Motivation:
Calling System.nanoTime() for each channelRead(...) is very expensive. See [#3808] for more detailed description.
Also we always do extra work for each write and read even if read or write idle states should not be handled.
Modifications:
- Move System.nanoTime() call to channelReadComplete(...).
- Reuse ChannelFutureListener for writes
- Only add ChannelFutureListener to writes if write and all idle states should be handled.
- Only call System.nanoTime() for reads if idle state events for read and all states should be handled.
Result:
Less overhead when using the IdleStateHandler.
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