|
131
|
1 /* Copyright (C) 2005-2018 Free Software Foundation, Inc.
|
|
0
|
2 Contributed by Richard Henderson <rth@redhat.com>.
|
|
|
3
|
|
111
|
4 This file is part of the GNU Offloading and Multi Processing Library
|
|
|
5 (libgomp).
|
|
0
|
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 semaphore synchronization
|
|
|
27 mechanism for libgomp. This type is private to the library. This
|
|
111
|
28 counting semaphore implementation uses atomic instructions and the
|
|
|
29 futex syscall, and a single 32-bit int to store semaphore state.
|
|
|
30 The low 31 bits are the count, the top bit is a flag set when some
|
|
|
31 threads may be waiting. */
|
|
0
|
32
|
|
|
33 #ifndef GOMP_SEM_H
|
|
|
34 #define GOMP_SEM_H 1
|
|
|
35
|
|
111
|
36 #include <limits.h> /* For INT_MIN */
|
|
|
37
|
|
0
|
38 typedef int gomp_sem_t;
|
|
111
|
39 #define SEM_WAIT INT_MIN
|
|
|
40 #define SEM_INC 1
|
|
0
|
41
|
|
111
|
42 extern void gomp_sem_wait_slow (gomp_sem_t *, int);
|
|
|
43 extern void gomp_sem_post_slow (gomp_sem_t *);
|
|
|
44
|
|
|
45 static inline void
|
|
|
46 gomp_sem_init (gomp_sem_t *sem, int value)
|
|
0
|
47 {
|
|
111
|
48 *sem = value * SEM_INC;
|
|
0
|
49 }
|
|
|
50
|
|
111
|
51 static inline void
|
|
|
52 gomp_sem_destroy (gomp_sem_t *sem)
|
|
0
|
53 {
|
|
|
54 }
|
|
|
55
|
|
111
|
56 static inline void
|
|
|
57 gomp_sem_wait (gomp_sem_t *sem)
|
|
|
58 {
|
|
|
59 int count = *sem;
|
|
|
60
|
|
|
61 while ((count & ~SEM_WAIT) != 0)
|
|
|
62 if (__atomic_compare_exchange_n (sem, &count, count - SEM_INC, true,
|
|
|
63 MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
|
|
|
64 return;
|
|
|
65 gomp_sem_wait_slow (sem, count);
|
|
|
66 }
|
|
|
67
|
|
|
68 static inline void
|
|
|
69 gomp_sem_post (gomp_sem_t *sem)
|
|
|
70 {
|
|
|
71 int count = *sem;
|
|
|
72
|
|
|
73 /* Clear SEM_WAIT here so that if there are no more waiting threads
|
|
|
74 we transition back to the uncontended state that does not make
|
|
|
75 futex syscalls. If there are waiting threads then when one is
|
|
|
76 awoken it will set SEM_WAIT again, so other waiting threads are
|
|
|
77 woken on a future gomp_sem_post. Furthermore, the awoken thread
|
|
|
78 will wake other threads in case gomp_sem_post was called again
|
|
|
79 before it had time to set SEM_WAIT. */
|
|
|
80 while (!__atomic_compare_exchange_n (sem, &count,
|
|
|
81 (count + SEM_INC) & ~SEM_WAIT, true,
|
|
|
82 MEMMODEL_RELEASE, MEMMODEL_RELAXED))
|
|
|
83 continue;
|
|
|
84
|
|
|
85 if (__builtin_expect (count & SEM_WAIT, 0))
|
|
|
86 gomp_sem_post_slow (sem);
|
|
|
87 }
|
|
0
|
88 #endif /* GOMP_SEM_H */
|
