Motivation:
ChannelHandlerContext, ChannelPipeline and Channel share various method signatures. We should provide an interface to share.
Modifications:
Add ChannelInboundInvoker and ChannelOutboundInvoker and extend these.
Result:
Better API abstraction.
- write() now accepts a ChannelPromise and returns ChannelFuture as most
users expected. It makes the user's life much easier because it is
now much easier to get notified when a specific message has been
written.
- flush() does not create a ChannelPromise nor returns ChannelFuture.
It is now similar to what read() looks like.
- Remove channelReadSuspended because it's actually same with messageReceivedLast
- Rename messageReceived to channelRead
- Rename messageReceivedLast to channelReadComplete
We renamed messageReceivedLast to channelReadComplete because it
reflects what it really is for. Also, we renamed messageReceived to
channelRead for consistency in method names.
I must admit MesageList was pain in the ass. Instead of forcing a
handler always loop over the list of messages, this commit splits
messageReceived(ctx, list) into two event handlers:
- messageReceived(ctx, msg)
- mmessageReceivedLast(ctx)
When Netty reads one or more messages, messageReceived(ctx, msg) event
is triggered for each message. Once the current read operation is
finished, messageReceivedLast() is triggered to tell the handler that
the last messageReceived() was the last message in the current batch.
Similarly, for outbound, write(ctx, list) has been split into two:
- write(ctx, msg)
- flush(ctx, promise)
Instead of writing a list of message with a promise, a user is now
supposed to call write(msg) multiple times and then call flush() to
actually flush the buffered messages.
Please note that write() doesn't have a promise with it. You must call
flush() to get notified on completion. (or you can use writeAndFlush())
Other changes:
- Because MessageList is completely hidden, codec framework uses
List<Object> instead of MessageList as an output parameter.
The API changes made so far turned out to increase the memory footprint
and consumption while our intention was actually decreasing them.
Memory consumption issue:
When there are many connections which does not exchange data frequently,
the old Netty 4 API spent a lot more memory than 3 because it always
allocates per-handler buffer for each connection unless otherwise
explicitly stated by a user. In a usual real world load, a client
doesn't always send requests without pausing, so the idea of having a
buffer whose life cycle if bound to the life cycle of a connection
didn't work as expected.
Memory footprint issue:
The old Netty 4 API decreased overall memory footprint by a great deal
in many cases. It was mainly because the old Netty 4 API did not
allocate a new buffer and event object for each read. Instead, it
created a new buffer for each handler in a pipeline. This works pretty
well as long as the number of handlers in a pipeline is only a few.
However, for a highly modular application with many handlers which
handles connections which lasts for relatively short period, it actually
makes the memory footprint issue much worse.
Changes:
All in all, this is about retaining all the good changes we made in 4 so
far such as better thread model and going back to the way how we dealt
with message events in 3.
To fix the memory consumption/footprint issue mentioned above, we made a
hard decision to break the backward compatibility again with the
following changes:
- Remove MessageBuf
- Merge Buf into ByteBuf
- Merge ChannelInboundByte/MessageHandler and ChannelStateHandler into ChannelInboundHandler
- Similar changes were made to the adapter classes
- Merge ChannelOutboundByte/MessageHandler and ChannelOperationHandler into ChannelOutboundHandler
- Similar changes were made to the adapter classes
- Introduce MessageList which is similar to `MessageEvent` in Netty 3
- Replace inboundBufferUpdated(ctx) with messageReceived(ctx, MessageList)
- Replace flush(ctx, promise) with write(ctx, MessageList, promise)
- Remove ByteToByteEncoder/Decoder/Codec
- Replaced by MessageToByteEncoder<ByteBuf>, ByteToMessageDecoder<ByteBuf>, and ByteMessageCodec<ByteBuf>
- Merge EmbeddedByteChannel and EmbeddedMessageChannel into EmbeddedChannel
- Add SimpleChannelInboundHandler which is sometimes more useful than
ChannelInboundHandlerAdapter
- Bring back Channel.isWritable() from Netty 3
- Add ChannelInboundHandler.channelWritabilityChanges() event
- Add RecvByteBufAllocator configuration property
- Similar to ReceiveBufferSizePredictor in Netty 3
- Some existing configuration properties such as
DatagramChannelConfig.receivePacketSize is gone now.
- Remove suspend/resumeIntermediaryDeallocation() in ByteBuf
This change would have been impossible without @normanmaurer's help. He
fixed, ported, and improved many parts of the changes.
