The FlowControlHandler ensures that only one message per read() is sent downstream. Classes such as ByteToMessageDecoder or MessageToByteEncoder are free to emit as many events as they like for any given input. A channel's auto reading configuration doesn't usually apply in these scenarios. This is causing problems in downstream ChannelHandlers that would like to hold subsequent events while they're processing one event. It's a common problem with the HttpObjectDecoder that will very often fire an HttpRequest that is immediately followed by a LastHttpContent event.

ChannelPipeline pipeline = ...;

pipeline.addLast(new HttpServerCodec());
pipeline.addLast(new FlowControlHandler());

pipeline.addLast(new MyExampleHandler());

class MyExampleHandler extends ChannelInboundHandlerAdapter {
  @Override
  public void channelRead(ChannelHandlerContext ctx, Object msg) {
    if (msg instanceof HttpRequest) {
      ctx.channel().config().setAutoRead(false);

      // The FlowControlHandler will hold any subsequent events that
      // were emitted by HttpObjectDecoder until auto reading is turned
      // back on or Channel#read() is being called.
    }
  }
}

Nested and Inner Type Summary

Modifier and Type	Class and Description
private static class	FlowControlHandler.RecyclableArrayDeque A recyclable `ArrayDeque`.

Field Summary

Modifier and Type	Field and Description
private ChannelConfig	config
private static final InternalLogger	logger
private FlowControlHandler.RecyclableArrayDeque	queue
private final boolean	releaseMessages
private boolean	shouldConsume

Constructor Summary

Access	Constructor and Description
public	FlowControlHandler()
public	FlowControlHandler(boolean releaseMessages)

Method Summary

Modifier and Type	Method and Description
public void	channelInactive(ChannelHandlerContext ctx) Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelInactive. Implements io.netty.channel.ChannelInboundHandler.channelInactive. Calls `ChannelHandlerContext#fireChannelInactive()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
public void	channelRead(ChannelHandlerContext ctx, Object msg) Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelRead. Implements io.netty.channel.ChannelInboundHandler.channelRead. Calls `ChannelHandlerContext#fireChannelRead(Object)` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
public void	channelReadComplete(ChannelHandlerContext ctx) Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelReadComplete. Implements io.netty.channel.ChannelInboundHandler.channelReadComplete. Calls `ChannelHandlerContext#fireChannelReadComplete()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`.
private int	dequeue(ChannelHandlerContext ctx, int minConsume) Dequeues one or many (or none) messages depending on the channel's auto reading state and returns the number of messages that were consumed from the internal queue.
private void	destroy() Releases all messages and destroys the `Queue`.
public void	handlerAdded(ChannelHandlerContext ctx) Overrides io.netty.channel.ChannelHandlerAdapter.handlerAdded. Implements io.netty.channel.ChannelHandler.handlerAdded. Gets called after the `ChannelHandler` was added to the actual context and it's ready to handle events.
public void	handlerRemoved(ChannelHandlerContext ctx) Overrides io.netty.channel.ChannelHandlerAdapter.handlerRemoved. Implements io.netty.channel.ChannelHandler.handlerRemoved. Gets called after the `ChannelHandler` was removed from the actual context and it doesn't handle events anymore.
pack-priv boolean	isQueueEmpty() Determine if the underlying `Queue` is empty.
public void	read(ChannelHandlerContext ctx) Overrides io.netty.channel.ChannelDuplexHandler.read. Implements io.netty.channel.ChannelOutboundHandler.read. Calls `ChannelHandlerContext#read()` to forward to the next `ChannelOutboundHandler` in the `ChannelPipeline`.

