@GwtCompatible(emulated=true) public abstract class AbstractFuture<V> extends com.google.common.util.concurrent.internal.InternalFutureFailureAccess 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
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)
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()
Returns
true if this task was cancelled before it completed
normally. |
boolean |
isDone()
Returns
true 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 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()
Returns a string representation of the object.
|
protected Throwable |
tryInternalFastPathGetFailure()
Usually returns
null but, if this Future has failed, may optionally
return the cause of the failure. |
protected boolean |
wasInterrupted()
Returns true if this future was cancelled with
mayInterruptIfRunning set to true. |
protected AbstractFuture()
@CanIgnoreReturnValue 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.
get in interface Future<V>timeout - the maximum time to waitunit - the time unit of the timeout argumentCancellationException - if the computation was cancelledInterruptedException - if the current thread was interrupted
while waitingTimeoutException - if the wait timed outExecutionException - if the computation threw an
exception@CanIgnoreReturnValue 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.
get in interface Future<V>CancellationException - if the computation was cancelledInterruptedException - if the current thread was interrupted
while waitingExecutionException - if the computation threw an
exceptionpublic boolean isDone()
java.util.concurrent.Futuretrue 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.public boolean isCancelled()
java.util.concurrent.Futuretrue if this task was cancelled before it completed
normally.isCancelled in interface Future<V>true if this task was cancelled before it completed@CanIgnoreReturnValue public boolean cancel(boolean mayInterruptIfRunning)
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 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).
cancel in interface Future<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 otherwiseprotected 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.
addListener in interface ListenableFuture<V>listener - the listener to run when the computation is completeexecutor - the executor to run the listener in@CanIgnoreReturnValue protected boolean set(@NullableDecl 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@CanIgnoreReturnValue 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 @CanIgnoreReturnValue 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.
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 the wasInterrupted() method will not
return true.
future - the future to delegate toFuture was not previously
cancelled or set.@Beta @ForOverride 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.
@NullableDecl protected final Throwable tryInternalFastPathGetFailure()
null but, if this Future 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 return true
isCancelled() must return false
get() must not block, and it must throw an ExecutionException with the
return value of this method as its cause
This method is protected so that classes like com.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, call InternalFutures.tryInternalFastPathGetFailure(InternalFutureFailureAccess).
tryInternalFastPathGetFailure in class com.google.common.util.concurrent.internal.InternalFutureFailureAccesspublic String toString()
java.lang.ObjecttoString 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 class Object
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())
@NullableDecl protected String pendingToString()
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