org.jboss.netty.channel.group

Interface ChannelGroupFuture

All Superinterfaces:

java.lang.Iterable<ChannelFuture>

All Known Implementing Classes:

DefaultChannelGroupFuture

public interface ChannelGroupFuture
extends java.lang.Iterable<ChannelFuture>

The result of an asynchronous ChannelGroup operation. ChannelGroupFuture is composed of ChannelFutures 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(ChannelGroupFutureListener) to await()

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

addListener(ChannelGroupFutureListener) 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, 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 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 await() inside ChannelHandler

The event handler methods in ChannelHandler is often called by an I/O thread unless an ExecutionHandler is in the ChannelPipeline. If 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 await() can block the I/O operation it is waiting for, which is a dead lock.

 // BAD - NEVER DO THIS
  @Override
 public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
     if (e.getMessage() instanceof ShutdownMessage) {
         ChannelGroup allChannels = MyServer.getAllChannels();
         ChannelGroupFuture future = allChannels.close();
         future.awaitUninterruptibly();
         // Perform post-shutdown operation
         // ...
     }
 }

 // GOOD
  @Override
 public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
     if (e.getMessage() instanceof ShutdownMessage) {
         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 await(). In such a case, please make sure you do not call await() in an I/O thread. Otherwise, IllegalStateException will be raised to prevent a dead lock.

Method Summary

Modifier and Type	Method and Description
void	addListener(ChannelGroupFutureListener listener) Adds the specified listener to this future.
ChannelGroupFuture	await() Waits for this future to be completed.
boolean	await(long timeoutMillis) Waits for this future to be completed within the specified time limit.
boolean	await(long timeout, java.util.concurrent.TimeUnit unit) Waits for this future to be completed within the specified time limit.
ChannelGroupFuture	awaitUninterruptibly() Waits for this future to be completed without interruption.
boolean	awaitUninterruptibly(long timeoutMillis) Waits for this future to be completed within the specified time limit without interruption.
boolean	awaitUninterruptibly(long timeout, java.util.concurrent.TimeUnit unit) Waits for this future to be completed within the specified time limit without interruption.
ChannelFuture	find(Channel channel) Returns the ChannelFuture of the individual I/O operation which is associated with the specified Channel.
ChannelFuture	find(java.lang.Integer channelId) Returns the ChannelFuture of the individual I/O operation which is associated with the Channel whose ID matches the specified integer.
ChannelGroup	getGroup() Returns the ChannelGroup which is associated with this future.
boolean	isCompleteFailure() Returns true if and only if all I/O operations associated with this future have failed without any success.
boolean	isCompleteSuccess() Returns true if and only if all I/O operations associated with this future were successful without any failure.
boolean	isDone() Returns true if and only if this future is complete, regardless of whether the operation was successful, failed, or canceled.
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.
java.util.Iterator<ChannelFuture>	iterator() Returns the Iterator that enumerates all ChannelFutures which are associated with this future.
void	removeListener(ChannelGroupFutureListener listener) Removes the specified listener from this future.

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Method Detail

getGroup

ChannelGroup getGroup()

Returns the ChannelGroup which is associated with this future.

find

ChannelFuture find(java.lang.Integer channelId)

Returns the ChannelFuture of the individual I/O operation which is associated with the Channel whose ID matches the specified integer.

Returns:

the matching ChannelFuture if found. null otherwise.

find

ChannelFuture find(Channel channel)

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

Returns:

the matching ChannelFuture if found. null otherwise.

isDone

boolean isDone()

Returns true if and only if this future is complete, regardless of whether the operation was successful, failed, or canceled.

isCompleteSuccess

boolean isCompleteSuccess()

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

isPartialSuccess

boolean isPartialSuccess()

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

isCompleteFailure

boolean isCompleteFailure()

Returns true if and only if all I/O operations associated with this future have failed without any success.

isPartialFailure

boolean isPartialFailure()

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

addListener

void addListener(ChannelGroupFutureListener listener)

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.

removeListener

void removeListener(ChannelGroupFutureListener listener)

Removes the specified listener from this future. The specified listener is no longer notified when this future is done. If this future is already completed, this method has no effect and returns silently.

await

ChannelGroupFuture await()
                  throws java.lang.InterruptedException

Waits for this future to be completed.

Throws:

java.lang.InterruptedException - if the current thread was interrupted

awaitUninterruptibly

ChannelGroupFuture awaitUninterruptibly()

Waits for this future to be completed without interruption. This method catches an InterruptedException and discards it silently.

await

boolean await(long timeout,
              java.util.concurrent.TimeUnit unit)
       throws java.lang.InterruptedException

Waits for this future to be completed within the specified time limit.

Returns:

true if and only if the future was completed within the specified time limit

Throws:

java.lang.InterruptedException - if the current thread was interrupted

await

boolean await(long timeoutMillis)
       throws java.lang.InterruptedException

Waits for this future to be completed within the specified time limit.

Returns:

true if and only if the future was completed within the specified time limit

Throws:

java.lang.InterruptedException - if the current thread was interrupted

awaitUninterruptibly

boolean awaitUninterruptibly(long timeout,
                             java.util.concurrent.TimeUnit unit)

Waits for this future to be completed within the specified time limit without interruption. This method catches an InterruptedException and discards it silently.

Returns:

true if and only if the future was completed within the specified time limit

awaitUninterruptibly

boolean awaitUninterruptibly(long timeoutMillis)

Waits for this future to be completed within the specified time limit without interruption. This method catches an InterruptedException and discards it silently.

Returns:

true if and only if the future was completed within the specified time limit

iterator

java.util.Iterator<ChannelFuture> iterator()

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

Specified by:

iterator in interface java.lang.Iterable<ChannelFuture>