about summary refs log tree commit diff
path: root/linuxthreads/spinlock.h
blob: 17efd183cd3691e9b8d5be8285e25eac4000f046 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
/* Linuxthreads - a simple clone()-based implementation of Posix        */
/* threads for Linux.                                                   */
/* Copyright (C) 1998 Xavier Leroy (Xavier.Leroy@inria.fr)              */
/*                                                                      */
/* This program is free software; you can redistribute it and/or        */
/* modify it under the terms of the GNU Library General Public License  */
/* as published by the Free Software Foundation; either version 2       */
/* of the License, or (at your option) any later version.               */
/*                                                                      */
/* This program is distributed in the hope that it will be useful,      */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of       */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
/* GNU Library General Public License for more details.                 */


/* There are 2 compare and swap synchronization primitives with
   different semantics:

	1. compare_and_swap, which has acquire semantics (i.e. it
	completes befor subsequent writes.)
	2. compare_and_swap_with_release_semantics, which has release
	semantics (it completes after previous writes.)

   For those platforms on which they are the same. HAS_COMPARE_AND_SWAP
   should be defined. For those platforms on which they are different,
   HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS has to be defined.  */

#ifndef HAS_COMPARE_AND_SWAP
#ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
#define HAS_COMPARE_AND_SWAP
#endif
#endif

#if defined(TEST_FOR_COMPARE_AND_SWAP)

extern int __pthread_has_cas;
extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
                                      int * spinlock);

static inline int compare_and_swap(long * ptr, long oldval, long newval,
                                   int * spinlock)
{
  if (__builtin_expect (__pthread_has_cas, 1))
    return __compare_and_swap(ptr, oldval, newval);
  else
    return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
}

#elif defined(HAS_COMPARE_AND_SWAP)

#ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS

static inline int
compare_and_swap_with_release_semantics (long * ptr, long oldval,
					 long newval, int * spinlock)
{
  return __compare_and_swap_with_release_semantics (ptr, oldval,
						    newval);
}

#endif

static inline int compare_and_swap(long * ptr, long oldval, long newval,
                                   int * spinlock)
{
  return __compare_and_swap(ptr, oldval, newval);
}

#else

extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
                                      int * spinlock);

static inline int compare_and_swap(long * ptr, long oldval, long newval,
                                   int * spinlock)
{
  return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
}

#endif

#ifndef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
#define compare_and_swap_with_release_semantics compare_and_swap
#define __compare_and_swap_with_release_semantics __compare_and_swap
#endif

/* Internal locks */

extern void internal_function __pthread_lock(struct _pthread_fastlock * lock,
					     pthread_descr self);
extern int __pthread_unlock(struct _pthread_fastlock *lock);

static inline void __pthread_init_lock(struct _pthread_fastlock * lock)
{
  lock->__status = 0;
  lock->__spinlock = 0;
}

static inline int __pthread_trylock (struct _pthread_fastlock * lock)
{
#if defined HAS_COMPARE_AND_SWAP
  long oldstatus;
#endif

#if defined TEST_FOR_COMPARE_AND_SWAP
  if (!__pthread_has_cas)
#endif
#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
  {
    return (testandset(&lock->__spinlock) ? EBUSY : 0);
  }
#endif

#if defined HAS_COMPARE_AND_SWAP
  do {
    oldstatus = lock->__status;
    if (oldstatus != 0) return EBUSY;
  } while(! __compare_and_swap(&lock->__status, 0, 1));
  return 0;
#endif
}

/* Variation of internal lock used for pthread_mutex_t, supporting
   timed-out waits.  Warning: do not mix these operations with the above ones
   over the same lock object! */

extern void __pthread_alt_lock(struct _pthread_fastlock * lock,
			       pthread_descr self);

extern int __pthread_alt_timedlock(struct _pthread_fastlock * lock,
			       pthread_descr self, const struct timespec *abstime);

extern void __pthread_alt_unlock(struct _pthread_fastlock *lock);

static inline void __pthread_alt_init_lock(struct _pthread_fastlock * lock)
{
  lock->__status = 0;
  lock->__spinlock = 0;
}

static inline int __pthread_alt_trylock (struct _pthread_fastlock * lock)
{
#if defined HAS_COMPARE_AND_SWAP
  long oldstatus;
#endif

#if defined TEST_FOR_COMPARE_AND_SWAP
  if (!__pthread_has_cas)
#endif
#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
  {
    return (testandset(&lock->__spinlock) ? EBUSY : 0);
  }
#endif

#if defined HAS_COMPARE_AND_SWAP
  do {
    oldstatus = lock->__status;
    if (oldstatus != 0) return EBUSY;
  } while(! compare_and_swap(&lock->__status, 0, 1, &lock->__spinlock));
  return 0;
#endif
}

/* Initializers for both lock variants */

#define LOCK_INITIALIZER {0, 0}
#define ALT_LOCK_INITIALIZER {0, 0}

/* Operations on pthread_atomic, which is defined in internals.h */

static inline long atomic_increment(struct pthread_atomic *pa)
{
    long oldval;

    do {
	oldval = pa->p_count;
    } while (!compare_and_swap(&pa->p_count, oldval, oldval + 1, &pa->p_spinlock));

    return oldval;
}


static inline long atomic_decrement(struct pthread_atomic *pa)
{
    long oldval;

    do {
	oldval = pa->p_count;
    } while (!compare_and_swap(&pa->p_count, oldval, oldval - 1, &pa->p_spinlock));

    return oldval;
}

#define ATOMIC_INITIALIZER { 0, 0 }