Package org.apache.hadoop.hdfs.server.datanode.checker

Class AbstractFuture<V>

java.lang.Object

org.apache.hadoop.hdfs.server.datanode.checker.AbstractFuture<V>

All Implemented Interfaces:

java.util.concurrent.Future<V>, org.apache.hadoop.thirdparty.com.google.common.util.concurrent.ListenableFuture<V>

@GwtCompatible(emulated=true)
public abstract class AbstractFuture<V>
extends java.lang.Object
implements org.apache.hadoop.thirdparty.com.google.common.util.concurrent.ListenableFuture<V>

An abstract implementation of 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 (ListenableFuture, org.apache.hadoop.thirdparty.com.google.common.base.Function) Futures.transform and its overloaded versions.

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 interruptTask(), which will be invoked automatically if a call to cancel(true) succeeds in canceling the future. Subclasses should rarely override other methods.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractFuture()	Constructor for use by subclasses.

Method Summary

Modifier and Type	Method	Description
void	addListener(java.lang.Runnable listener, java.util.concurrent.Executor executor)
protected void	afterDone()	Callback method that is called exactly once after the future is completed.
boolean	cancel(boolean mayInterruptIfRunning)
static java.util.concurrent.Executor	directExecutor()	Returns an Executor that runs each task in the thread that invokes execute, as in ThreadPoolExecutor.CallerRunsPolicy.
V	get()
V	get(long timeout, java.util.concurrent.TimeUnit unit)
static <V> V	getDone(java.util.concurrent.Future<V> future)
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)	Sets the result of this Future unless this Future has already been cancelled or set (including set asynchronously).
protected boolean	setException(java.lang.Throwable throwable)	Sets the failed result of this Future unless this Future has already been cancelled or set (including set asynchronously).
protected boolean	setFuture(org.apache.hadoop.thirdparty.com.google.common.util.concurrent.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).
protected boolean	wasInterrupted()	Returns true if this future was cancelled with mayInterruptIfRunning set to true.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AbstractFuture

protected AbstractFuture()

Constructor for use by subclasses.

Method Detail

get

public V get(long timeout,
             java.util.concurrent.TimeUnit unit)
      throws java.lang.InterruptedException,
             java.util.concurrent.TimeoutException,
             java.util.concurrent.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.

Specified by:

get in interface java.util.concurrent.Future<V>

Throws:

java.lang.InterruptedException - if the current thread was interrupted before or during the call (optional but recommended).

java.util.concurrent.CancellationException

java.util.concurrent.TimeoutException

java.util.concurrent.ExecutionException

get

public V get()
      throws java.lang.InterruptedException,
             java.util.concurrent.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.

Specified by:

get in interface java.util.concurrent.Future<V>

Throws:

java.lang.InterruptedException - if the current thread was interrupted before or during the call (optional but recommended).

java.util.concurrent.CancellationException

java.util.concurrent.ExecutionException

isDone

public boolean isDone()

Specified by:

isDone in interface java.util.concurrent.Future<V>

isCancelled

public boolean isCancelled()

Specified by:

isCancelled in interface java.util.concurrent.Future<V>

cancel

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.

Specified by:

cancel in interface java.util.concurrent.Future<V>

interruptTask

protected void interruptTask()

Subclasses can override this method to implement interruption of the future's computation. The method is invoked automatically by a successful call to cancel(true).

The default implementation does nothing.

Since:

10.0

wasInterrupted

protected final boolean wasInterrupted()

Returns true if this future was cancelled with mayInterruptIfRunning set to true.

Since:

14.0

addListener

public void addListener(java.lang.Runnable listener,
                        java.util.concurrent.Executor executor)

Specified by:

addListener in interface org.apache.hadoop.thirdparty.com.google.common.util.concurrent.ListenableFuture<V>

Since:

10.0

set

protected boolean set(@Nullable
                      V value)

Sets the result of this 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).

Parameters:

value - the value to be used as the result

Returns:

true if the attempt was accepted, completing the Future

setException

protected boolean setException(java.lang.Throwable throwable)

Sets the failed result of this 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).

Parameters:

throwable - the exception to be used as the failed result

Returns:

true if the attempt was accepted, completing the Future

setFuture

@Beta
protected boolean setFuture(org.apache.hadoop.thirdparty.com.google.common.util.concurrent.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).

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.

Parameters:

future - the future to delegate to

Returns:

true if the attempt was accepted, indicating that the Future was not previously cancelled or set.

Since:

19.0

getDone

public static <V> V getDone(java.util.concurrent.Future<V> future)
                     throws java.util.concurrent.ExecutionException

Throws:

java.util.concurrent.ExecutionException

afterDone

@Beta
protected void afterDone()

Callback method that is called exactly once after the future is completed.

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.

Since:

20.0

directExecutor

public static java.util.concurrent.Executor directExecutor()

Returns an Executor that runs each task in the thread that invokes execute, as in ThreadPoolExecutor.CallerRunsPolicy.

This instance is equivalent to:

   
   final class DirectExecutor implements Executor {
     public void execute(Runnable r) {
       r.run();
     }
   }