Package com.google.common.util.concurrent

Class AbstractFuture<V>

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      protected AbstractFuture()
      Constructor for use by subclasses.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void addListener​(Runnable listener, Executor executor)
      Registers a listener to be run on the given executor.
      protected void afterDone()
      Callback method that is called exactly once after the future is completed.
      boolean cancel​(boolean mayInterruptIfRunning)
      Attempts to cancel execution of this task.
      V get()
      Waits if necessary for the computation to complete, and then retrieves its result.
      V get​(long timeout, TimeUnit unit)
      Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
      protected void interruptTask()
      Subclasses can override this method to implement interruption of the future's computation.
      boolean isCancelled()
      Returns true if this task was cancelled before it completed normally.
      boolean isDone()
      Returns true if this task completed.
      protected @Nullable String pendingToString()
      Provide a human-readable explanation of why this future has not yet completed.
      protected boolean set​(@Nullable V value)
      Sets the result of this Future unless this Future has already been cancelled or set (including set asynchronously).
      protected boolean setException​(Throwable throwable)
      Sets the failed result of this Future unless this Future has already been cancelled or set (including set asynchronously).
      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).
      String toString()
      Returns a string representation of the object.
      protected @Nullable Throwable tryInternalFastPathGetFailure()
      Usually returns null but, if this Future has failed, may optionally return the cause of the failure.
      protected boolean wasInterrupted()
      Returns true if this future was cancelled with mayInterruptIfRunning set to true.

    • Constructor Detail

      • AbstractFuture

        protected AbstractFuture()
        Constructor for use by subclasses.

    • Method Detail

      • isDone

        public boolean isDone()
        Description copied from interface: java.util.concurrent.Future
        Returns true if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will return true.
        Specified by:
        isDone in interface Future<V>
        Returns:
        true if this task completed

      • isCancelled

        public boolean isCancelled()
        Description copied from interface: java.util.concurrent.Future
        Returns true if this task was cancelled before it completed normally.
        Specified by:
        isCancelled in interface Future<V>
        Returns:
        true if this task was cancelled before it completed

      • cancel

        @CanIgnoreReturnValue
public boolean cancel​(boolean mayInterruptIfRunning)
        Attempts to cancel execution of this task. This attempt will fail if the task has already completed, has already been cancelled, or could not be cancelled for some other reason. If successful, and this task has not started when cancel is called, this task should never run. If the task has already started, then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.

        After this method returns, subsequent calls to Future.isDone() will always return true. Subsequent calls to Future.isCancelled() will always return true if this method returned true.

        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>
        Parameters:
        mayInterruptIfRunning - true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete
        Returns:
        false if the task could not be cancelled, typically because it has already completed normally; true otherwise

      • 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>
        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​(@Nullable 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

        @Beta
@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()
        Description copied from class: java.lang.Object
        Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

        The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: 

         getClass().getName() + '@' + Integer.toHexString(hashCode())
        Overrides:
        toString in class Object
        Returns:
        a string representation of the 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