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fix(when_any): guard stop callback against inline completion destroying the opstate - #2115
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…ng the opstate If every child completes set_stopped() synchronously from inside __stop_source_.request_stop() (senders that complete inline from their stop callbacks), __count_ reaches zero and the receiver is completed -- destroying the operation state, including __stop_source_, while request_stop() is still iterating its callback list. The subsequent relock then spins on freed memory. Adopt __when_all's rug-pull guard: temporarily increment __count_ around request_stop() in the stop callback and arrive afterwards, so completion is deferred until the callback has returned.
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The stop callbacks that when_all (since NVIDIA#1718) and exec::when_any (since NVIDIA#2115) register on the receiver's stop token increment the count of outstanding children, request stop, and then arrive. If the last child arrives on another thread while such a callback is running, the count is already zero, so the callback's arrival completes the operation a second time. With inplace_stop_source the thread of the last child usually spins forever in ~inplace_stop_callback instead, waiting for a callback that the other thread has already destroyed. The extra count only worked around inplace_stop_source not tolerating its destruction from inside its own request_stop() (NVIDIA#1889), which NVIDIA#2303 fixed. Make both callbacks only forward the request to the internal stop source, like on-stop-request in [exec.when.all]. For when_all this also undoes the rest of the workaround from NVIDIA#1851: it completes with set_stopped only when a child does, and it no longer records values once a child has failed or been stopped. Co-Authored-By: Claude Opus 5.5 <[email protected]>
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If every child completes
set_stopped()synchronously from inside__stop_source_.request_stop()(senders that complete inline from their stop callbacks),__count_reaches zero and the receiver is completed -destroying the operation state, including__stop_source_, whilerequest_stop()is still iterating its callback list. The subsequent relock then spins on freed memory.Adopt
__when_all's rug-pull guard: temporarily increment__count_aroundrequest_stop()in the stop callback and arrive afterwards, so completion is deferred until the callback has returned.https://godbolt.org/z/sPWeEEesE