fix(profiling): clean up containers post-fork [backport 4.5]#17726
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KowalskiThomas wants to merge 1 commit into4.5from
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fix(profiling): clean up containers post-fork [backport 4.5]#17726KowalskiThomas wants to merge 1 commit into4.5from
KowalskiThomas wants to merge 1 commit into4.5from
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Fixes a crash in the Profiler when fork is called while the Sampling Thread is actively modifying the LRUCache for Frames. Instead of calling std::list::clear() post-fork (which can crash on a corrupted list), use placement new to reinitialise the containers, abandoning the old data as an intentional one-time leak. Also adds prefork/postfork_parent handlers via pthread_atfork so that restart_after_fork uses a pre-saved flag rather than relying on thread_seq_num parity (which prefork itself changes). Backport of PR #17042 to branch 4.5.
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taegyunkim
approved these changes
May 4, 2026
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Backport of PR #17042 (commit 39a5f23) to branch 4.5.
Description
Fixes a crash in the Profiler (~100/week) when
forkis called while the Sampling Thread is actively modifying theLRUCachefor Frames.The root cause:
postfork_childcalledframe_cache_.clear(), which traverses thestd::listto free nodes. If the sampling thread was mid-operation (splice inlookup,emplace_front/pop_backinstore) at fork time, the list's internal pointers can be in a corrupted state in the child, causing the crash.Fix: replace
clear()withpostfork_child()which uses placement new to construct fresh empty containers, abandoning the old data as an intentional one-time leak.Also adds
prefork()/postfork_parent()atfork handlers registered viapthread_atforkso thatrestart_after_forkuses a pre-savedwas_running_at_fork_flag instead of relying onthread_seq_numparity (whichpreforkitself changes).Notes on conflict resolution
The 4.5 branch uses a
_stack_function-name prefix (with leading underscore) for its internal atfork helpers, unlikemain/4.6/4.7 which usestack_. The new_stack_atfork_prepareand_stack_atfork_parentfunctions follow the same_stack_convention.