Interface ChannelFuture
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- All Known Implementing Classes:
ChannelRunnableWrapper
,CompleteChannelFuture
,DefaultChannelFuture
,FailedChannelFuture
,SucceededChannelFuture
public interface ChannelFuture
The result of an asynchronousChannel
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 addChannelFutureListener
s so you can get notified when the I/O operation is completed.Prefer
It is recommended to preferaddListener(ChannelFutureListener)
toawait()
addListener(ChannelFutureListener)
toawait()
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 specifiedChannelFutureListener
to theChannelFuture
, 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 withawait()
, 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()
insideChannelHandler
The event handler methods in
ChannelHandler
is often called by an I/O thread unless anExecutionHandler
is in theChannelPipeline
. Ifawait()
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 becauseawait()
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 callawait()
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)
, orawaitUninterruptibly(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 THIS
ClientBootstrap
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
All Methods Instance Methods Abstract Methods Modifier and Type Method Description void
addListener(ChannelFutureListener listener)
Adds the specified listener to this future.ChannelFuture
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, TimeUnit unit)
Waits for this future to be completed within the specified time limit.ChannelFuture
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, 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.Throwable
getCause()
Returns the cause of the failed I/O operation if the I/O operation has failed.Channel
getChannel()
Returns a channel where the I/O operation associated with this future takes place.boolean
isCancelled()
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
isSuccess()
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
setSuccess()
Marks this future as a success and notifies all listeners.ChannelFuture
sync()
Waits for this future until it is done, and rethrows the cause of the failure if this future failed.ChannelFuture
syncUninterruptibly()
Waits for this future until it is done, and rethrows the cause of the failure if this future failed.
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Method Detail
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getChannel
Channel getChannel()
Returns a channel where the I/O operation associated with this future takes place.
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isDone
boolean isDone()
Returnstrue
if and only if this future is complete, regardless of whether the operation was successful, failed, or cancelled.
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isCancelled
boolean isCancelled()
Returnstrue
if and only if this future was cancelled by acancel()
method.
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isSuccess
boolean isSuccess()
Returnstrue
if and only if the I/O operation was completed successfully.
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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.
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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.
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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.
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setFailure
boolean setFailure(Throwable cause)
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.
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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.
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addListener
void addListener(ChannelFutureListener 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.
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removeListener
void removeListener(ChannelFutureListener listener)
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.
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sync
ChannelFuture sync() throws InterruptedException
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
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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.
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await
ChannelFuture await() throws InterruptedException
Waits for this future to be completed.- Throws:
InterruptedException
- if the current thread was interrupted
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awaitUninterruptibly
ChannelFuture awaitUninterruptibly()
Waits for this future to be completed without interruption. This method catches anInterruptedException
and discards it silently.
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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
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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
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awaitUninterruptibly
boolean awaitUninterruptibly(long timeout, TimeUnit unit)
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
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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
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