Interface ChannelFuture
- All Known Implementing Classes:
AbstractChannel.ChannelCloseFuture
,ChannelRunnableWrapper
,CompleteChannelFuture
,DefaultChannelFuture
,FailedChannelFuture
,SslHandler.SSLEngineInboundCloseFuture
,SucceededChannelFuture
Channel
I/O operation.
All I/O operations in Netty are asynchronous. It means any I/O calls will
return immediately with no guarantee that the requested I/O operation has
been completed at the end of the call. Instead, you will be returned with
a ChannelFuture
instance which gives you the information about the
result or status of the I/O operation.
A ChannelFuture
is either uncompleted or completed.
When an I/O operation begins, a new future object is created. The new future
is uncompleted initially - it is neither succeeded, failed, nor cancelled
because the I/O operation is not finished yet. If the I/O operation is
finished either successfully, with failure, or by cancellation, the future is
marked as completed with more specific information, such as the cause of the
failure. Please note that even failure and cancellation belong to the
completed state.
+---------------------------+ | Completed successfully | +---------------------------+ +----> isDone() = true | +--------------------------+ | | isSuccess() = true | | Uncompleted | | +===========================+ +--------------------------+ | | Completed with failure | | isDone() = false | | +---------------------------+ | isSuccess() = false |----+----> isDone() = true | | isCancelled() = false | | | getCause() = non-null | | getCause() = null | | +===========================+ +--------------------------+ | | Completed by cancellation | | +---------------------------+ +----> isDone() = true | | isCancelled() = true | +---------------------------+Various methods are provided to let you check if the I/O operation has been completed, wait for the completion, and retrieve the result of the I/O operation. It also allows you to add
ChannelFutureListener
s so you
can get notified when the I/O operation is completed.
Prefer addListener(ChannelFutureListener)
to await()
It is recommended to prefer addListener(ChannelFutureListener)
to
await()
wherever possible to get notified when an I/O operation is
done and to do any follow-up tasks.
addListener(ChannelFutureListener)
is non-blocking. It simply adds
the specified ChannelFutureListener
to the ChannelFuture
, and
I/O thread will notify the listeners when the I/O operation associated with
the future is done. ChannelFutureListener
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 the operation is done. It is easier to implement
a sequential logic with await()
, but the caller thread blocks
unnecessarily until the I/O operation is 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 GoodByeMessage) {ChannelFuture
future = e.getChannel().close(); future.awaitUninterruptibly(); // Perform post-closure operation // ... } } // GOOD@Override
public void messageReceived(ChannelHandlerContext
ctx,MessageEvent
e) { if (e.getMessage() instanceof GoodByeMessage) {ChannelFuture
future = e.getChannel().close(); future.addListener(newChannelFutureListener
() { public void operationComplete(ChannelFuture
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.
Do not confuse I/O timeout and await timeout
The timeout value you specify withawait(long)
,
await(long, TimeUnit)
, awaitUninterruptibly(long)
, or
awaitUninterruptibly(long, TimeUnit)
are not related with I/O
timeout at all. If an I/O operation times out, the future will be marked as
'completed with failure,' as depicted in the diagram above. For example,
connect timeout should be configured via a transport-specific option:
// BAD - NEVER DO THISClientBootstrap
b = ...;ChannelFuture
f = b.connect(...); f.awaitUninterruptibly(10, TimeUnit.SECONDS); if (f.isCancelled()) { // Connection attempt cancelled by user } else if (!f.isSuccess()) { // You might get a NullPointerException here because the future // might not be completed yet. f.getCause().printStackTrace(); } else { // Connection established successfully } // GOODClientBootstrap
b = ...; // Configure the connect timeout option. b.setOption("connectTimeoutMillis", 10000);ChannelFuture
f = b.connect(...); f.awaitUninterruptibly(); // Now we are sure the future is completed. assert f.isDone(); if (f.isCancelled()) { // Connection attempt cancelled by user } else if (!f.isSuccess()) { f.getCause().printStackTrace(); } else { // Connection established successfully }
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Method Summary
Modifier and TypeMethodDescriptionvoid
addListener
(ChannelFutureListener listener) Adds the specified listener to this future.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
Waits for this future to be completed within the specified time limit.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, TimeUnit unit) Waits for this future to be completed within the specified time limit without interruption.boolean
cancel()
Cancels the I/O operation associated with this future and notifies all listeners if canceled successfully.getCause()
Returns the cause of the failed I/O operation if the I/O operation has failed.Returns a channel where the I/O operation associated with this future takes place.boolean
Returnstrue
if and only if this future was cancelled by acancel()
method.boolean
isDone()
Returnstrue
if and only if this future is complete, regardless of whether the operation was successful, failed, or cancelled.boolean
Returnstrue
if and only if the I/O operation was completed successfully.void
removeListener
(ChannelFutureListener listener) Removes the specified listener from this future.boolean
setFailure
(Throwable cause) Marks this future as a failure and notifies all listeners.boolean
setProgress
(long amount, long current, long total) Notifies the progress of the operation to the listeners that implementsChannelFutureProgressListener
.boolean
Marks this future as a success and notifies all listeners.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.
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Method Details
-
getChannel
Channel getChannel()Returns a channel where the I/O operation associated with this future takes place. -
isDone
boolean isDone()Returnstrue
if and only if this future is complete, regardless of whether the operation was successful, failed, or cancelled. -
isCancelled
boolean isCancelled()Returnstrue
if and only if this future was cancelled by acancel()
method. -
isSuccess
boolean isSuccess()Returnstrue
if and only if the I/O operation was completed successfully. -
getCause
Throwable getCause()Returns the cause of the failed I/O operation if the I/O operation has failed.- Returns:
- the cause of the failure.
null
if succeeded or this future is not completed yet.
-
cancel
boolean cancel()Cancels the I/O operation associated with this future and notifies all listeners if canceled successfully.- Returns:
true
if and only if the operation has been canceled.false
if the operation can't be canceled or is already completed.
-
setSuccess
boolean setSuccess()Marks this future as a success and notifies all listeners.- Returns:
true
if and only if successfully marked this future as a success. Otherwisefalse
because this future is already marked as either a success or a failure.
-
setFailure
Marks this future as a failure and notifies all listeners.- Returns:
true
if and only if successfully marked this future as a failure. Otherwisefalse
because this future is already marked as either a success or a failure.
-
setProgress
boolean setProgress(long amount, long current, long total) Notifies the progress of the operation to the listeners that implementsChannelFutureProgressListener
. Please note that this method will not do anything and returnfalse
if this future is complete already.- Returns:
true
if and only if notification was made.
-
addListener
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
Removes 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. -
sync
Waits for this future until it is done, and rethrows the cause of the failure if this future failed. If the cause of the failure is a checked exception, it is wrapped with a newChannelException
before being thrown.- Throws:
InterruptedException
-
syncUninterruptibly
ChannelFuture syncUninterruptibly()Waits for this future until it is done, and rethrows the cause of the failure if this future failed. If the cause of the failure is a checked exception, it is wrapped with a newChannelException
before being thrown. -
await
Waits for this future to be completed.- Throws:
InterruptedException
- if the current thread was interrupted
-
awaitUninterruptibly
ChannelFuture awaitUninterruptibly()Waits for this future to be completed without interruption. This method catches anInterruptedException
and discards it silently. -
await
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
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
Waits for this future to be completed within the specified time limit without interruption. This method catches anInterruptedException
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 anInterruptedException
and discards it silently.- Returns:
true
if and only if the future was completed within the specified time limit
-