- Rename ChannelHandlerAdapter to ChannelDuplexHandler
- Add ChannelHandlerAdapter that implements only ChannelHandler
- Rename CombinedChannelHandler to CombinedChannelDuplexHandler and
improve runtime validation
- Remove ChannelInbound/OutboundHandlerAdapter which are not useful
- Make ChannelOutboundByteHandlerAdapter similar to
ChannelInboundByteHandlerAdapter
- Make the tail and head handler of DefaultChannelPipeline accept both
bytes and messages. ChannelHandlerContext.hasNext*() were removed
because they always return true now.
- Removed various unnecessary null checks.
- Correct method/field names:
inboundBufferSuspended -> channelReadSuspended
This pull request adds two new handler methods: discardInboundReadBytes(ctx) and discardOutboundReadBytes(ctx) to ChannelInboundByteHandler and ChannelOutboundByteHandler respectively. They are called between every inboundBufferUpdated() and flush() respectively. Their default implementation is to call discardSomeReadBytes() on their buffers and a user can override this behavior easily. For example, ReplayingDecoder.discardInboundReadBytes() looks like the following:
@Override
public void discardInboundReadBytes(ChannelHandlerContext ctx) throws Exception {
ByteBuf in = ctx.inboundByteBuffer();
final int oldReaderIndex = in.readerIndex();
super.discardInboundReadBytes(ctx);
final int newReaderIndex = in.readerIndex();
checkpoint -= oldReaderIndex - newReaderIndex;
}
If a handler, which has its own buffer index variable, extends ReplayingDecoder or ByteToMessageDecoder, the handler can also override discardInboundReadBytes() and adjust its index variable accordingly.
This pull request introduces a new operation called read() that replaces the existing inbound traffic control method. EventLoop now performs socket reads only when the read() operation has been issued. Once the requested read() operation is actually performed, EventLoop triggers an inboundBufferSuspended event that tells the handlers that the requested read() operation has been performed and the inbound traffic has been suspended again. A handler can decide to continue reading or not.
Unlike other outbound operations, read() does not use ChannelFuture at all to avoid GC cost. If there's a good reason to create a new future per read at the GC cost, I'll change this.
This pull request consequently removes the readable property in ChannelHandlerContext, which means how the traffic control works changed significantly.
This pull request also adds a new configuration property ChannelOption.AUTO_READ whose default value is true. If true, Netty will call ctx.read() for you. If you need a close control over when read() is called, you can set it to false.
Another interesting fact is that non-terminal handlers do not really need to call read() at all. Only the last inbound handler will have to call it, and that's just enough. Actually, you don't even need to call it at the last handler in most cases because of the ChannelOption.AUTO_READ mentioned above.
There's no serious backward compatibility issue. If the compiler complains your handler does not implement the read() method, add the following:
public void read(ChannelHandlerContext ctx) throws Exception {
ctx.read();
}
Note that this pull request certainly makes bounded inbound buffer support very easy, but itself does not add the bounded inbound buffer support.
- Previous API did not support the pipeline which contains multiple
MessageToStreamEncoders because there was no way to find the closest
outbound byte buffer. Now you always get the correct buffer even if
the handler that provides the buffer is placed distantly.
For example:
Channel -> MsgAEncoder -> MsgBEncoder -> MsgCEncoder
Msg(A|B|C)Encoder will all have access to the channel's outbound
byte buffer. Previously, it was simply impossible.
- Improved ChannelBufferHolder.toString()
- Optimized AbstractChannelBuffer.discardReadBytes()
- Split ChannelHandlerInvoker into ChannelInboundInvoker and
ChannelOutboundInvoker
- Channel implements ChannelOutboundInvoker
- ChannelOutboundInvoker.nextOut() is now out()
- ChannelOutboundHandlerContext.out() is now prevOut()
- Added the outbound operations without future
parameter to ChannelOutboundInvoker for user convenience
- All async operations which requires a ChannelFuture as a parameter
now returns ChannelFuture for user convenience
- Added ChannelFutureFactory.newVoidFuture() to allow a user specify
a dummy future that is of no use
- I'm unsure if it is actually a good idea to introduce it. It might
go away later.
- Made the contract of AbstractChannel.doXXX() much simpler and moved
all common code up to AbstractChannel.DefaultUnsafe
- Added Channel.isOpen()
- Fixed a bug where MultithreadEventLoop always shut down its child
event loops on construction
- Maybe more changes I don't remember :-)
