Appender: Use channel to signal shutdown of worker thread #701
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Motivation
Fixes a race condition which occurs on dropping of
WorkerGuard
. If the worker thread missed seeing the shutdown signal in time, it would end up blocking on trying to callrecv()
on the crossbeam channel and block indefinitely.This bug was identified in #678
Solution
Signal that the worker should stop by sending a
ShutDown
message through the crossbeam channel.