public abstract class AbstractFuture<V> extends Objectimplements ListenableFuture <V>
ListenableFuture interface. This class is preferable to
FutureTask for two reasons: It implements
ListenableFuture, and it does not implement
Runnable. (If you want a
Runnable implementation of
ListenableFuture, create a
ListenableFutureTask, or submit your tasks to a
ListeningExecutorService.)
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) and setException(Throwable). Subclasses may also override interruptTask(), which will be invoked automatically if a call to cancel(true) succeeds in canceling the future.
AbstractFuture uses an AbstractQueuedSynchronizer to deal with concurrency issues and guarantee thread safety.
The state changing methods all return a boolean indicating success or failure in changing the future's state. Valid states are running, completed, failed, or cancelled.
This class uses an ExecutionList to guarantee that all registered listeners will be executed, either when the future finishes or, for listeners that are added after the future completes, immediately. Runnable-Executor pairs are stored in the execution list but are not necessarily executed in the order in which they were added. (If a listener is added after the Future is complete, it will be executed immediately, even if earlier listeners have not been executed. Additionally, executors need not guarantee FIFO execution, or different listeners may run in different executors.)
| Modifier | Constructor and Description |
|---|---|
protected |
AbstractFuture()
Constructor for use by subclasses.
|
| Modifier and Type | Method and Description |
|---|---|
void |
addListener(Runnable
Registers a listener to be
run on the given executor.
|
boolean |
cancel(boolean mayInterruptIfRunning)
|
V |
get()
|
V |
get(long timeout, TimeUnit
|
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)
Subclasses should invoke this method to set the result of the computation to
value.
|
protected boolean |
setException(Throwable
Subclasses should invoke this method to set the result of the computation to an error,
throwable.
|
protected boolean |
wasInterrupted()
Returns true if this future was cancelled with
mayInterruptIfRunning set to
true.
|
public V get(long timeout, TimeUnitunit) 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).
CancellationException -
TimeoutException
ExecutionException
public 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).
CancellationException -
ExecutionException
public boolean isDone()
public boolean isCancelled()
public boolean cancel(boolean mayInterruptIfRunning)
protected void interruptTask()
cancel(true).
The default implementation does nothing.
protected final boolean wasInterrupted()
mayInterruptIfRunning set to
true.
public void addListener(Runnablelistener, Executor exec)
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. For heavier listeners, directExecutor() carries some caveats. For example, the listener may run on an unpredictable or undesirable thread:
Future is done at the time addListener is called, addListener will execute the listener inline. Future is not yet done, addListener will schedule the listener to be run by the thread that completes this Future, which may be an internal system thread such as an RPC network thread. Also note that, regardless of which thread executes the directExecutor() listener, all other registered but unexecuted listeners are prevented from running during its execution, even if those listeners are to run in other executors.
This is the most general listener interface. For common operations performed using listeners, see Futures. For a simplified but general listener interface, see addCallback().
addListener in interface
ListenableFuture<V>
listener - the listener to run when the computation is complete
exec - the executor to run the listener in
protected boolean set(V value)
value. This will set the state of the future to
AbstractFuture.Sync.COMPLETED and invoke the listeners if the state was successfully changed.
value - the value that was the result of the task.
protected boolean setException(Throwablethrowable)
throwable. This will set the state of the future to
AbstractFuture.Sync.COMPLETED and invoke the listeners if the state was successfully changed.
throwable - the exception that the task failed with.