com.google.common.util.concurrent

Class AbstractFuture.Sync<V>

java.lang.Object

java.util.concurrent.locks.AbstractOwnableSynchronizer

java.util.concurrent.locks.AbstractQueuedSynchronizer

com.google.common.util.concurrent.AbstractFuture.Sync<V>

All Implemented Interfaces:

java.io.Serializable

Enclosing class:

AbstractFuture<V>

static final class AbstractFuture.Sync<V>
extends java.util.concurrent.locks.AbstractQueuedSynchronizer

Following the contract of AbstractQueuedSynchronizer we create a private subclass to hold the synchronizer. This synchronizer is used to implement the blocking and waiting calls as well as to handle state changes in a thread-safe manner. The current state of the future is held in the Sync state, and the lock is released whenever the state changes to COMPLETED, CANCELLED, or INTERRUPTED

To avoid races between threads doing release and acquire, we transition to the final state in two steps. One thread will successfully CAS from RUNNING to COMPLETING, that thread will then set the result of the computation, and only then transition to COMPLETED, CANCELLED, or INTERRUPTED.

We don't use the integer argument passed between acquire methods so we pass around a -1 everywhere.

Nested Class Summary

Nested classes/interfaces inherited from class java.util.concurrent.locks.AbstractQueuedSynchronizer

java.util.concurrent.locks.AbstractQueuedSynchronizer.ConditionObject

Field Summary

Fields

Modifier and Type	Field and Description
(package private) static int	CANCELLED
(package private) static int	COMPLETED
(package private) static int	COMPLETING
private java.lang.Throwable	exception
(package private) static int	INTERRUPTED
(package private) static int	RUNNING
private static long	serialVersionUID
private V	value

Constructor Summary

Constructors

Constructor and Description
Sync()

Method Summary

Modifier and Type	Method and Description
(package private) boolean	cancel(boolean interrupt) Transition to the CANCELLED or INTERRUPTED state.
private boolean	complete(V v, java.lang.Throwable t, int finalState) Implementation of completing a task.
(package private) V	get() Blocks until complete(Object, Throwable, int) has been successfully called.
(package private) V	get(long nanos) Blocks until the task is complete or the timeout expires.
private V	getValue() Implementation of the actual value retrieval.
(package private) boolean	isCancelled() Checks if the state is CANCELLED or INTERRUPTED.
(package private) boolean	isDone() Checks if the state is COMPLETED, CANCELLED, or INTERRUPTED.
(package private) boolean	set(V v) Transition to the COMPLETED state and set the value.
(package private) boolean	setException(java.lang.Throwable t) Transition to the COMPLETED state and set the exception.
protected int	tryAcquireShared(int ignored)
protected boolean	tryReleaseShared(int finalState)
(package private) boolean	wasInterrupted() Checks if the state is INTERRUPTED.

Methods inherited from class java.util.concurrent.locks.AbstractQueuedSynchronizer

acquire, acquireInterruptibly, acquireShared, acquireSharedInterruptibly, compareAndSetState, getExclusiveQueuedThreads, getFirstQueuedThread, getQueuedThreads, getQueueLength, getSharedQueuedThreads, getState, getWaitingThreads, getWaitQueueLength, hasContended, hasQueuedPredecessors, hasQueuedThreads, hasWaiters, isHeldExclusively, isQueued, owns, release, releaseShared, setState, toString, tryAcquire, tryAcquireNanos, tryAcquireSharedNanos, tryRelease

Methods inherited from class java.util.concurrent.locks.AbstractOwnableSynchronizer

getExclusiveOwnerThread, setExclusiveOwnerThread

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

RUNNING

static final int RUNNING

See Also:

Constant Field Values

COMPLETING

static final int COMPLETING

See Also:

Constant Field Values

COMPLETED

static final int COMPLETED

See Also:

Constant Field Values

CANCELLED

static final int CANCELLED

See Also:

Constant Field Values

INTERRUPTED

static final int INTERRUPTED

See Also:

Constant Field Values

value

private V value

exception

private java.lang.Throwable exception

Constructor Detail

Sync

Sync()

Method Detail

tryAcquireShared

protected int tryAcquireShared(int ignored)

Overrides:

tryAcquireShared in class java.util.concurrent.locks.AbstractQueuedSynchronizer

tryReleaseShared

protected boolean tryReleaseShared(int finalState)

Overrides:

tryReleaseShared in class java.util.concurrent.locks.AbstractQueuedSynchronizer

get

V get(long nanos)
throws java.util.concurrent.TimeoutException,
      java.util.concurrent.CancellationException,
      java.util.concurrent.ExecutionException,
      java.lang.InterruptedException

Blocks until the task is complete or the timeout expires. Throws a TimeoutException if the timer expires, otherwise behaves like get().

Throws:

java.util.concurrent.TimeoutException

java.util.concurrent.CancellationException

java.util.concurrent.ExecutionException

java.lang.InterruptedException

get

V get()
throws java.util.concurrent.CancellationException,
      java.util.concurrent.ExecutionException,
      java.lang.InterruptedException

Blocks until complete(Object, Throwable, int) has been successfully called. Throws a CancellationException if the task was cancelled, or a ExecutionException if the task completed with an error.

Throws:

java.util.concurrent.CancellationException

java.util.concurrent.ExecutionException

java.lang.InterruptedException

getValue

private V getValue()
            throws java.util.concurrent.CancellationException,
                   java.util.concurrent.ExecutionException

Implementation of the actual value retrieval. Will return the value on success, an exception on failure, a cancellation on cancellation, or an illegal state if the synchronizer is in an invalid state.

Throws:

java.util.concurrent.CancellationException

java.util.concurrent.ExecutionException

isDone

boolean isDone()

Checks if the state is COMPLETED, CANCELLED, or INTERRUPTED.

isCancelled

boolean isCancelled()

Checks if the state is CANCELLED or INTERRUPTED.

wasInterrupted

boolean wasInterrupted()

Checks if the state is INTERRUPTED.

set

boolean set(@Nullable
            V v)

Transition to the COMPLETED state and set the value.

setException

boolean setException(java.lang.Throwable t)

Transition to the COMPLETED state and set the exception.

cancel

boolean cancel(boolean interrupt)

Transition to the CANCELLED or INTERRUPTED state.

complete

private boolean complete(@Nullable
                         V v,
                         @Nullable
                         java.lang.Throwable t,
                         int finalState)

Implementation of completing a task. Either v or t will be set but not both. The finalState is the state to change to from RUNNING. If the state is not in the RUNNING state we return false after waiting for the state to be set to a valid final state (COMPLETED, CANCELLED, or INTERRUPTED).

Parameters:

v - the value to set as the result of the computation.

t - the exception to set as the result of the computation.

finalState - the state to transition to.