Context data is lost if AsyncLogger and AsyncLoggerConfig are both used

[ppkarwasz]

Description

If the user uses both an AsyncLoggerContext (which makes all loggers to be of type AsyncLogger) and AsyncLoggerConfig, a race condition can occur, which causes context data to be lost.

Details

If both AsyncLogger and AsyncLoggerConfig are used together (which is no advised, but possible and there is a test for it):

• AsyncLoggerConfig#log is called from the main disruptor thread with a RingBufferLogEvent argument,
• AsyncLoggerConfig calls RingBufferLogEvent#createMemento() before sending the event to its own disruptor thread. However this method does not make a copy of the context data, nor does it mark the data as "frozen",
• A RingBufferLogEvent#clear() on the main disruptor thread clears the context data. If the disruptor thread of AsyncLoggerConfig didn't log the message yet, it will log it without context data.

[ppkarwasz]

This issues causes the "flakiness" AsyncLoggerThreadContextCopyOnWriteTest and related tests from #1568.

As it turns out, the tests were not "flaky", but pointed out a real problem.

[jvz]

That's the fun thing about flaky tests; sometimes they flake because they don't assert the right thing, and sometimes they flake because they don't set things up such that what they're asserting is deterministic. Nice find!