Interface ChannelGroupFuture

All Superinterfaces:
Iterable<ChannelFuture>
All Known Implementing Classes:
DefaultChannelGroupFuture
public interface ChannelGroupFuture extends 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 Details

    • getGroup

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

    • find

      ChannelFuture find(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 InterruptedException
      Waits for this future to be completed.
      Throws:
      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, TimeUnit unit) throws 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:
      InterruptedException - if the current thread was interrupted

    • await

      boolean await(long timeoutMillis) throws 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:
      InterruptedException - if the current thread was interrupted

    • awaitUninterruptibly

      boolean awaitUninterruptibly(long timeout, 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

      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 Iterable<ChannelFuture>