Class AbstractFuture<V>
- java.lang.Object
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- com.google.common.util.concurrent.AbstractFuture<V>
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- All Implemented Interfaces:
ListenableFuture<V>
,java.util.concurrent.Future<V>
- Direct Known Subclasses:
SettableFuture
@GwtCompatible(emulated=true) public abstract class AbstractFuture<V> extends java.lang.Object 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 overrideinterruptTask()
, which will be invoked automatically if a call tocancel(true)
succeeds in canceling the future. Subclasses should rarely override other methods.- Since:
- 1.0
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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(java.lang.Runnable listener, java.util.concurrent.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)
V
get()
V
get(long timeout, java.util.concurrent.TimeUnit unit)
protected void
interruptTask()
Subclasses can override this method to implement interruption of the future's computation.boolean
isCancelled()
boolean
isDone()
protected boolean
set(V value)
Sets the result of thisFuture
unless thisFuture
has already been cancelled or set (including set asynchronously).protected boolean
setException(java.lang.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).protected boolean
wasInterrupted()
Returns true if this future was cancelled withmayInterruptIfRunning
set totrue
.
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Method Detail
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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 throwsInterruptedException
if the current thread is interrupted before or during the call, even if the value is already available.- Specified by:
get
in interfacejava.util.concurrent.Future<V>
- Throws:
java.lang.InterruptedException
- if the current thread was interrupted before or during the call (optional but recommended).java.util.concurrent.CancellationException
java.util.concurrent.TimeoutException
java.util.concurrent.ExecutionException
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get
public V get() throws java.lang.InterruptedException, java.util.concurrent.ExecutionException
The default
AbstractFuture
implementation throwsInterruptedException
if the current thread is interrupted before or during the call, even if the value is already available.- Specified by:
get
in interfacejava.util.concurrent.Future<V>
- Throws:
java.lang.InterruptedException
- if the current thread was interrupted before or during the call (optional but recommended).java.util.concurrent.CancellationException
java.util.concurrent.ExecutionException
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isDone
public boolean isDone()
- Specified by:
isDone
in interfacejava.util.concurrent.Future<V>
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isCancelled
public boolean isCancelled()
- Specified by:
isCancelled
in interfacejava.util.concurrent.Future<V>
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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 delegateFuture
that was supplied in thesetFuture
call.- Specified by:
cancel
in interfacejava.util.concurrent.Future<V>
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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.
- 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(java.lang.Runnable listener, java.util.concurrent.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: For fast, lightweight listeners that would be safe to execute in any thread, consider
MoreExecutors.directExecutor()
. Otherwise, avoid it. HeavyweightdirectExecutor
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, seeaddCallback()
.Memory consistency effects: Actions in a thread prior to adding a listener happen-before its execution begins, perhaps in another thread.
- Specified by:
addListener
in interfaceListenableFuture<V>
- Parameters:
listener
- the listener to run when the computation is completeexecutor
- the executor to run the listener in- Since:
- 10.0
- The listener may be executed by the caller of
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set
protected boolean set(@Nullable 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 by overridden by a call to aset*
method, only by a call tocancel(boolean)
.- 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
protected boolean setException(java.lang.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 by overridden by a call to aset*
method, only by a call tocancel(boolean)
.- 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
@Beta 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 by 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
.- 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 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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