Inherited from io.netty.channel.ChannelDuplexHandler:: bind close connect deregister disconnect flush write

Field Detail

config	back to summary
private ChannelConfig config

logger	back to summary
private static final InternalLogger logger

queue	back to summary
private FlowControlHandler.RecyclableArrayDeque queue

releaseMessages	back to summary
private final boolean releaseMessages

shouldConsume	back to summary
private boolean shouldConsume

Constructor Detail

FlowControlHandler	back to summary
public FlowControlHandler()

FlowControlHandler	back to summary
public FlowControlHandler(boolean releaseMessages)

Method Detail

channelInactive back to summary

channelInactive	back to summary
public void channelInactive(ChannelHandlerContext ctx) throws Exception Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelInactive. Implements io.netty.channel.ChannelInboundHandler.channelInactive. Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelInactive. Calls `ChannelHandlerContext#fireChannelInactive()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`. Sub-classes may override this method to change behavior. Annotations @Override

public void channelInactive(ChannelHandlerContext ctx) throws Exception

Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelInactive.

Implements io.netty.channel.ChannelInboundHandler.channelInactive.

Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelInactive.

Calls ChannelHandlerContext#fireChannelInactive() to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.

Annotations

@Override

channelRead back to summary

channelRead	back to summary
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelRead. Implements io.netty.channel.ChannelInboundHandler.channelRead. Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelRead. Calls `ChannelHandlerContext#fireChannelRead(Object)` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`. Sub-classes may override this method to change behavior. Annotations @Override

public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception

Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelRead.

Implements io.netty.channel.ChannelInboundHandler.channelRead.

Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelRead.

Calls ChannelHandlerContext#fireChannelRead(Object) to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.

Annotations

@Override

channelReadComplete back to summary

channelReadComplete	back to summary
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelReadComplete. Implements io.netty.channel.ChannelInboundHandler.channelReadComplete. Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelReadComplete. Calls `ChannelHandlerContext#fireChannelReadComplete()` to forward to the next `ChannelInboundHandler` in the `ChannelPipeline`. Sub-classes may override this method to change behavior. Annotations @Override

public void channelReadComplete(ChannelHandlerContext ctx) throws Exception

Overrides io.netty.channel.ChannelInboundHandlerAdapter.channelReadComplete.

Implements io.netty.channel.ChannelInboundHandler.channelReadComplete.

Doc from io.netty.channel.ChannelInboundHandlerAdapter.channelReadComplete.

Calls ChannelHandlerContext#fireChannelReadComplete() to forward to the next ChannelInboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.

Annotations

@Override

dequeue back to summary

dequeue	back to summary
private int dequeue(ChannelHandlerContext ctx, int minConsume) Dequeues one or many (or none) messages depending on the channel's auto reading state and returns the number of messages that were consumed from the internal queue. The `minConsume` argument is used to force `dequeue()` into consuming that number of messages regardless of the channel's auto reading configuration. See Also `read(ChannelHandlerContext)`, `channelRead(ChannelHandlerContext, Object)`

private int dequeue(ChannelHandlerContext ctx, int minConsume)

Dequeues one or many (or none) messages depending on the channel's auto reading state and returns the number of messages that were consumed from the internal queue. The minConsume argument is used to force dequeue() into consuming that number of messages regardless of the channel's auto reading configuration.

See Also: read(ChannelHandlerContext), channelRead(ChannelHandlerContext, Object)

destroy	back to summary
private void destroy() Releases all messages and destroys the `Queue`.

handlerAdded back to summary

handlerAdded	back to summary
public void handlerAdded(ChannelHandlerContext ctx) throws Exception Overrides io.netty.channel.ChannelHandlerAdapter.handlerAdded. Implements io.netty.channel.ChannelHandler.handlerAdded. Doc from io.netty.channel.ChannelHandler.handlerAdded. Gets called after the `ChannelHandler` was added to the actual context and it's ready to handle events. Annotations @Override

public void handlerAdded(ChannelHandlerContext ctx) throws Exception

Overrides io.netty.channel.ChannelHandlerAdapter.handlerAdded.

Implements io.netty.channel.ChannelHandler.handlerAdded.

Doc from io.netty.channel.ChannelHandler.handlerAdded.

Gets called after the ChannelHandler was added to the actual context and it's ready to handle events.

