- java.lang.Object
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- com.google.common.util.concurrent.internal.InternalFutureFailureAccess
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- com.google.common.util.concurrent.AbstractFuture<V>
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- All Implemented Interfaces:
ListenableFuture<V>
,Future<V>
- Direct Known Subclasses:
FluentFuture
,SettableFuture
@GwtCompatible(emulated=true) public abstract class AbstractFuture<V extends @Nullable Object> extends com.google.common.util.concurrent.internal.InternalFutureFailureAccess implements ListenableFuture<V>
An abstract implementation ofListenableFuture
, intended for advanced users only. More common ways to create aListenableFuture
include instantiating aSettableFuture
, submitting a task to aListeningExecutorService
, and deriving aFuture
from an existing one, typically using methods likeFutures.transform
andFutures.catching
.This class implements all methods in
ListenableFuture
. Subclasses should provide a way to set the result of the computation through the protected methodsset(Object)
,setFuture(ListenableFuture)
andsetException(Throwable)
. Subclasses may also overrideafterDone()
, which will be invoked automatically when the future completes. Subclasses should rarely override other methods.- Since:
- 1.0
- Author:
- Sven Mawson, Luke Sandberg
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Constructor Summary
Constructors Modifier Constructor Description protected
AbstractFuture()
Constructor for use by subclasses.
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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()
Returnstrue
if this task was cancelled before it completed normally.boolean
isDone()
Returnstrue
if this task completed.protected String
pendingToString()
Provide a human-readable explanation of why this future has not yet completed.protected boolean
set(V value)
Sets the result of thisFuture
unless thisFuture
has already been cancelled or set (including set asynchronously).protected boolean
setException(Throwable throwable)
Sets the failed result of thisFuture
unless thisFuture
has already been cancelled or set (including set asynchronously).protected boolean
setFuture(ListenableFuture<? extends V> future)
Sets the result of thisFuture
to match the supplied inputFuture
once the suppliedFuture
is done, unless thisFuture
has already been cancelled or set (including "set asynchronously," defined below).String
toString()
Returns a string representation of the object.protected Throwable
tryInternalFastPathGetFailure()
Usually returnsnull
but, if thisFuture
has failed, may optionally return the cause of the failure.protected boolean
wasInterrupted()
Returns true if this future was cancelled withmayInterruptIfRunning
set totrue
.
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Constructor Detail
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AbstractFuture
protected AbstractFuture()
Constructor for use by subclasses.
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Method Detail
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get
@CanIgnoreReturnValue public V get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException, ExecutionException
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.The default
AbstractFuture
implementation throwsInterruptedException
if the current thread is interrupted during the call, even if the value is already available.- Specified by:
get
in interfaceFuture<V extends @Nullable Object>
- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Returns:
- the computed result
- Throws:
CancellationException
- if the computation was cancelledInterruptedException
- if the current thread was interrupted while waitingTimeoutException
- if the wait timed outExecutionException
- if the computation threw an exception
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get
@CanIgnoreReturnValue public V get() throws InterruptedException, ExecutionException
Waits if necessary for the computation to complete, and then retrieves its result.The default
AbstractFuture
implementation throwsInterruptedException
if the current thread is interrupted during the call, even if the value is already available.- Specified by:
get
in interfaceFuture<V extends @Nullable Object>
- Returns:
- the computed result
- Throws:
CancellationException
- if the computation was cancelledInterruptedException
- if the current thread was interrupted while waitingExecutionException
- if the computation threw an exception
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isDone
public boolean isDone()
Description copied from interface:java.util.concurrent.Future
Returnstrue
if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will returntrue
.
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isCancelled
public boolean isCancelled()
Description copied from interface:java.util.concurrent.Future
Returnstrue
if this task was cancelled before it completed normally.- Specified by:
isCancelled
in interfaceFuture<V extends @Nullable Object>
- Returns:
true
if this task was cancelled before it completed
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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 whencancel
is called, this task should never run. If the task has already started, then themayInterruptIfRunning
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 returntrue
. Subsequent calls toFuture.isCancelled()
will always returntrue
if this method returnedtrue
.If a cancellation attempt succeeds on a
Future
that had previously been set asynchronously, then the cancellation will also be propagated to the delegateFuture
that was supplied in thesetFuture
call.Rather than override this method to perform additional cancellation work or cleanup, subclasses should override
afterDone()
, consultingisCancelled()
andwasInterrupted()
as necessary. This ensures that the work is done even if the future is cancelled without a call tocancel
, such as by callingsetFuture(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 interfaceFuture<V extends @Nullable Object>
- 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
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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 tocancel(true)
.The default implementation does nothing.
This method is likely to be deprecated. Prefer to override
afterDone()
, consultingwasInterrupted()
to decide whether to interrupt your task.- Since:
- 10.0
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wasInterrupted
protected final boolean wasInterrupted()
Returns true if this future was cancelled withmayInterruptIfRunning
set totrue
.- Since:
- 14.0
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addListener
public void addListener(Runnable listener, Executor executor)
Registers a listener to be run on the given executor. The listener will run when theFuture
'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., aRejectedExecutionException
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 -- considerMoreExecutors.directExecutor()
. Otherwise, avoid it: See the warnings on the docs fordirectExecutor
.This is the most general listener interface. For common operations performed using listeners, see
Futures
. For a simplified but general listener interface, seeaddCallback()
.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 interfaceListenableFuture<V extends @Nullable Object>
- Parameters:
listener
- the listener to run when the computation is completeexecutor
- the executor to run the listener in- Since:
- 10.0
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set
@CanIgnoreReturnValue protected boolean set(V value)
Sets the result of thisFuture
unless thisFuture
has already been cancelled or set (including set asynchronously). When a call to this method returns, theFuture
is guaranteed to be done only if the call was accepted (in which case it returnstrue
). If it returnsfalse
, theFuture
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 aset*
method, only by a call tocancel(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
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setException
@CanIgnoreReturnValue protected boolean setException(Throwable throwable)
Sets the failed result of thisFuture
unless thisFuture
has already been cancelled or set (including set asynchronously). When a call to this method returns, theFuture
is guaranteed to be done only if the call was accepted (in which case it returnstrue
). If it returnsfalse
, theFuture
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 aset*
method, only by a call tocancel(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
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setFuture
@CanIgnoreReturnValue protected boolean setFuture(ListenableFuture<? extends V> future)
Sets the result of thisFuture
to match the supplied inputFuture
once the suppliedFuture
is done, unless thisFuture
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 tocancel(boolean)
.If the call
setFuture(delegate)
is accepted and thisFuture
is later cancelled, cancellation will be propagated todelegate
. Additionally, any call tosetFuture
after any cancellation will propagate cancellation to the suppliedFuture
.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 thewasInterrupted()
method will not returntrue
.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
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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
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tryInternalFastPathGetFailure
@CheckForNull protected final Throwable tryInternalFastPathGetFailure()
Usually returnsnull
but, if thisFuture
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 returntrue
isCancelled()
must returnfalse
get()
must not block, and it must throw anExecutionException
with the return value of this method as its cause
This method is
protected
so that classes likecom.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, callInternalFutures.tryInternalFastPathGetFailure(InternalFutureFailureAccess)
.- Specified by:
tryInternalFastPathGetFailure
in classcom.google.common.util.concurrent.internal.InternalFutureFailureAccess
- Since:
- 27.0
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toString
public String toString()
Description copied from class:java.lang.Object
Returns a string representation of the object. In general, thetoString
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 classObject
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())
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pendingToString
@CheckForNull protected 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
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