Motivation:
When always triggered fireChannelWritabilityChanged() directly when the update the pending bytes in the ChannelOutboundBuffer was made from within the EventLoop. This is problematic as this can cause some re-entrance issue if the user has a custom ChannelOutboundHandler that does multiple writes from within the write(...) method and also has a handler that will intercept the channelWritabilityChanged event and trigger another write when the Channel is writable. This can also easily happen if the user just use a MessageToMessageEncoder subclass and triggers a write from channelWritabilityChanged().
Beside this we also triggered fireChannelWritabilityChanged() too often when a user did a write from outside the EventLoop. In this case we increased the pending bytes of the outboundbuffer before scheduled the actual write and decreased again before the write then takes place. Both of this may trigger a fireChannelWritabilityChanged() event which then may be re-triggered once the actual write ends again in the ChannelOutboundBuffer.
The third gotcha was that a user may get multiple events even if the writability of the channel not changed.
Modification:
- Always invoke the fireChannelWritabilityChanged() later on the EventLoop.
- Only trigger the fireChannelWritabilityChanged() if the channel is still active and if the writability of the channel changed. No need to cause events that were already triggered without a real writability change.
- when write(...) is called from outside the EventLoop we only increase the pending bytes in the outbound buffer (so that Channel.isWritable() is updated directly) but not cause a fireChannelWritabilityChanged(). The fireChannelWritabilityChanged() is then triggered once the task is picked up by the EventLoop as usual.
Result:
No more re-entrance possible because of writes from within channelWritabilityChanged(...) method and no events without a real writability change.
Motivation:
When a promise is notified that was already added to the ChannelOutboundBuffer and we try to notify it later on we only see a warning that it was notified before. This is often not very useful as we have no idea where it was notified at all. We can do better in case it was failed before (which is most of the times the case) and just also log the cause that was used for it.
Modifications:
Add the cause that was used to notify the promise when we fail to notify it as part of the ChannelOutboundBuffer.
Result:
Easier to debug user errors.
Motivation:
If a handler is added to the pipeline within ChannelInitializer::initChannel via
addFirst(...) then it will not receive the channelRegistered event. The same
handler added via addLast(...) will receive the event. This different behavior
is unlikely to be expected by users and can cause confusion.
Modifications:
Let ChannelInitializer::channelRegistered propagate the event by passing it to
the pipeline instead of firing it on the ChannelHandlerContext.
Result:
The channelRegistered event is propagated to handlers regardless of the method
used to add it to the pipeline (addFirst/addLast).
Motivation:
NIO now supports a pluggable select strategy, but EPOLL currently doesn't support this. We should strive for feature parity for EPOLL.
Modifications:
- Add SelectStrategy to EPOLL transport.
Result:
EPOLL transport supports SelectStategy.
Motivation:
Under high throughput/low latency workloads, selector wakeups are
degrading performance when the incoming operations are triggered
from outside of the event loop. This is a common scenario for
"client" applications where the originating input is coming from
application threads rather from the socket attached inside the
event loops.
As a result, it can be desirable to defer the blocking select
so that incoming tasks (write/flush) do not need to wakeup
the selector.
Modifications:
This changeset adds the notion of a generic SelectStrategy which,
based on its contract, allows the implementation to optionally
defer the blocking select based on some custom criteria.
The default implementation resembles the original behaviour, that
is if tasks are in the queue `selectNow()` and move on, and if no
tasks need to be processed go into the blocking select and wait
for wakeup.
The strategy can be customized per `NioEventLoopGroup` in the
constructor.
Result:
High performance client applications are now given the chance to
customize for how long the actual selector blocking should be
deferred by employing a custom select strategy.
Motivation:
We need to ensure we run all pending tasks before doing any flush in writeOutbound(...) to ensure all pending tasks are run first. Also we should remove the assert of the future and just add a listener to it so it is processed later if needed. This is true as a user may schedule a write for later execution.
Modifications:
- Remove assert of future in writeOutbound(...)
- Correctly run pending tasks before doing the flush and also before doing the close of the channel.
- Add unit tests to proof the defect is fixed.
Result:
Correclty handle the situation of delayed writes.
Motivation:
Often the user uses EmbeddedChannel within unit tests where the only "important" thing is to know if any pending messages were in the buffer and then release these.
We should provide methods for this so the user not need to manually loop through these and release.
Modifications:
Add methods to easily handle releasing of messages.
Result:
Less boiler-plate code for the user to write.
Motivation:
PromiseAggregator's API allows for the aggregate promise to complete before the user is done adding promises. In order to support this use case the API structure would need to change in a breaking manner.
