Interface ChannelGroupFuture
- All Known Implementing Classes:
DefaultChannelGroupFuture
,VoidChannelGroupFuture
ChannelGroup
operation.
ChannelGroupFuture
is composed of ChannelFuture
s which
represent the outcome of the individual I/O operations that affect the
Channel
s 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(newChannelGroupFutureListener
() { 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.
-
Nested Class Summary
Nested classes/interfaces inherited from interface java.util.concurrent.Future
Future.State
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Method Summary
Modifier and TypeMethodDescriptionaddListener
(GenericFutureListener<? extends Future<? super Void>> listener) Adds the specified listener to this future.addListeners
(GenericFutureListener<? extends Future<? super Void>>... listeners) Adds the specified listeners to this future.await()
Waits for this future to be completed.Waits for this future to be completed without interruption.cause()
Returns the cause of the failed I/O operation if the I/O operation has failed.Returns theChannelFuture
of the individual I/O operation which is associated with the specifiedChannel
.group()
Returns theChannelGroup
which is associated with this future.boolean
Returnstrue
if and only if the I/O operations associated with this future have failed partially with some success.boolean
Returnstrue
if and only if the I/O operations associated with this future were partially successful with some failure.boolean
Returnstrue
if and only if all I/O operations associated with this future were successful without any failure.iterator()
Returns theIterator
that enumerates allChannelFuture
s which are associated with this future.removeListener
(GenericFutureListener<? extends Future<? super Void>> listener) Removes the first occurrence of the specified listener from this future.removeListeners
(GenericFutureListener<? extends Future<? super Void>>... listeners) Removes the first occurrence for each of the listeners from this future.sync()
Waits for this future until it is done, and rethrows the cause of the failure if this future failed.Waits for this future until it is done, and rethrows the cause of the failure if this future failed.Methods inherited from interface io.netty.util.concurrent.Future
await, await, awaitUninterruptibly, awaitUninterruptibly, cancel, getNow, isCancellable
Methods inherited from interface java.util.concurrent.Future
exceptionNow, get, get, isCancelled, isDone, resultNow, state
Methods inherited from interface java.lang.Iterable
forEach, spliterator
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Method Details
-
group
ChannelGroup group()Returns theChannelGroup
which is associated with this future. -
find
Returns theChannelFuture
of the individual I/O operation which is associated with the specifiedChannel
.- Returns:
- the matching
ChannelFuture
if found.null
otherwise.
-
isSuccess
boolean isSuccess()Returnstrue
if and only if all I/O operations associated with this future were successful without any failure. -
cause
ChannelGroupException cause()Description copied from interface:Future
Returns the cause of the failed I/O operation if the I/O operation has failed. -
isPartialSuccess
boolean isPartialSuccess()Returnstrue
if and only if the I/O operations associated with this future were partially successful with some failure. -
isPartialFailure
boolean isPartialFailure()Returnstrue
if and only if the I/O operations associated with this future have failed partially with some success. -
addListener
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 interfaceFuture<Void>
-
addListeners
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 interfaceFuture<Void>
-
removeListener
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 interfaceFuture<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 interfaceFuture<Void>
-
await
Description copied from interface:Future
Waits for this future to be completed.- Specified by:
await
in interfaceFuture<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 anInterruptedException
and discards it silently.- Specified by:
awaitUninterruptibly
in interfaceFuture<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 interfaceFuture<Void>
-
sync
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 interfaceFuture<Void>
- Throws:
InterruptedException
-
iterator
Iterator<ChannelFuture> iterator()Returns theIterator
that enumerates allChannelFuture
s which are associated with this future. Please note that the returnedIterator
is unmodifiable, which means aChannelFuture
cannot be removed from this future.- Specified by:
iterator
in interfaceIterable<ChannelFuture>
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