Module io.netty5.transport

Package io.netty5.channel.group

Interface ChannelGroupFuture

All Superinterfaces:

Future<Void>, Iterable<Future<Void>>

public interface ChannelGroupFuture
extends Future<Void>, Iterable<Future<Void>>

The result of an asynchronous ChannelGroup operation. ChannelGroupFuture is composed of Futures which represent the outcome of the individual I/O operations that affect the Channels in the ChannelGroup.

All I/O operations in ChannelGroup are asynchronous. It means any I/O calls will return immediately with no guarantee that the requested I/O operations have been completed at the end of the call. Instead, you will be returned with a ChannelGroupFuture instance which tells you when the requested I/O operations have succeeded, failed, or cancelled.

Various methods are provided to let you check if the I/O operations has been completed, wait for the completion, and retrieve the result of the I/O operation. It also allows you to add more than one ChannelGroupFutureListener so you can get notified when the I/O operation have been completed.

Prefer addListener(FutureListener) to FutureCompletionStage.await()

It is recommended to prefer addListener(FutureListener) to FutureCompletionStage.await() wherever possible to get notified when I/O operations are done and to do any follow-up tasks.

addListener(FutureListener) is non-blocking. It simply adds the specified ChannelGroupFutureListener to the ChannelGroupFuture, and I/O thread will notify the listeners when the I/O operations associated with the future is done. ChannelGroupFutureListener yields the best performance and resource utilization because it does not block at all, but it could be tricky to implement a sequential logic if you are not used to event-driven programming.

By contrast, FutureCompletionStage.await() is a blocking operation. Once called, the caller thread blocks until all I/O operations are done. It is easier to implement a sequential logic with FutureCompletionStage.await(), but the caller thread blocks unnecessarily until all I/O operations are done and there's relatively expensive cost of inter-thread notification. Moreover, there's a chance of dead lock in a particular circumstance, which is described below.

Do not call FutureCompletionStage.await() inside ChannelHandler

The event handler methods in ChannelHandler is often called by an I/O thread. If FutureCompletionStage.await() is called by an event handler method, which is called by the I/O thread, the I/O operation it is waiting for might never be complete because FutureCompletionStage.await() can block the I/O operation it is waiting for, which is a deadlock.

 // BAD - NEVER DO THIS
 @Override
 public void messageReceived(ChannelHandlerContext ctx, ShutdownMessage msg) {
     ChannelGroup allChannels = MyServer.getAllChannels();
     ChannelGroupFuture future = allChannels.close();
     future.asStage().await();
     // Perform post-shutdown operation
     // ...

 }

 // GOOD
 @Override
 public void messageReceived(ChannelHandlerContext ctx, ShutdownMessage msg) {
     ChannelGroup allChannels = MyServer.getAllChannels();
     ChannelGroupFuture future = allChannels.close();
     future.addListener(new ChannelGroupFutureListener() {
         public void operationComplete(ChannelGroupFuture future) {
             // Perform post-closure operation
             // ...
         }
     });
 }
 

In spite of the disadvantages mentioned above, there are certainly the cases where it is more convenient to call FutureCompletionStage.await(). In such a case, please make sure you do not call FutureCompletionStage.await() in an I/O thread. Otherwise, IllegalStateException will be raised to prevent a dead lock.

Method Summary

Modifier and Type	Method	Description
ChannelGroupFuture	addListener(FutureListener<? super Void> listener)	Adds the specified listener to this future.
boolean	cancel()	Cancel this asynchronous operation, unless it has already been completed or is not cancellable.
ChannelGroupException	cause()
EventExecutor	executor()	Returns the EventExecutor that is tied to this Promise or Future.
Future<Void>	find(Channel channel)	Returns the Future of the individual I/O operation which is associated with the specified Channel.
V	getNow()	Return the successful result of this asynchronous operation, if any.
ChannelGroup	group()	Returns the ChannelGroup which is associated with this future.
boolean	isCancellable()	Returns true if and only if the operation can be cancelled via cancel().
boolean	isCancelled()	Return true if this operation has been cancelled.
boolean	isDone()	Return true if this operation has been completed either successfully, unsuccessfully, or through cancellation.
boolean	isFailed()	Returns true if and only if the operation was completed and failed.
boolean	isPartialFailure()	Returns true if and only if the I/O operations associated with this future have failed partially with some success.
boolean	isPartialSuccess()	Returns true if and only if the I/O operations associated with this future were partially successful with some failure.
boolean	isSuccess()	Returns true if and only if all I/O operations associated with this future were successful without any failure.
Iterator<Future<Void>>	iterator()	Returns the Iterator that enumerates all Futures which are associated with this future.

Methods inherited from interface io.netty5.util.concurrent.Future

addListener, asStage, cascadeTo, flatMap, map

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Method Detail

group

ChannelGroup group()

Returns the ChannelGroup which is associated with this future.

find

Future<Void> find(Channel channel)

Returns the Future of the individual I/O operation which is associated with the specified Channel.

Returns:

the matching Future if found. null otherwise.

isSuccess

boolean isSuccess()

Returns true if and only if all I/O operations associated with this future were successful without any failure.

cause

ChannelGroupException cause()

isPartialSuccess

boolean isPartialSuccess()

Returns true if and only if the I/O operations associated with this future were partially successful with some failure.

isPartialFailure

boolean isPartialFailure()

Returns true if and only if the I/O operations associated with this future have failed partially with some success.

addListener

ChannelGroupFuture addListener(FutureListener<? super Void> listener)

Description copied from interface: Future

Adds the specified listener to this future. The specified listener is notified when this future is done. If this future is already completed, the specified listener is notified immediately.

Specified by:

addListener in interface Future<Void>

Parameters:

listener - The listener to be called when this future completes. The listener will be passed this future as an argument.

Returns:

this future object.

iterator

Iterator<Future<Void>> iterator()

Returns the Iterator that enumerates all Futures which are associated with this future. Please note that the returned Iterator is is unmodifiable, which means a Future cannot be removed from this future.

Specified by:

iterator in interface Iterable<Future<Void>>

cancel

boolean cancel()

Cancel this asynchronous operation, unless it has already been completed or is not cancellable.

A cancelled operation is considered to be done and failed.

If the cancellation was successful, the result of this operation will be that it has failed with a CancellationException.

Cancellation will not cause any threads working on the operation to be interrupted.

Returns:

true if the operation was cancelled by this call, otherwise false.

isFailed

boolean isFailed()

Returns true if and only if the operation was completed and failed.

isCancelled

boolean isCancelled()

Return true if this operation has been cancelled.

Returns:

true if this operation has been cancelled, otherwise false.

isDone

boolean isDone()

Return true if this operation has been completed either successfully, unsuccessfully, or through cancellation.

Returns:

true if this operation has completed, otherwise false.

isCancellable

boolean isCancellable()

Returns true if and only if the operation can be cancelled via cancel(). Note that this is inherently racy, as the operation could be made uncancellable at any time.

Returns:

true if this operation can be cancelled.

getNow

V getNow()

Return the successful result of this asynchronous operation, if any. If the operation has not yet been completed, then this will throw IllegalStateException. If the operation has been cancelled or failed with an exception, then this returns null. Note that asynchronous operations can also be completed successfully with a null result.

Returns:

the result of this operation, if completed successfully.

Throws:

IllegalStateException - if this Future or Promise has not completed yet.

executor

EventExecutor executor()

Returns the EventExecutor that is tied to this Promise or Future.