@DoNotMock(value="Use Futures.immediate*Future or SettableFuture") @GwtCompatible(emulated=true) public abstract class AbstractFuture<V> extends FluentFuture<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
afterDone()
, which will be invoked automatically when the future completes. 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.
|
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,
TimeUnit unit) |
protected void |
interruptTask()
Subclasses can override this method to implement interruption of the future's computation.
|
boolean |
isCancelled() |
boolean |
isDone() |
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 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). |
String |
toString() |
protected boolean |
wasInterrupted()
Returns true if this future was cancelled with
mayInterruptIfRunning set to true . |
addCallback, catching, catchingAsync, from, transform, transformAsync, withTimeout
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 during the call, even if the value is already available.
public V get() throws InterruptedException, ExecutionException
The default AbstractFuture
implementation throws InterruptedException
if the
current thread is interrupted during the call, even if the value is already available.
public boolean isDone()
public boolean isCancelled()
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.
Rather than override this method to perform additional cancellation work or cleanup,
subclasses should override afterDone()
, consulting isCancelled()
and 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)
.
protected void interruptTask()
cancel(true)
.
The default implementation does nothing.
This method is likely to be deprecated. Prefer to override afterDone()
, consulting
wasInterrupted()
to decide whether to interrupt your task.
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.
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 be overridden by a call to a set*
method, only by a call to cancel(boolean)
.value
- the value to be used as the resultFuture
protected 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 be 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 be 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.@Beta protected void afterDone()
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.
@Nullable protected String pendingToString()
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