1 /* Copyright (C) 2005 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 Lesser General Public License as published by 8 the Free Software Foundation; either version 2.1 of the License, or 9 (at your option) 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 Lesser General Public License for 14 more details. 15 16 You should have received a copy of the GNU Lesser General Public License 17 along with libgomp; see the file COPYING.LIB. If not, write to the 18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 19 MA 02110-1301, USA. */ 20 21 /* As a special exception, if you link this library with other files, some 22 of which are compiled with GCC, to produce an executable, this library 23 does not by itself cause the resulting executable to be covered by the 24 GNU General Public License. This exception does not however invalidate 25 any other reasons why the executable file might be covered by the GNU 26 General Public License. */ 27 28 /* This is a Linux specific implementation of a semaphore synchronization 29 mechanism for libgomp. This type is private to the library. This 30 implementation uses atomic instructions and the futex syscall. */ 31 32 #include "libgomp.h" 33 #include "futex.h" 34 35 36 void 37 gomp_sem_wait_slow (gomp_sem_t *sem) 38 { 39 while (1) 40 { 41 int val = __sync_val_compare_and_swap (sem, 0, -1); 42 if (val > 0) 43 { 44 if (__sync_bool_compare_and_swap (sem, val, val - 1)) 45 return; 46 } 47 futex_wait (sem, -1); 48 } 49 } 50 51 void 52 gomp_sem_post_slow (gomp_sem_t *sem) 53 { 54 int old, tmp = *sem, wake; 55 56 do 57 { 58 old = tmp; 59 wake = old > 0 ? old + 1 : 1; 60 tmp = __sync_val_compare_and_swap (sem, old, wake); 61 } 62 while (old != tmp); 63 64 futex_wake (sem, wake); 65 } 66