Package org.jboss.netty.handler.queue
Class BufferedWriteHandler
java.lang.Object
org.jboss.netty.channel.SimpleChannelHandler
org.jboss.netty.handler.queue.BufferedWriteHandler
- All Implemented Interfaces:
ChannelDownstreamHandler
,ChannelHandler
,ChannelUpstreamHandler
,LifeCycleAwareChannelHandler
public class BufferedWriteHandler
extends SimpleChannelHandler
implements LifeCycleAwareChannelHandler
Emulates buffered write operation. This handler stores all write requests
into an unbounded
Queue
and flushes them to the downstream when
flush()
method is called.
Here is an example that demonstrates the usage:
BufferedWriteHandler bufferedWriter = new BufferedWriteHandler(); ChannelPipeline p = ...; p.addFirst("buffer", bufferedWriter); ... Channel ch = ...; // msg1, 2, and 3 are stored in the queue of bufferedWriter. ch.write(msg1); ch.write(msg2); ch.write(msg3); // and will be flushed on request. bufferedWriter.flush();
Auto-flush
The write request queue is automatically flushed when the associatedChannel
is disconnected or closed. However, it does not flush the
queue otherwise. It means you have to call flush()
before the size
of the queue increases too much. You can implement your own auto-flush
strategy by extending this handler:
public class AutoFlusher extendsBufferedWriteHandler
{ private final AtomicLong bufferSize = new AtomicLong(); @Override public void writeRequested(ChannelHandlerContext
ctx,MessageEvent
e) { super.writeRequested(ctx, e);ChannelBuffer
data = (ChannelBuffer
) e.getMessage(); int newBufferSize = bufferSize.addAndGet(data.readableBytes()); // Flush the queue if it gets larger than 8KiB. if (newBufferSize > 8192) { flush(); bufferSize.set(0); } } }
Consolidate on flush
If there are two or more write requests in the queue and all their message type isChannelBuffer
, they can be merged into a single write request
to save the number of system calls.
BEFORE consolidation: AFTER consolidation: +-------+-------+-------+ +-------------+ | Req C | Req B | Req A |------\\| Request ABC | | "789" | "456" | "123" |------//| "123456789" | +-------+-------+-------+ +-------------+This feature is disabled by default. You can override the default when you create this handler or call
flush(boolean)
. If you specified
true
when you call the constructor, calling flush()
will
always consolidate the queue. Otherwise, you have to call
flush(boolean)
with true
to enable this feature for each
flush.
The disadvantage of consolidation is that the ChannelFuture
and its
ChannelFutureListener
s associated with the original write requests
might be notified later than when they are actually written out. They will
always be notified when the consolidated write request is fully written.
The following example implements the consolidation strategy that reduces the number of write requests based on the writability of a channel:
public class ConsolidatingAutoFlusher extendsBufferedWriteHandler
{ public ConsolidatingAutoFlusher() { // Enable consolidation by default. super(true); } @Override public void channelOpen(ChannelHandlerContext
ctx,ChannelStateEvent
e) throws Exception {ChannelConfig
cfg = e.getChannel().getConfig(); if (cfg instanceofNioSocketChannelConfig
) { // Lower the watermark to increase the chance of consolidation. cfg.setWriteBufferLowWaterMark(0); } super.channelOpen(e); } @Override public void writeRequested(ChannelHandlerContext
ctx,MessageEvent
e) throws Exception { super.writeRequested(ctx, et); if (e.getChannel().isWritable()) { flush(); } } @Override public void channelInterestChanged(ChannelHandlerContext
ctx,ChannelStateEvent
e) throws Exception { if (e.getChannel().isWritable()) { flush(); } } }
Prioritized Writes
You can implement prioritized writes by specifying an unbounded priority queue in the constructor of this handler. It will be required to design the proper strategy to determine how oftenflush()
should be called.
