1/* Copyright (C) 2005-2022 Free Software Foundation, Inc. 2 Contributed by Richard Henderson <rth@redhat.com>. 3 4 This file is part of the GNU Offloading and Multi Processing Library 5 (libgomp). 6 7 Libgomp is free software; you can redistribute it and/or modify it 8 under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 3, or (at your option) 10 any later version. 11 12 Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY 13 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 14 FOR A PARTICULAR PURPOSE. See the GNU General Public License for 15 more details. 16 17 Under Section 7 of GPL version 3, you are granted additional 18 permissions described in the GCC Runtime Library Exception, version 19 3.1, as published by the Free Software Foundation. 20 21 You should have received a copy of the GNU General Public License and 22 a copy of the GCC Runtime Library Exception along with this program; 23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 24 <http://www.gnu.org/licenses/>. */ 25 26/* This is a Linux specific implementation of a mutex synchronization 27 mechanism for libgomp. This type is private to the library. This 28 implementation uses atomic instructions and the futex syscall. */ 29 30#include "wait.h" 31 32int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG; 33int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG; 34 35void 36gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval) 37{ 38 /* First loop spins a while. */ 39 while (oldval == 1) 40 { 41 if (do_spin (mutex, 1)) 42 { 43 /* Spin timeout, nothing changed. Set waiting flag. */ 44 oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE); 45 if (oldval == 0) 46 return; 47 futex_wait (mutex, -1); 48 break; 49 } 50 else 51 { 52 /* Something changed. If now unlocked, we're good to go. */ 53 oldval = 0; 54 if (__atomic_compare_exchange_n (mutex, &oldval, 1, false, 55 MEMMODEL_ACQUIRE, MEMMODEL_RELAXED)) 56 return; 57 } 58 } 59 60 /* Second loop waits until mutex is unlocked. We always exit this 61 loop with wait flag set, so next unlock will awaken a thread. */ 62 while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE))) 63 do_wait (mutex, -1); 64} 65 66void 67gomp_mutex_unlock_slow (gomp_mutex_t *mutex) 68{ 69 futex_wake (mutex, 1); 70} 71