1*404b540aSrobert /* Copyright (C) 2005 Free Software Foundation, Inc.
2*404b540aSrobert Contributed by Richard Henderson <rth@redhat.com>.
3*404b540aSrobert
4*404b540aSrobert This file is part of the GNU OpenMP Library (libgomp).
5*404b540aSrobert
6*404b540aSrobert Libgomp is free software; you can redistribute it and/or modify it
7*404b540aSrobert under the terms of the GNU Lesser General Public License as published by
8*404b540aSrobert the Free Software Foundation; either version 2.1 of the License, or
9*404b540aSrobert (at your option) any later version.
10*404b540aSrobert
11*404b540aSrobert Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
12*404b540aSrobert WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
13*404b540aSrobert FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
14*404b540aSrobert more details.
15*404b540aSrobert
16*404b540aSrobert You should have received a copy of the GNU Lesser General Public License
17*404b540aSrobert along with libgomp; see the file COPYING.LIB. If not, write to the
18*404b540aSrobert Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
19*404b540aSrobert MA 02110-1301, USA. */
20*404b540aSrobert
21*404b540aSrobert /* As a special exception, if you link this library with other files, some
22*404b540aSrobert of which are compiled with GCC, to produce an executable, this library
23*404b540aSrobert does not by itself cause the resulting executable to be covered by the
24*404b540aSrobert GNU General Public License. This exception does not however invalidate
25*404b540aSrobert any other reasons why the executable file might be covered by the GNU
26*404b540aSrobert General Public License. */
27*404b540aSrobert
28*404b540aSrobert /* This is a Linux specific implementation of a semaphore synchronization
29*404b540aSrobert mechanism for libgomp. This type is private to the library. This
30*404b540aSrobert implementation uses atomic instructions and the futex syscall. */
31*404b540aSrobert
32*404b540aSrobert #include "libgomp.h"
33*404b540aSrobert #include "futex.h"
34*404b540aSrobert
35*404b540aSrobert
36*404b540aSrobert void
gomp_sem_wait_slow(gomp_sem_t * sem)37*404b540aSrobert gomp_sem_wait_slow (gomp_sem_t *sem)
38*404b540aSrobert {
39*404b540aSrobert while (1)
40*404b540aSrobert {
41*404b540aSrobert int val = __sync_val_compare_and_swap (sem, 0, -1);
42*404b540aSrobert if (val > 0)
43*404b540aSrobert {
44*404b540aSrobert if (__sync_bool_compare_and_swap (sem, val, val - 1))
45*404b540aSrobert return;
46*404b540aSrobert }
47*404b540aSrobert futex_wait (sem, -1);
48*404b540aSrobert }
49*404b540aSrobert }
50*404b540aSrobert
51*404b540aSrobert void
gomp_sem_post_slow(gomp_sem_t * sem)52*404b540aSrobert gomp_sem_post_slow (gomp_sem_t *sem)
53*404b540aSrobert {
54*404b540aSrobert int old, tmp = *sem, wake;
55*404b540aSrobert
56*404b540aSrobert do
57*404b540aSrobert {
58*404b540aSrobert old = tmp;
59*404b540aSrobert wake = old > 0 ? old + 1 : 1;
60*404b540aSrobert tmp = __sync_val_compare_and_swap (sem, old, wake);
61*404b540aSrobert }
62*404b540aSrobert while (old != tmp);
63*404b540aSrobert
64*404b540aSrobert futex_wake (sem, wake);
65*404b540aSrobert }
66