| /* Copyright (C) 2005-2022 Free Software Foundation, Inc. |
| Contributed by Richard Henderson <rth@redhat.com>. |
| |
| This file is part of the GNU Offloading and Multi Processing Library |
| (libgomp). |
| |
| Libgomp is free software; you can redistribute it and/or modify it |
| under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 3, or (at your option) |
| any later version. |
| |
| Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY |
| WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS |
| FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
| more details. |
| |
| Under Section 7 of GPL version 3, you are granted additional |
| permissions described in the GCC Runtime Library Exception, version |
| 3.1, as published by the Free Software Foundation. |
| |
| You should have received a copy of the GNU General Public License and |
| a copy of the GCC Runtime Library Exception along with this program; |
| see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| /* This is a Linux specific implementation of a mutex synchronization |
| mechanism for libgomp. This type is private to the library. This |
| implementation uses atomic instructions and the futex syscall. */ |
| |
| #include "wait.h" |
| |
| int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG; |
| int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG; |
| |
| void |
| gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval) |
| { |
| /* First loop spins a while. */ |
| while (oldval == 1) |
| { |
| if (do_spin (mutex, 1)) |
| { |
| /* Spin timeout, nothing changed. Set waiting flag. */ |
| oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE); |
| if (oldval == 0) |
| return; |
| futex_wait (mutex, -1); |
| break; |
| } |
| else |
| { |
| /* Something changed. If now unlocked, we're good to go. */ |
| oldval = 0; |
| if (__atomic_compare_exchange_n (mutex, &oldval, 1, false, |
| MEMMODEL_ACQUIRE, MEMMODEL_RELAXED)) |
| return; |
| } |
| } |
| |
| /* Second loop waits until mutex is unlocked. We always exit this |
| loop with wait flag set, so next unlock will awaken a thread. */ |
| while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE))) |
| do_wait (mutex, -1); |
| } |
| |
| void |
| gomp_mutex_unlock_slow (gomp_mutex_t *mutex) |
| { |
| futex_wake (mutex, 1); |
| } |