@GwtCompatible(emulated=true) public abstract class AbstractFuture<V> extends Object implements ListenableFuture<V>
ListenableFuture, intended for advanced users only. More
common ways to create a ListenableFuture include instantiating a SettableFuture,
submitting a task to a ListeningExecutorService, and deriving a Future from an
existing one, typically using methods like Futures.transform and Futures.catching.
This class implements all methods in ListenableFuture. Subclasses should provide a way
to set the result of the computation through the protected methods set(Object), setFuture(ListenableFuture) and setException(Throwable). Subclasses may also override
interruptTask(), which will be invoked automatically if a call to cancel(true) succeeds in canceling the future. Subclasses should rarely
override other methods.
| Modifier | Constructor and Description |
|---|---|
protected |
AbstractFuture()
Constructor for use by subclasses.
|
| Modifier and Type | Method and Description |
|---|---|
void |
addListener(Runnable listener,
Executor executor)
Registers a listener to be run on
the given executor.
|
boolean |
cancel(boolean mayInterruptIfRunning) |
V |
get() |
V |
get(long timeout,
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 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). |
protected boolean |
wasInterrupted()
Returns true if this future was cancelled with
mayInterruptIfRunning set to true. |
protected AbstractFuture()
public V get(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException, ExecutionException
The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted before or during
the call, even if the value is already available.
get in interface Future<V>InterruptedException - if the current thread was interrupted before
or during the call (optional but recommended).CancellationExceptionTimeoutExceptionExecutionExceptionpublic V get() throws InterruptedException, ExecutionException
The default AbstractFuture implementation throws InterruptedException if the current thread is interrupted before or during
the call, even if the value is already available.
get in interface Future<V>InterruptedException - if the current thread was interrupted before
or during the call (optional but recommended).CancellationExceptionExecutionExceptionpublic boolean isCancelled()
isCancelled in interface Future<V>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.
protected void interruptTask()
cancel(true).
The default implementation does nothing.
protected final boolean wasInterrupted()
mayInterruptIfRunning set to true.public void addListener(Runnable listener, Executor executor)
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:
addListener. That
caller may be a UI thread or other latency-sensitive thread. This can harm
UI responsiveness.
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.
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.
addListener in interface ListenableFuture<V>listener - the listener to run when the computation is completeexecutor - the executor to run the listener inprotected boolean set(@Nullable V value)
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 by overridden by a call to a set*
method, only by a call to cancel(boolean).value - the value to be used as the resultFutureprotected boolean setException(Throwable throwable)
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 by overridden by a call to a set*
method, only by a call to cancel(boolean).throwable - the exception to be used as the failed resultFuture@Beta protected boolean setFuture(ListenableFuture<? extends V> future)
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 by 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.
future - the future to delegate toFuture was not previously
cancelled or set.Copyright © 2010-2015. All Rights Reserved.