Package com.google.common.util.concurrent

Class AbstractFuture<V>

    • Field Detail

      • GENERATE_CANCELLATION_CAUSES

        private static final boolean GENERATE_CANCELLATION_CAUSES

      • log

        private static final java.util.logging.Logger log

      • NULL

        private static final java.lang.Object NULL
        A special value to represent null.

      • value

        private volatile java.lang.Object value
        This field encodes the current state of the future.

        The valid values are:

    • Constructor Detail

      • AbstractFuture

        protected AbstractFuture()
        Constructor for use by subclasses.

    • Method Detail

      • removeWaiter

        private void removeWaiter​(AbstractFuture.Waiter node)
        Marks the given node as 'deleted' (null waiter) and then scans the list to unlink all deleted nodes. This is an O(n) operation in the common case (and O(n^2) in the worst), but we are saved by two things.
        • This is only called when a waiting thread times out or is interrupted. Both of which should be rare.
        • The waiters list should be very short.

      • get

        public V get​(long timeout,
             java.util.concurrent.TimeUnit unit)
      throws java.lang.InterruptedException,
             java.util.concurrent.TimeoutException,
             java.util.concurrent.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 java.util.concurrent.Future<V>
        Throws:
        java.util.concurrent.CancellationException
        java.lang.InterruptedException
        java.util.concurrent.TimeoutException
        java.util.concurrent.ExecutionException

      • get

        public V get()
      throws java.lang.InterruptedException,
             java.util.concurrent.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 java.util.concurrent.Future<V>
        Throws:
        java.util.concurrent.CancellationException
        java.lang.InterruptedException
        java.util.concurrent.ExecutionException

      • getDoneValue

        private V getDoneValue​(java.lang.Object obj)
                throws java.util.concurrent.ExecutionException
        Unboxes obj. Assumes that obj is not null or a AbstractFuture.SetFuture.
        Throws:
        java.util.concurrent.ExecutionException

      • isDone

        public boolean isDone()
        Specified by:
        isDone in interface java.util.concurrent.Future<V>

      • isCancelled

        public boolean isCancelled()
        Specified by:
        isCancelled in interface java.util.concurrent.Future<V>

      • cancel

        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).

        Specified by:
        cancel in interface java.util.concurrent.Future<V>

      • 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​(java.lang.Runnable listener,
                        java.util.concurrent.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: For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.directExecutor(). Otherwise, avoid it. Heavyweight directExecutor listeners can cause problems, and these problems can be difficult to reproduce because they depend on timing. For example:

        • The listener may be executed by the caller of addListener. That caller may be a UI thread or other latency-sensitive thread. This can harm UI responsiveness.
        • The listener may be executed by the thread that completes this Future. That thread may be an internal system thread such as an RPC network thread. Blocking that thread may stall progress of the whole system. It may even cause a deadlock.
        • The listener may delay other listeners, even listeners that are not themselves directExecutor listeners.

        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

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

      • setException

        protected boolean setException​(java.lang.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).
        Parameters:
        throwable - the exception to be used as the failed result
        Returns:
        true if the attempt was accepted, completing the Future

      • setFuture

        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.

        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

      • getFutureValue

        private static java.lang.Object getFutureValue​(ListenableFuture<?> future)
        Returns a value that satisfies the contract of the value field based on the state of given future.

        This is approximately the inverse of getDoneValue(Object)

      • getUninterruptibly

        private static <V> V getUninterruptibly​(java.util.concurrent.Future<V> future)
                                 throws java.util.concurrent.ExecutionException
        An inlined private copy of Uninterruptibles.getUninterruptibly(java.util.concurrent.Future<V>) used to break an internal dependency on other /util/concurrent classes.
        Throws:
        java.util.concurrent.ExecutionException

      • complete

        private static void complete​(AbstractFuture<?> future)
        Unblocks all threads and runs all listeners.

      • afterDone

        @Beta
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 java.lang.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 InternalFutureFailureAccess
        Since:
        27.0

      • maybePropagateCancellationTo

        final void maybePropagateCancellationTo​(java.util.concurrent.Future<?> related)
        If this future has been cancelled (and possibly interrupted), cancels (and possibly interrupts) the given future (if available).

      • releaseWaiters

        private void releaseWaiters()
        Releases all threads in the waiters list, and clears the list.

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object

      • pendingToString

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

      • addDoneString

        private void addDoneString​(java.lang.StringBuilder builder)

      • userObjectToString

        private java.lang.String userObjectToString​(java.lang.Object o)
        Helper for printing user supplied objects into our toString method.

      • executeListener

        private static void executeListener​(java.lang.Runnable runnable,
                                    java.util.concurrent.Executor executor)
        Submits the given runnable to the given Executor catching and logging all runtime exceptions thrown by the executor.

      • cancellationExceptionWithCause

        private static java.util.concurrent.CancellationException cancellationExceptionWithCause​(java.lang.String message,
                                                                                         java.lang.Throwable cause)