@CanIgnoreReturnValue @GwtCompatible public abstract class ForwardingListenableFuture<V> extends ForwardingFuture<V> implements ListenableFuture<V>
ListenableFuturewhich forwards all its method calls to another future. Subclasses should override one or more methods to modify the behavior of the backing future as desired per the decorator pattern.
Most subclasses can just use
|Modifier and Type||Class and Description|
|Modifier||Constructor and Description|
Constructor for use by subclasses.
|Modifier and Type||Method and Description|
Registers a listener to be run on the given executor.
Returns the backing delegate instance that methods are forwarded to.
cancel, get, get, isCancelled, isDone
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
protected abstract ListenableFuture<? extends V> delegate()
ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.
public void addListener(Runnable listener, 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
Executor.execute (e.g., a
RejectedExecutionException or an exception
thrown by direct execution) will be caught and
Note: For fast, lightweight listeners that would be safe to execute in any thread, consider
MoreExecutors.directExecutor(). Otherwise, avoid it. Heavyweight
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.
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.
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