semaphore.c revision a27d2baa0c1a2ec70f47ea9199b1dd6762c8a349 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28#include <semaphore.h>
29#include <errno.h>
30#include <sys/time.h>
31#include <sys/atomics.h>
32
33int sem_init(sem_t *sem, int pshared, unsigned int value)
34{
35    if (sem == NULL) {
36        errno = EINVAL;
37        return -1;
38    }
39
40    if (pshared != 0) {
41        errno = ENOSYS;
42        return -1;
43    }
44
45    sem->count = value;
46    return 0;
47}
48
49
50int sem_destroy(sem_t *sem)
51{
52    if (sem == NULL) {
53        errno = EINVAL;
54        return -1;
55    }
56    if (sem->count == 0) {
57        errno = EBUSY;
58        return -1;
59    }
60    return 0;
61}
62
63
64sem_t *sem_open(const char *name, int oflag, ...)
65{
66    name=name;
67    oflag=oflag;
68
69    errno = ENOSYS;
70    return SEM_FAILED;
71}
72
73
74int sem_close(sem_t *sem)
75{
76    if (sem == NULL) {
77        errno = EINVAL;
78        return -1;
79    }
80    errno = ENOSYS;
81    return -1;
82}
83
84
85int sem_unlink(const char * name)
86{
87    errno = ENOSYS;
88    return -1;
89}
90
91
92static int
93__atomic_dec_if_positive( volatile unsigned int*  pvalue )
94{
95    unsigned int  old;
96
97    do {
98        old = *pvalue;
99    }
100    while ( old != 0 && __atomic_cmpxchg( (int)old, (int)old-1, (volatile int*)pvalue ) != 0 );
101
102    return old;
103}
104
105int sem_wait(sem_t *sem)
106{
107    if (sem == NULL) {
108        errno = EINVAL;
109        return -1;
110    }
111
112    for (;;) {
113        if (__atomic_dec_if_positive(&sem->count))
114            break;
115
116        __futex_wait(&sem->count, 0, 0);
117    }
118    return 0;
119}
120
121int sem_post(sem_t *sem)
122{
123    if (sem == NULL)
124        return EINVAL;
125
126    if (__atomic_inc((volatile int*)&sem->count) == 0)
127        __futex_wake(&sem->count, 1);
128
129    return 0;
130}
131
132int  sem_trywait(sem_t *sem)
133{
134    if (sem == NULL) {
135        errno = EINVAL;
136        return -1;
137    }
138
139    if (__atomic_dec_if_positive(&sem->count) > 0) {
140        return 0;
141    } else {
142        return EAGAIN;
143    }
144}
145
146int  sem_getvalue(sem_t *sem, int *sval)
147{
148    if (sem == NULL || sval == NULL) {
149        errno = EINVAL;
150        return -1;
151    }
152
153    *sval = sem->count;
154    return 0;
155}
156