https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106183
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:ed58809ea1a8ccc1829d830799d34aa51e51d39e commit r11-10472-ged58809ea1a8ccc1829d830799d34aa51e51d39e Author: Jonathan Wakely <jwak...@redhat.com> Date: Thu Jul 28 16:15:58 2022 +0100 libstdc++: Unblock atomic wait on non-futex platforms [PR106183] When using a mutex and condition variable, the notifying thread needs to increment _M_ver while holding the mutex lock, and the waiting thread needs to re-check after locking the mutex. This avoids a missed notification as described in the PR. By moving the increment of _M_ver to the base _M_notify we can make the use of the mutex local to the use of the condition variable, and simplify the code a little. We can use a relaxed store because the mutex already provides sequential consistency. Also we don't need to check whether __addr == &_M_ver because we know that's always true for platforms that use a condition variable, and so we also know that we always need to use notify_all() not notify_one(). Reviewed-by: Thomas Rodgers <trodg...@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/106183 * include/bits/atomic_wait.h (__waiter_pool_base::_M_notify): Move increment of _M_ver here. [!_GLIBCXX_HAVE_PLATFORM_WAIT]: Lock mutex around increment. Use relaxed memory order and always notify all waiters. (__waiter_base::_M_do_wait) [!_GLIBCXX_HAVE_PLATFORM_WAIT]: Check value again after locking mutex. (__waiter_base::_M_notify): Remove increment of _M_ver. (cherry picked from commit af98cb88eb4be6a1668ddf966e975149bf8610b1)
