of this method as its cause

      This method is protected so that classes like com.google.common.util.concurrent.SettableFuture do not expose it to their users as an instance method. In the unlikely event that you need to call this method, call InternalFutures.tryInternalFastPathGetFailure(InternalFutureFailureAccess).

      Specified by:
      tryInternalFastPathGetFailure in class com.google.common.util.concurrent.internal.InternalFutureFailureAccess
      Since:
      27.0

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • pendingToString

      protected @Nullable String pendingToString()
      Provide a human-readable explanation of why this future has not yet completed.
      Returns:
      null if an explanation cannot be provided (e.g. because the future is done).
      Since:
      23.0