mutex.c revision 1.3
1/* Copyright (C) 2005-2013 Free Software Foundation, Inc. 2 Contributed by Richard Henderson <rth@redhat.com>. 3 4 This file is part of the GNU OpenMP Library (libgomp). 5 6 Libgomp is free software; you can redistribute it and/or modify it 7 under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3, or (at your option) 9 any later version. 10 11 Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 13 FOR A PARTICULAR PURPOSE. See the GNU General Public License for 14 more details. 15 16 Under Section 7 of GPL version 3, you are granted additional 17 permissions described in the GCC Runtime Library Exception, version 18 3.1, as published by the Free Software Foundation. 19 20 You should have received a copy of the GNU General Public License and 21 a copy of the GCC Runtime Library Exception along with this program; 22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 <http://www.gnu.org/licenses/>. */ 24 25/* This is a Linux specific implementation of a mutex synchronization 26 mechanism for libgomp. This type is private to the library. This 27 implementation uses atomic instructions and the futex syscall. */ 28 29#include "wait.h" 30 31long int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG; 32long int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG; 33 34void 35gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval) 36{ 37 /* First loop spins a while. */ 38 while (oldval == 1) 39 { 40 if (do_spin (mutex, 1)) 41 { 42 /* Spin timeout, nothing changed. Set waiting flag. */ 43 oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE); 44 if (oldval == 0) 45 return; 46 futex_wait (mutex, -1); 47 break; 48 } 49 else 50 { 51 /* Something changed. If now unlocked, we're good to go. */ 52 oldval = 0; 53 if (__atomic_compare_exchange_n (mutex, &oldval, 1, false, 54 MEMMODEL_ACQUIRE, MEMMODEL_RELAXED)) 55 return; 56 } 57 } 58 59 /* Second loop waits until mutex is unlocked. We always exit this 60 loop with wait flag set, so next unlock will awaken a thread. */ 61 while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE))) 62 do_wait (mutex, -1); 63} 64 65void 66gomp_mutex_unlock_slow (gomp_mutex_t *mutex) 67{ 68 futex_wake (mutex, 1); 69} 70