@GwtCompatible public final class SettableFuture<V> extends AbstractFuture<V>
ListenableFuture
whose result can be set by a set(Object)
, setException(Throwable)
or setFuture(ListenableFuture)
call. It can also, like any
other Future
, be cancelled.
SettableFuture
is the recommended ListenableFuture
implementation when your
task cannot be implemented with ListeningExecutorService
, the various Futures
utility methods, or ListenableFutureTask
. Those APIs have less opportunity for developer
error. If your needs are more complex than SettableFuture
supports, use AbstractFuture
, which offers an extensible version of the API.
ValueFuture
)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)
Attempts to cancel execution of this task.
|
static <V> SettableFuture<V> |
create()
Creates a new
SettableFuture that can be completed or cancelled by a later method call. |
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.
|
boolean |
isCancelled()
Returns
true if this task was cancelled before it completed
normally. |
boolean |
isDone()
Returns
true if this task completed. |
boolean |
set(V value)
Sets the result of this
Future unless this Future has already been cancelled or
set (including set asynchronously). |
boolean |
setException(Throwable throwable)
Sets the failed result of this
Future unless this Future has already been
cancelled or set (including set asynchronously). |
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). |
afterDone, interruptTask, pendingToString, toString, tryInternalFastPathGetFailure, wasInterrupted
public static <V> SettableFuture<V> create()
SettableFuture
that can be completed or cancelled by a later method call.@CanIgnoreReturnValue public boolean set(V value)
AbstractFuture
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 AbstractFuture.cancel(boolean)
.set
in class AbstractFuture<V>
value
- the value to be used as the resultFuture
@CanIgnoreReturnValue public boolean setException(Throwable throwable)
AbstractFuture
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 AbstractFuture.cancel(boolean)
.setException
in class AbstractFuture<V>
throwable
- the exception to be used as the failed resultFuture
@CanIgnoreReturnValue public boolean setFuture(ListenableFuture<? extends V> future)
AbstractFuture
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 AbstractFuture.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 AbstractFuture.interruptTask()
method, and the AbstractFuture.wasInterrupted()
method will not
return true
.
setFuture
in class AbstractFuture<V>
future
- the future to delegate toFuture
was not previously
cancelled or set.@CanIgnoreReturnValue public final V get() throws InterruptedException, ExecutionException
AbstractFuture
The default AbstractFuture
implementation throws InterruptedException
if the
current thread is interrupted during the call, even if the value is already available.
get
in interface Future<V>
get
in class AbstractFuture<V>
InterruptedException
- if the current thread was interrupted
while waitingExecutionException
- if the computation threw an
exception@CanIgnoreReturnValue public final V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
AbstractFuture
The default AbstractFuture
implementation throws InterruptedException
if the
current thread is interrupted during the call, even if the value is already available.
get
in interface Future<V>
get
in class AbstractFuture<V>
timeout
- the maximum time to waitunit
- the time unit of the timeout argumentInterruptedException
- if the current thread was interrupted
while waitingExecutionException
- if the computation threw an
exceptionTimeoutException
- if the wait timed outpublic final boolean isDone()
java.util.concurrent.Future
true
if this task completed.
Completion may be due to normal termination, an exception, or
cancellation -- in all of these cases, this method will return
true
.isDone
in interface Future<V>
isDone
in class AbstractFuture<V>
true
if this task completedpublic final boolean isCancelled()
java.util.concurrent.Future
true
if this task was cancelled before it completed
normally.isCancelled
in interface Future<V>
isCancelled
in class AbstractFuture<V>
true
if this task was cancelled before it completedpublic final void addListener(Runnable listener, Executor executor)
AbstractFuture
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.
Guava implementations of ListenableFuture
promptly release references to listeners
after executing them.
addListener
in interface ListenableFuture<V>
addListener
in class AbstractFuture<V>
listener
- the listener to run when the computation is completeexecutor
- the executor to run the listener in@CanIgnoreReturnValue public final boolean cancel(boolean mayInterruptIfRunning)
AbstractFuture
cancel
is called,
this task should never run. If the task has already started,
then the mayInterruptIfRunning
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 return true
. Subsequent calls to Future.isCancelled()
will always return true
if this method returned true
.
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 AbstractFuture.afterDone()
, consulting AbstractFuture.isCancelled()
and AbstractFuture.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)
.
cancel
in interface Future<V>
cancel
in class AbstractFuture<V>
mayInterruptIfRunning
- true
if the thread executing this
task should be interrupted; otherwise, in-progress tasks are allowed
to completefalse
if the task could not be cancelled,
typically because it has already completed normally;
true
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