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
42void
43omp_init_lock (omp_lock_t *lock)
44{
45  gomp_mutex_init (lock);
46}
47
48void
49omp_destroy_lock (omp_lock_t *lock)
50{
51  gomp_mutex_destroy (lock);
52}
53
54void
55omp_set_lock (omp_lock_t *lock)
56{
57  gomp_mutex_lock (lock);
58}
59
60void
61omp_unset_lock (omp_lock_t *lock)
62{
63  gomp_mutex_unlock (lock);
64}
65
66int
67omp_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)
89static inline int gomp_tid (void)
90{
91  return syscall (SYS_gettid);
92}
93#elif !defined(__LP64__)
94static inline int gomp_tid (void)
95{
96  return (int) gomp_thread ();
97}
98#else
99static __thread int tid_cache;
100static 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
110void
111omp_init_nest_lock (omp_nest_lock_t *lock)
112{
113  memset (lock, 0, sizeof (lock));
114}
115
116void
117omp_destroy_nest_lock (omp_nest_lock_t *lock)
118{
119}
120
121void
122omp_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
144void
145omp_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
156int
157omp_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
173ialias (omp_init_lock)
174ialias (omp_init_nest_lock)
175ialias (omp_destroy_lock)
176ialias (omp_destroy_nest_lock)
177ialias (omp_set_lock)
178ialias (omp_set_nest_lock)
179ialias (omp_unset_lock)
180ialias (omp_unset_nest_lock)
181ialias (omp_test_lock)
182ialias (omp_test_nest_lock)
183