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0a8f4febf7
Fix synchronization issues in <stop_token>. Replace shared_ptr with _Stop_state_ref and a reference count embedded in the shared state. Replace std::mutex with spinlock using one bit of a std::atomic<> that also tracks whether a stop request has been made and how many stop_source objects share ownership of the state. PR libstdc++/92895 * include/std/stop_token (stop_token::stop_possible()): Call new _M_stop_possible() function. (stop_token::stop_requested()): Do not use stop_possible(). (stop_token::binary_semaphore): New class, as temporary stand-in for std::binary_semaphore. (stop_token::_Stop_cb::_M_callback): Add noexcept to type. (stop_token::_Stop_cb::_M_destroyed, stop_token::_Stop_cb::_M_done): New data members for symchronization with stop_callback destruction. (stop_token::_Stop_cb::_Stop_cb): Make non-template. (stop_token::_Stop_cb::_M_linked, stop_token::_Stop_cb::_S_execute): Remove. (stop_token::_Stop_cb::_M_run): New member function. (stop_token::_Stop_state::_M_stopped, stop_token::_Stop_state::_M_mtx): Remove. (stop_token::_Stop_state::_M_owners): New data member to track reference count for ownership. (stop_token::_Stop_state::_M_value): New data member combining a spinlock, the stop requested flag, and the reference count for associated stop_source objects. (stop_token::_Stop_state::_M_requester): New data member for synchronization with stop_callback destruction. (stop_token::_Stop_state::_M_stop_possible()): New member function. (stop_token::_Stop_state::_M_stop_requested()): Inspect relevant bit of _M_value. (stop_token::_Stop_state::_M_add_owner) (stop_token::_Stop_state::_M_release_ownership) (stop_token::_Stop_state::_M_add_ssrc) (stop_token::_Stop_state::_M_sub_ssrc): New member functions for updating reference counts. (stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock) (stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock) (stop_token::_Stop_state::_M_try_lock) (stop_token::_Stop_state::_M_try_lock_and_stop) (stop_token::_Stop_state::_M_do_try_lock): New member functions for managing spinlock. (stop_token::_Stop_state::_M_request_stop): Use atomic operations to read and update state. Release lock while running callbacks. Use new data members to synchronize with callback destruction. (stop_token::_Stop_state::_M_remove_callback): Likewise. (stop_token::_Stop_state::_M_register_callback): Use atomic operations to read and update state. (stop_token::_Stop_state_ref): Handle type to manage _Stop_state, replacing shared_ptr. (stop_source::stop_source(const stop_source&)): Update reference count. (stop_source::operator=(const stop_source&)): Likewise. (stop_source::~stop_source()): Likewise. (stop_source::stop_source(stop_source&&)): Define as defaulted. (stop_source::operator=(stop_source&&)): Establish postcondition on parameter. (stop_callback): Enforce preconditions on template parameter. Replace base class with data member of new _Cb_impl type. (stop_callback::stop_callback(const stop_token&, Cb&&)) (stop_callback::stop_callback(stop_token&&, Cb&&)): Fix TOCTTOU race. (stop_callback::_Cb_impl): New type wrapping _Callback member and defining the _S_execute member function. * testsuite/30_threads/stop_token/stop_callback/deadlock-mt.cc: New test. * testsuite/30_threads/stop_token/stop_callback/deadlock.cc: New test. * testsuite/30_threads/stop_token/stop_callback/destroy.cc: New test. * testsuite/30_threads/stop_token/stop_callback/destructible_neg.cc: New test. * testsuite/30_threads/stop_token/stop_callback/invocable_neg.cc: New test. * testsuite/30_threads/stop_token/stop_callback/invoke.cc: New test. * testsuite/30_threads/stop_token/stop_source/assign.cc: New test. * testsuite/30_threads/stop_token/stop_token/stop_possible.cc: New test.
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