Modifications:
- Deprecate PromiseAggregator and subclasses
- Introduce PromiseCombiner which corrects these issues
Result:
PromiseCombiner corrects the deficiencies in PromiseAggregator.
Motivation:
PendingWriteQueue should guard against re-entrant writes once
removeAndFailAll() is run.
Modifications:
removeAndFailAll() should repeat until the queue is finally empty.
Result:
assertEmpty() will always hold.
Motivation:
We should guard users from using Unsafe methods from outside the EventLoop if not designed to do so.
Modifications:
Add asserts
Result:
Easier for users to detect miss-use.
Motivation:
DefaultChannelHandlerContext calls a utility method validatePromise which may throw if the arguments are not valid. If this method throws then the message will not be released.
Modifications:
- If an exception is thrown the message should be released
Result:
No more leak in DefaultChannelHandlerContext.write
Motivation:
See #3746.
Modifications:
Fork SpscLinkedQueue and SpscLinkedAtomicQueue from JCTools based on 7846450e28
Result:
Add SpscLinkedQueue and SpscLinkedAtomicQueue and apply it in LocalChannel.
Motivation:
See #4882
Modification:
isInputShutdown, isOutputShutdown and shutdownOutput methods moved from io.netty.channel.socket.SocketChannel to a new interface io.netty.channel.socket.DuplexChannel.
io.netty.channel.unix.DomainSocketChannel now extends DuplexChannel
Methods implementing DuplexChannel moved from EpollSocketChannel to AbstractEpollStreamChannel.
Result:
Possible to call shutdownOutput on EpollDomainSocketChannel
Motiviation:
We should ensure that handlerAdded(...) and handlerRemoved(...) is always called from the EventExecutor that also invokes the other methods of the ChannelHandler. Also we need to ensure we always call handlerAdded(...) before any other method can be calld to ensure correct ordering.
Motifications:
- Ensure that the right thread is used to call the methods
- Ensure correct ordering
- Add tests
Result:
Respect the thread-model for handlerAdded(...) and handlerRemoved(...) and preserve correct ordering in all cases.
Motivation:
When a channel was registered before and is re-registered we need to respect ChannelConfig.isAutoRead() and so start reading one the registration task completes. This was done "by luck" before 15162202fb.
Modifications:
Explicit start reading once a Channel was re-registered if isAutoRead() is true.
Result:
Correctly receive data after re-registration completes.
Motivation:
Due a regression introduced by e969b6917c we missed to pass the original ChannelPromise to the next ChannelOutboundHandler and so
may never notify the origin ChannelPromise. This is related to #4805.
Modifications:
- Correctly pass the ChannelPromise
- Add unit test.
Result:
Correctly pass the ChannelPromise on deregister(...)
Motivation:
fix the issue netty#2944
Modifications:
(1) use - instead of =>, use ! instead of :> due to the connection is bidirectional. What's more, toString() method don't know the direction or there is no need to know the direction when only log channel information.
(2) add L： before local address and R: before remote address.
Result:
after the fix, toString() won't confuse the user.
Motivation:
If a user adds a ChannelHandler from outside the EventLoop it is possible to get into the situation that handlerAdded(...) is scheduled on the EventLoop and so called after another methods of the ChannelHandler as the EventLoop may already be executing on this point in time.
Modification:
- Ensure we always check if the handlerAdded(...) method was called already and if not add the currently needed call to the EventLoop so it will be picked up after handlerAdded(...) was called. This works as if the handler is added to the ChannelPipeline from outside the EventLoop the actual handlerAdded(...) operation is scheduled on the EventLoop.
- Some cleanup in the DefaultChannelPipeline
Result:
Correctly order of method executions of ChannelHandler.
Motivation:
ChannelOutboundHandlerAdapter's javadoc has some minor issues.
Modifications:
Fix the minor javadoc issues and resolves#4752.
Result:
ChannelOutboundHandlerAdapter's javadoc issues are fixed.
Motivation:
ChannelInboundHandler and ChannelOutboundHandler both can implement exceptionCaught(...) method and so we need to dispatch to both of them.
Modifications:
- Correctly first dispatch exceptionCaught to the ChannelInboundHandler but also make sure the next handler it will be dispatched to will be the ChannelOutboundHandler
- Add removeInboundHandler() and removeOutboundHandler() which allows to remove one of the combined handlers
Result:
Correctly handle events
Motivation:
Our contract in Channels is that the promise should always be notified before the actual callbacks of the ChannelInboundHandler are called. This was not done in the LocalChannel and so the behavior was different to other Channel implementations.
Modifications:
- First complete the ChannelPromise then call fireChannelActive()
- Guard against NPE when doClose() was called before the task was executed.
