Drain LibMR threads to a safe point before fork() (MOD-15307)#97
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Add MR_DrainForFork()/MR_ResumeAfterFork(). On the main thread (from the module's FORK_CHILD_PRE handler) park the event-loop thread at a between-tasks safe point via a posted task and bounded-wait the worker pool to idle, so no LibMR thread holds a libc lock at fork() (ghost-lock). Bounded + fail-open; cooperative (not the SIGUSR2 mr_thpool_pause, which can freeze a worker mid-malloc). Resume releases the parked event-loop thread. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
Adds
MR_DrainForFork()/MR_ResumeAfterFork(). Called from the embedding module's pre-fork handler (main thread),MR_DrainForFork():so no LibMR thread holds a libc lock at
fork()(which would ghost-lock the child).MR_ResumeAfterFork()releases the parked event-loop thread (called after the fork, on success or cancel).Cooperative, bounded, fail-open. Deliberately not the existing
mr_thpool_pause(SIGUSR2), which can freeze a worker mid-mallocholding the arena lock — exactly the ghost-lock this prevents. A worker still blocked acquiring the GIL is already malloc-safe, so a drain timeout there is benign.Why / depends on
Fixes the RedisTimeSeries ASM-migration nightly hangs (MOD-14615 valgrind, MOD-14239 sanitizer). The embedding module wires this to redis core's new
FORK_CHILD_PREsubevent (redis/redis#15327).Pre-merge note
The two
RedisModule_Log(..., "notice", ...)lines inMR_DrainForFork/MR_ResumeAfterForkshould be downgraded todebug(kept atnoticeto confirm the drain fires during CI validation).🤖 Generated with Claude Code