[Bug libstdc++/92895] [libstdc++] stop_token conformance issues

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92895

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:0a8f4febf75e9e44f847b65776d7f5f38940b3bf

commit r10-6328-g0a8f4febf75e9e44f847b65776d7f5f38940b3bf
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jan 23 16:46:17 2020 +0000

    libstdc++: Fix conformance issues in <stop_token> (PR92895)

    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.