Result:
Consistent behavior between LocalChannel and other Channel implementations.
Motivation:
In AbstractChannelTest we not correctly mocked some methods which could lead to test errors. That said it only showed up here when running from the IDE and not from the cmdLine.
Modifications:
Mock methods that are needed for the test
Result:
Test pass in the IDE as well.
Motivation:
At the moment EmbeddedChannel always handle close() and disconnect() the same way which also means that ChannelOutboundHandler.disconnect(...) will never called. We should allow to specify if these are handle different or not to make the use of EmbeddedChannel more flexible.
Modifications:
Add 2 other constructors which allow to specify if disconnect / close are handled the same way or differently.
Result:
More flexible usage of EmbeddedChannel possible.
Motivation:
The prefix fix of #2363 did not correctly handle the case when selectAgain is true and so missed to null out entries.
Modifications:
Move the i++ from end of loop to beginning of loop
Result:
Entries in the array will be null out so allow to have these GC'ed once the Channel close
Motivation:
We often used synchronized(this) while the whole method was synchronized, which can be simplified by just mark the whole method as synchronized.
Modifications:
Replace synchronized(this) with synchronized on the method
Result:
Cleaner code
Motivation:
As a user may call deregister() from within any method while doing processing in the ChannelPipeline, we need to ensure we do the actual deregister operation later. This is needed as for example, we may be in the ByteToMessageDecoder.callDecode(...) method and so still try to do processing in the old EventLoop while the user already registered the Channel to a new EventLoop. Without delay, the deregister operation this could lead to have a handler invoked by different EventLoop and so threads.
Modifications:
Ensure the actual deregister will be done later on and not directly when invoked.
Result:
Calling deregister() within ByteToMessageDecoder.decode(..) is safe.
Motivation:
Estimation algorithm currently used for WriteTasks is complicated and
wrong. Additionally, some code relies on outbound buffer size
incremented only on actual writes to the outbound buffer.
Modifications:
- Throw away the old estimator and replace with a simple algorithm that
uses the client-provided estimator along with a statically configured
WriteTask overhead (io.netty.transport.writeTaskSizeOverhead system
property with the default value of 48 bytes)
- Add a io.netty.transport.estimateSizeOnSubmit boolean system property
allowing the clients to disable the message estimation outside the
event loop
Result:
Task estimation is user controllable and produces better results by
default
Motivation:
We need to remove all registered events for a Channel from the EventLoop before doing the actual close to ensure we not produce a cpu spin when the actual close operation is delayed or executed outside of the EventLoop.
Modifications:
Deregister for events for NIO and EPOLL socket implementations when SO_LINGER is used.
Result:
No more cpu spin.
Motivation:
Fix a race-condition when closing NioSocketChannel or EpollSocketChannel while try to detect if a close executor should be used and the underlying socket was already closed. This could lead to an exception that then leave the channel / in an invalid state and so could lead to side-effects like heavy CPU usage.
Modifications:
Catch possible socket exception while try to get the SO_LINGER options from the underlying socket.
Result:
No more race-condition when closing the channel is possible with bad side-effects.
Motivation:
The javadocs for ChannelOption.AUTO_CLOSE say the default is false, but the default is currently true.
Modifications:
- Make javadocs consistent with code
Result:
Less confusing docs.
Motivation:
exceptionCaught(...) will only handle inbound exceptions which means it makes not much sense to have it also on ChannelOutboundHandler. Because of this we should move it to ChannelInboundHandler.
Modifications:
Add @deprecated annotation to ChannelHandler.exceptionCaught(...).
Result:
Preapre to cleanup the API in later release.
Motivation:
We should use OneTimeTask where possible to reduce object creation.
Modifications:
Replace Runnable with OneTimeTask
Result:
Less object creation
Motivation:
If you need to handle a lot of concurrent connections (1M+) the memory footprint can be problem.
Modifications:
- Lazy create the IdentityHashMap that holds the EventExecutor mappings as this is not needed by most users anyway
- Use a sane initial capacity when creating the IdentityHashMap
Result:
Smaller memory footprint of DefaultChannelPipeline
Motivation:
We not need to store another reference to AbstractChannel as we can access it through DefaultChannelHandlerContext.
Modifications:
Remove reference.
Result:
Cleaner code.
Motivation:
If you start to have 1M+ concurrent connections memory footprint can be come a big issue. We should try to reduce it as much as possible in the core of netty.
Modifications:
- Remove HashMap that was used to store name to ctx mapping. This was only used for validation and access a handler by name. As a pipeline is not expected to be very long (like 100+ handlers) we can just walk the linked list structure to find the ctx with a given name.
Result:
Less memory footprint of the DefaultChannelPipeline.
