netty5/transport/src
Eric Anderson 6dbb610f5b Add ChannelHandlerContext.invoker()
Motivation:

Being able to access the invoker() is useful when adding additional
handlers that should be running in the same thread. Since an application
may be using a threading model unsupported by the default invoker, they
can specify their own. Because of that, in a handler that auto-adds
other handlers:

// This is a good pattern
ctx.pipeline().addBefore(ctx.invoker(), ctx.name(), null, newHandler);
// This will generally work, but prevents using custom invoker.
ctx.pipeline().addBefore(ctx.executor(), ctx.name(), null, newHandler);

That's why I believe in commit 110745b0, for the now-defunct 5.0 branch,
when ChannelHandlerAppender was added the invoker() method was also
necessary.

There is a side-benefit to exposing the invoker: in certain advanced
use-cases using the invoker for a particular handler is useful. Using
the invoker you are able to invoke a _particular_ handler, from possibly
a different thread yet still using standard exception processing.

ChannelHandlerContext does part of that, but is unwieldy when trying to
invoke a particular handler because it invokes the prev or next handler,
not the one the context is for. A workaround is to use the next or prev
context (respectively), but this breaks when the pipeline changes.

This came up during writing the Http2MultiplexCodec which uses a
separate child channel for each http/2 stream and wants to send messages
from the child channel directly to the Http2MultiplexCodec handler that
created it.

Modifications:

Add the invoker() method to ChannelHandlerContext. It was already being
implemented by AbstractChannelHandlerContext. The two other
implementations of ChannelHandlerContext needed minor tweaks.

Result:

Access to the invoker used for a particular handler, for either reusing
for other handlers or for advanced use-cases. Fixes #4738
2016-01-22 14:04:35 +01:00
..
main/java/io/netty Add ChannelHandlerContext.invoker() 2016-01-22 14:04:35 +01:00
test/java/io/netty Let CombinedChannelDuplexHandler correctly handle exceptionCaught. Related to [#4528] 2016-01-18 09:54:48 +01:00