For example, you could call flush()
periodically, using
HashedWheelTimer
every second.-
Nested Class Summary
Nested classes/interfaces inherited from interface org.jboss.netty.channel.ChannelHandler
ChannelHandler.Sharable
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate final boolean
private ChannelHandlerContext
private final AtomicBoolean
private final Queue<MessageEvent>
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Constructor Summary
ConstructorsConstructorDescriptionCreates a new instance with the default unboundedBlockingQueue
implementation and without buffer consolidation.BufferedWriteHandler
(boolean consolidateOnFlush) Creates a new instance withConcurrentLinkedQueue
BufferedWriteHandler
(Queue<MessageEvent> queue) Creates a new instance with the specified thread-safe unboundedQueue
and without buffer consolidation.BufferedWriteHandler
(Queue<MessageEvent> queue, boolean consolidateOnFlush) Creates a new instance with the specified thread-safe unboundedQueue
. -
Method Summary
Modifier and TypeMethodDescriptionvoid
void
Fail all buffered writes that are left.void
void
void
Fail all buffered writes that are left.void
Invoked whenChannel.close()
was called.private List<MessageEvent>
consolidatedWrite
(List<MessageEvent> pendingWrites) void
Invoked whenChannel.disconnect()
was called.void
flush()
Sends the queued write requests to the downstream.void
flush
(boolean consolidateOnFlush) Sends the queued write requests to the downstream.protected Queue<MessageEvent>
getQueue()
Returns the queue which stores the write requests.boolean
void
Stores all write requests to the queue so that they are actually written onflush()
.Methods inherited from class org.jboss.netty.channel.SimpleChannelHandler
bindRequested, channelBound, channelConnected, channelDisconnected, channelInterestChanged, channelOpen, channelUnbound, childChannelClosed, childChannelOpen, connectRequested, exceptionCaught, handleDownstream, handleUpstream, messageReceived, setInterestOpsRequested, unbindRequested, writeComplete
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Field Details
-
queue
-
consolidateOnFlush
private final boolean consolidateOnFlush -
ctx
-
flush
-
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Constructor Details
-
BufferedWriteHandler
public BufferedWriteHandler()Creates a new instance with the default unboundedBlockingQueue
implementation and without buffer consolidation. -
BufferedWriteHandler
-
BufferedWriteHandler
public BufferedWriteHandler(boolean consolidateOnFlush) Creates a new instance withConcurrentLinkedQueue
- Parameters:
consolidateOnFlush
-true
if and only if the buffered write requests are merged into a single write request onflush()
-
BufferedWriteHandler
Creates a new instance with the specified thread-safe unboundedQueue
. Please note that specifying a boundedQueue
or a thread-unsafeQueue
will result in an unspecified behavior.- Parameters:
consolidateOnFlush
-true
if and only if the buffered write requests are merged into a single write request onflush()
-
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Method Details
-
isConsolidateOnFlush
public boolean isConsolidateOnFlush() -
getQueue
Returns the queue which stores the write requests. The default implementation returns the queue which was specified in the constructor. -
flush
public void flush()Sends the queued write requests to the downstream. -
flush
public void flush(boolean consolidateOnFlush) Sends the queued write requests to the downstream.- Parameters:
consolidateOnFlush
-true
if and only if the buffered write requests are merged into a single write request
-
consolidatedWrite
-
writeRequested
Stores all write requests to the queue so that they are actually written onflush()
.- Overrides:
writeRequested
in classSimpleChannelHandler
- Throws:
Exception
-
disconnectRequested
Description copied from class:SimpleChannelHandler
Invoked whenChannel.disconnect()
was called.- Overrides:
disconnectRequested
in classSimpleChannelHandler
- Throws:
Exception
-
closeRequested
Description copied from class:SimpleChannelHandler
Invoked whenChannel.close()
was called.- Overrides:
closeRequested
in classSimpleChannelHandler
- Throws:
Exception
-
channelClosed
Fail all buffered writes that are left. See <a href="https://github.com/netty/netty/issues/308>#308 for more details.- Overrides:
channelClosed
in classSimpleChannelHandler
- Throws:
Exception
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beforeAdd
- Specified by:
beforeAdd
in interfaceLifeCycleAwareChannelHandler
- Throws:
Exception
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afterAdd
- Specified by:
afterAdd
in interfaceLifeCycleAwareChannelHandler
- Throws:
Exception
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beforeRemove
- Specified by:
beforeRemove
in interfaceLifeCycleAwareChannelHandler
- Throws:
Exception
-
afterRemove
Fail all buffered writes that are left. See <a href="https://github.com/netty/netty/issues/308>#308 for more details.- Specified by:
afterRemove
in interfaceLifeCycleAwareChannelHandler
- Throws:
Exception
-