Capture the MDC and thread name before queueing the event - #32
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…nder thread Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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Reported in #23.
append()queues theILoggingEventas is and everything is read from it later, on the sender thread. Logback fills the MDC map and the thread name of aLoggingEventlazily, from whichever thread first asks for them, so by the timebuildPostData()runs, the logging thread's MDC is gone:metanever carries the configuredmdcFieldsunless the flush happens to run on the logging thread itself (which is why the integration tests, which callflush()synchronously, never noticed), andruntime.threadreports the sender thread instead of the thread that logged.The fix is what logback's own
AsyncAppenderdoes before handing an event to another thread:append()now callsevent.prepareForDeferredProcessing(), which captures the formatted message, the thread name and the MDC map while the event is still on the logging thread. Caller data is deliberately not captured here, since computing it walks the stack on every log call and logback keeps that opt-in for the same reason.The first commit is the failing test on its own and is expected to fail CI; the second commit makes it pass.
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