In the pthread_once(), if the initializer has already run, then the
calling thread is supposed to see accesses issued by the initializer. This means that the read of the once_control->state variable should have an acquire semantic. Use atomic_thread_fence_acq() when the value read is ONCE_DONE, instead of straightforward atomic_load_acq(), to only put a barrier when needed (*). On the other hand, the updates of the once_control->state with the intermediate progress state do not need to synchronize with other state accesses, remove _acq suffix. Reviewed by: alc (previous version) Suggested by: alc (*) Sponsored by: The FreeBSD Foundation MFC after: 1 week
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=287556
@ -68,13 +68,15 @@ _pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
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for (;;) {
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state = once_control->state;
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if (state == ONCE_DONE)
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if (state == ONCE_DONE) {
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atomic_thread_fence_acq();
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return (0);
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}
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if (state == ONCE_NEVER_DONE) {
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if (atomic_cmpset_acq_int(&once_control->state, state, ONCE_IN_PROGRESS))
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if (atomic_cmpset_int(&once_control->state, state, ONCE_IN_PROGRESS))
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break;
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} else if (state == ONCE_IN_PROGRESS) {
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if (atomic_cmpset_acq_int(&once_control->state, state, ONCE_WAIT))
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if (atomic_cmpset_int(&once_control->state, state, ONCE_WAIT))
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_thr_umtx_wait_uint(&once_control->state, ONCE_WAIT, NULL, 0);
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} else if (state == ONCE_WAIT) {
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_thr_umtx_wait_uint(&once_control->state, state, NULL, 0);
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