Interface ChannelGroupFuture

All Superinterfaces:
Future<Void>, Future<Void>, Iterable<ChannelFuture>
public interface ChannelGroupFuture extends Future<Void>, 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(GenericFutureListener) to await()

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

addListener(GenericFutureListener) 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. 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, ShutdownMessage msg) {
    ChannelGroup allChannels = MyServer.getAllChannels();
    ChannelGroupFuture future = allChannels.close();
    future.awaitUninterruptibly();
    // 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 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 Details

    • group

      ChannelGroup group()
      Returns the ChannelGroup which is associated with this future.

    • 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.

    • isSuccess

      boolean isSuccess()
      Returns true if and only if all I/O operations associated with this future were successful without any failure.
      Specified by:
      isSuccess in interface Future<Void>

    • cause

      ChannelGroupException cause()
      Description copied from interface: Future
      Returns the cause of the failed I/O operation if the I/O operation has failed.
      Specified by:
      cause in interface Future<Void>
      Returns:
      the cause of the failure. null if succeeded or this future is not completed yet.

    • 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(GenericFutureListener<? extends Future<? 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>

    • addListeners

      ChannelGroupFuture addListeners(GenericFutureListener<? extends Future<? super Void>>... listeners)
      Description copied from interface: Future
      Adds the specified listeners to this future. The specified listeners are notified when this future is done. If this future is already completed, the specified listeners are notified immediately.
      Specified by:
      addListeners in interface Future<Void>

    • removeListener

      ChannelGroupFuture removeListener(GenericFutureListener<? extends Future<? super Void>> listener)
      Description copied from interface: Future
      Removes the first occurrence of the specified listener from this future. The specified listener is no longer notified when this future is done. If the specified listener is not associated with this future, this method does nothing and returns silently.
      Specified by:
      removeListener in interface Future<Void>

    • removeListeners

      ChannelGroupFuture removeListeners(GenericFutureListener<? extends Future<? super Void>>... listeners)
      Description copied from interface: Future
      Removes the first occurrence for each of the listeners from this future. The specified listeners are no longer notified when this future is done. If the specified listeners are not associated with this future, this method does nothing and returns silently.
      Specified by:
      removeListeners in interface Future<Void>

    • await

      ChannelGroupFuture await() throws InterruptedException
      Description copied from interface: Future
      Waits for this future to be completed.
      Specified by:
      await in interface Future<Void>
      Throws:
      InterruptedException - if the current thread was interrupted

    • awaitUninterruptibly

      ChannelGroupFuture awaitUninterruptibly()
      Description copied from interface: Future
      Waits for this future to be completed without interruption. This method catches an InterruptedException and discards it silently.
      Specified by:
      awaitUninterruptibly in interface Future<Void>

    • syncUninterruptibly

      ChannelGroupFuture syncUninterruptibly()
      Description copied from interface: Future
      Waits for this future until it is done, and rethrows the cause of the failure if this future failed.
      Specified by:
      syncUninterruptibly in interface Future<Void>

    • sync

      ChannelGroupFuture sync() throws InterruptedException
      Description copied from interface: Future
      Waits for this future until it is done, and rethrows the cause of the failure if this future failed.
      Specified by:
      sync in interface Future<Void>
      Throws:
      InterruptedException

    • iterator

      Iterator<ChannelFuture> iterator()
      Returns the Iterator that enumerates all ChannelFutures which are associated with this future. Please note that the returned Iterator is unmodifiable, which means a ChannelFuture cannot be removed from this future.
      Specified by:
      iterator in interface Iterable<ChannelFuture>