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 the public OpenMP locking
29 primitives. This implementation uses atomic instructions and the futex
30 syscall. */
31
32 #include "libgomp.h"
33 #include <string.h>
34 #include <unistd.h>
35 #include <sys/syscall.h>
36 #include "futex.h"
37
38
39 /* The internal gomp_mutex_t and the external non-recursive omp_lock_t
40 have the same form. Re-use it. */
41
42 void
omp_init_lock(omp_lock_t * lock)43 omp_init_lock (omp_lock_t *lock)
44 {
45 gomp_mutex_init (lock);
46 }
47
48 void
omp_destroy_lock(omp_lock_t * lock)49 omp_destroy_lock (omp_lock_t *lock)
50 {
51 gomp_mutex_destroy (lock);
52 }
53
54 void
omp_set_lock(omp_lock_t * lock)55 omp_set_lock (omp_lock_t *lock)
56 {
57 gomp_mutex_lock (lock);
58 }
59
60 void
omp_unset_lock(omp_lock_t * lock)61 omp_unset_lock (omp_lock_t *lock)
62 {
63 gomp_mutex_unlock (lock);
64 }
65
66 int
omp_test_lock(omp_lock_t * lock)67 omp_test_lock (omp_lock_t *lock)
68 {
69 return __sync_bool_compare_and_swap (lock, 0, 1);
70 }
71
72 /* The external recursive omp_nest_lock_t form requires additional work. */
73
74 /* We need an integer to uniquely identify this thread. Most generally
75 this is the thread's TID, which ideally we'd get this straight from
76 the TLS block where glibc keeps it. Unfortunately, we can't get at
77 that directly.
78
79 If we don't support (or have disabled) TLS, one function call is as
80 good (or bad) as any other. Use the syscall all the time.
81
82 On an ILP32 system (defined here as not LP64), we can make do with
83 any thread-local pointer. Ideally we'd use the TLS base address,
84 since that requires the least amount of arithmetic, but that's not
85 always available directly. Make do with the gomp_thread pointer
86 since it's handy. */
87
88 #if !defined (HAVE_TLS)
gomp_tid(void)89 static inline int gomp_tid (void)
90 {
91 return syscall (SYS_gettid);
92 }
93 #elif !defined(__LP64__)
gomp_tid(void)94 static inline int gomp_tid (void)
95 {
96 return (int) gomp_thread ();
97 }
98 #else
99 static __thread int tid_cache;
gomp_tid(void)100 static inline int gomp_tid (void)
101 {
102 int tid = tid_cache;
103 if (__builtin_expect (tid == 0, 0))
104 tid_cache = tid = syscall (SYS_gettid);
105 return tid;
106 }
107 #endif
108
109
110 void
omp_init_nest_lock(omp_nest_lock_t * lock)111 omp_init_nest_lock (omp_nest_lock_t *lock)
112 {
113 memset (lock, 0, sizeof (lock));
114 }
115
116 void
omp_destroy_nest_lock(omp_nest_lock_t * lock)117 omp_destroy_nest_lock (omp_nest_lock_t *lock)
118 {
119 }
120
121 void
omp_set_nest_lock(omp_nest_lock_t * lock)122 omp_set_nest_lock (omp_nest_lock_t *lock)
123 {
124 int otid, tid = gomp_tid ();
125
126 while (1)
127 {
128 otid = __sync_val_compare_and_swap (&lock->owner, 0, tid);
129 if (otid == 0)
130 {
131 lock->count = 1;
132 return;
133 }
134 if (otid == tid)
135 {
136 lock->count++;
137 return;
138 }
139
140 futex_wait (&lock->owner, otid);
141 }
142 }
143
144 void
omp_unset_nest_lock(omp_nest_lock_t * lock)145 omp_unset_nest_lock (omp_nest_lock_t *lock)
146 {
147 /* ??? Validate that we own the lock here. */
148
149 if (--lock->count == 0)
150 {
151 __sync_lock_release (&lock->owner);
152 futex_wake (&lock->owner, 1);
153 }
154 }
155
156 int
omp_test_nest_lock(omp_nest_lock_t * lock)157 omp_test_nest_lock (omp_nest_lock_t *lock)
158 {
159 int otid, tid = gomp_tid ();
160
161 otid = __sync_val_compare_and_swap (&lock->owner, 0, tid);
162 if (otid == 0)
163 {
164 lock->count = 1;
165 return 1;
166 }
167 if (otid == tid)
168 return ++lock->count;
169
170 return 0;
171 }
172
173 ialias (omp_init_lock)
174 ialias (omp_init_nest_lock)
175 ialias (omp_destroy_lock)
176 ialias (omp_destroy_nest_lock)
177 ialias (omp_set_lock)
178 ialias (omp_set_nest_lock)
179 ialias (omp_unset_lock)
180 ialias (omp_unset_nest_lock)
181 ialias (omp_test_lock)
182 ialias (omp_test_nest_lock)
183