Annotations

@Override

handlerRemoved back to summary

handlerRemoved	back to summary
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception Overrides io.netty.channel.ChannelHandlerAdapter.handlerRemoved. Implements io.netty.channel.ChannelHandler.handlerRemoved. Doc from io.netty.channel.ChannelHandler.handlerRemoved. Gets called after the `ChannelHandler` was removed from the actual context and it doesn't handle events anymore. Annotations @Override

public void handlerRemoved(ChannelHandlerContext ctx) throws Exception

Overrides io.netty.channel.ChannelHandlerAdapter.handlerRemoved.

Implements io.netty.channel.ChannelHandler.handlerRemoved.

Doc from io.netty.channel.ChannelHandler.handlerRemoved.

Gets called after the ChannelHandler was removed from the actual context and it doesn't handle events anymore.

Annotations

@Override

isQueueEmpty	back to summary
pack-priv boolean isQueueEmpty() Determine if the underlying `Queue` is empty. This method exists for testing, debugging and inspection purposes and it is not Thread safe!

read back to summary

read	back to summary
public void read(ChannelHandlerContext ctx) throws Exception Overrides io.netty.channel.ChannelDuplexHandler.read. Implements io.netty.channel.ChannelOutboundHandler.read. Doc from io.netty.channel.ChannelDuplexHandler.read. Calls `ChannelHandlerContext#read()` to forward to the next `ChannelOutboundHandler` in the `ChannelPipeline`. Sub-classes may override this method to change behavior. Annotations @Override

public void read(ChannelHandlerContext ctx) throws Exception

Overrides io.netty.channel.ChannelDuplexHandler.read.

Implements io.netty.channel.ChannelOutboundHandler.read.

Doc from io.netty.channel.ChannelDuplexHandler.read.

Calls ChannelHandlerContext#read() to forward to the next ChannelOutboundHandler in the ChannelPipeline. Sub-classes may override this method to change behavior.

Annotations

@Override

io.netty.handler.flow back to summary

private final Class FlowControlHandler.RecyclableArrayDeque

Class Inheritance

extends ArrayDeque<Object>

java.lang.Object
java.util.AbstractCollection
java.util.ArrayDeque
io.netty.handler.flow.FlowControlHandler.RecyclableArrayDeque

A recyclable ArrayDeque.

Field Summary

Modifier and Type	Field and Description
private static final int	DEFAULT_NUM_ELEMENTS A value of `2` should be a good choice for most scenarios.
private final ObjectPool.Handle<FlowControlHandler.RecyclableArrayDeque>	handle
private static final ObjectPool<FlowControlHandler.RecyclableArrayDeque>	RECYCLER
private static final long	serialVersionUID Hides java.util.ArrayDeque.serialVersionUID.

Constructor Summary

Access	Constructor and Description
private	RecyclableArrayDeque(int numElements, ObjectPool.Handle<FlowControlHandler.RecyclableArrayDeque> handle)

Method Summary

Modifier and Type	Method and Description
public static FlowControlHandler.RecyclableArrayDeque	newInstance()
public void	recycle()

Field Detail

DEFAULT_NUM_ELEMENTS	back to summary
private static final int DEFAULT_NUM_ELEMENTS A value of `2` should be a good choice for most scenarios.

handle	back to summary
private final ObjectPool.Handle<FlowControlHandler.RecyclableArrayDeque> handle

RECYCLER	back to summary
private static final ObjectPool<FlowControlHandler.RecyclableArrayDeque> RECYCLER

serialVersionUID	back to summary
private static final long serialVersionUID Hides java.util.ArrayDeque.serialVersionUID.

Constructor Detail

RecyclableArrayDeque	back to summary
private RecyclableArrayDeque(int numElements, ObjectPool.Handle<FlowControlHandler.RecyclableArrayDeque> handle)

Method Detail

newInstance	back to summary
public static FlowControlHandler.RecyclableArrayDeque newInstance()

recycle	back to summary
public void recycle()

public Class FlowControlHandler

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private final Class FlowControlHandler.RecyclableArrayDeque

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail