summaryrefslogtreecommitdiffstats
path: root/lib/libc/gen/sem.c
blob: 439f0fe5c41c42bbb4374d111303149d57cc7d25 (plain)
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
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
/*
 * Copyright (C) 2000 Jason Evans <jasone@freebsd.org>.
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice(s), this list of conditions and the following disclaimer as
 *    the first lines of this file unmodified other than the possible
 *    addition of one or more copyright notices.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice(s), this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * $FreeBSD$
 */

/*
 * Some notes about this implementation.
 *
 * This is mostly a simple implementation of POSIX semaphores that
 * does not need threading.  Any semaphore created is a kernel-based
 * semaphore regardless of the pshared attribute.  This is necessary
 * because libc's stub for pthread_cond_wait() doesn't really wait,
 * and it is not worth the effort impose this behavior on libc.
 *
 * All functions here are designed to be thread-safe so that a
 * threads library need not provide wrappers except to make
 * sem_wait() and sem_timedwait() cancellation points or to
 * provide a faster userland implementation for non-pshared
 * semaphores.
 *
 * Also, this implementation of semaphores cannot really support
 * real pshared semaphores.  The sem_t is an allocated object
 * and can't be seen by other processes when placed in shared
 * memory.  It should work across forks as long as the semaphore
 * is created before any forks.
 *
 * The function sem_init() should be overridden by a threads
 * library if it wants to provide a different userland version
 * of semaphores.  The functions sem_wait() and sem_timedwait()
 * need to be wrapped to provide cancellation points.  The function
 * sem_post() may need to be wrapped to be signal-safe.
 */
#include "namespace.h"
#include <sys/types.h>
#include <sys/queue.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdarg.h>
#include <stdlib.h>
#include <time.h>
#include <_semaphore.h>
#include "un-namespace.h"
#include "libc_private.h"

static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem);
static void  sem_free(sem_t sem);

static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(&named_sems);
static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER;

__weak_reference(__sem_init, sem_init);
__weak_reference(__sem_destroy, sem_destroy);
__weak_reference(__sem_open, sem_open);
__weak_reference(__sem_close, sem_close);
__weak_reference(__sem_unlink, sem_unlink);
__weak_reference(__sem_wait, sem_wait);
__weak_reference(__sem_trywait, sem_trywait);
__weak_reference(__sem_timedwait, sem_timedwait);
__weak_reference(__sem_post, sem_post);
__weak_reference(__sem_getvalue, sem_getvalue);


static inline int
sem_check_validity(sem_t *sem)
{

	if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC))
		return (0);
	else {
		errno = EINVAL;
		return (-1);
	}
}

static void
sem_free(sem_t sem)
{

	_pthread_mutex_destroy(&sem->lock);
	_pthread_cond_destroy(&sem->gtzero);
	sem->magic = 0;
	free(sem);
}

static sem_t
sem_alloc(unsigned int value, semid_t semid, int system_sem)
{
	sem_t sem;

	if (value > SEM_VALUE_MAX) {
		errno = EINVAL;
		return (NULL);
	}

	sem = (sem_t)malloc(sizeof(struct sem));
	if (sem == NULL) {
		errno = ENOSPC;
		return (NULL);
	}

	sem->count = (u_int32_t)value;
	sem->nwaiters = 0;
	sem->magic = SEM_MAGIC;
	sem->semid = semid;
	sem->syssem = system_sem;
	sem->lock = PTHREAD_MUTEX_INITIALIZER;
	sem->gtzero = PTHREAD_COND_INITIALIZER;
	return (sem);
}

int
__sem_init(sem_t *sem, int pshared, unsigned int value)
{
	semid_t semid;

	/*
	 * We always have to create the kernel semaphore if the
	 * threads library isn't present since libc's version of
	 * pthread_cond_wait() is just a stub that doesn't really
	 * wait.
	 */
	if (ksem_init(&semid, value) != 0)
		return (-1);

	(*sem) = sem_alloc(value, semid, 1);
	if ((*sem) == NULL) {
		ksem_destroy(semid);
		return (-1);
	}
	return (0);
}

int
__sem_destroy(sem_t *sem)
{
	int retval;

	if (sem_check_validity(sem) != 0)
		return (-1);

	_pthread_mutex_lock(&(*sem)->lock);
	/*
	 * If this is a system semaphore let the kernel track it otherwise
	 * make sure there are no waiters.
	 */
	if ((*sem)->syssem != 0)
		retval = ksem_destroy((*sem)->semid);
	else if ((*sem)->nwaiters > 0) {
		errno = EBUSY;
		retval = -1;
	}
	else {
		retval = 0;
		(*sem)->magic = 0;
	}
	_pthread_mutex_unlock(&(*sem)->lock);

	if (retval == 0) {
		_pthread_mutex_destroy(&(*sem)->lock);
		_pthread_cond_destroy(&(*sem)->gtzero);
		sem_free(*sem);
	}
	return (retval);
}

sem_t *
__sem_open(const char *name, int oflag, ...)
{
	sem_t *sem;
	sem_t s;
	semid_t semid;
	mode_t mode;
	unsigned int value;

	mode = 0;
	value = 0;

	if ((oflag & O_CREAT) != 0) {
		va_list ap;

		va_start(ap, oflag);
		mode = va_arg(ap, int);
		value = va_arg(ap, unsigned int);
		va_end(ap);
	}
	/*
	 * we can be lazy and let the kernel handle the "oflag",
	 * we'll just merge duplicate IDs into our list.
	 */
	if (ksem_open(&semid, name, oflag, mode, value) == -1)
		return (SEM_FAILED);
	/*
	 * search for a duplicate ID, we must return the same sem_t *
	 * if we locate one.
	 */
	_pthread_mutex_lock(&named_sems_mtx);
	LIST_FOREACH(s, &named_sems, entry) {
		if (s->semid == semid) {
			sem = s->backpointer;
			_pthread_mutex_unlock(&named_sems_mtx);
			return (sem);
		}
	}
	sem = (sem_t *)malloc(sizeof(*sem));
	if (sem == NULL)
		goto err;
	*sem = sem_alloc(value, semid, 1);
	if ((*sem) == NULL)
		goto err;
	LIST_INSERT_HEAD(&named_sems, *sem, entry);
	(*sem)->backpointer = sem;
	_pthread_mutex_unlock(&named_sems_mtx);
	return (sem);
err:
	_pthread_mutex_unlock(&named_sems_mtx);
	ksem_close(semid);
	if (sem != NULL) {
		if (*sem != NULL)
			sem_free(*sem);
		else
			errno = ENOSPC;
		free(sem);
	} else {
		errno = ENOSPC;
	}
	return (SEM_FAILED);
}

int
__sem_close(sem_t *sem)
{

	if (sem_check_validity(sem) != 0)
		return (-1);

	if ((*sem)->syssem == 0) {
		errno = EINVAL;
		return (-1);
	}

	_pthread_mutex_lock(&named_sems_mtx);
	if (ksem_close((*sem)->semid) != 0) {
		_pthread_mutex_unlock(&named_sems_mtx);
		return (-1);
	}
	LIST_REMOVE((*sem), entry);
	_pthread_mutex_unlock(&named_sems_mtx);
	sem_free(*sem);
	*sem = NULL;
	free(sem);
	return (0);
}

int
__sem_unlink(const char *name)
{

	return (ksem_unlink(name));
}

int
__sem_wait(sem_t *sem)
{

	if (sem_check_validity(sem) != 0)
		return (-1);

	return (ksem_wait((*sem)->semid));
}

int
__sem_trywait(sem_t *sem)
{
	int retval;

	if (sem_check_validity(sem) != 0)
		return (-1);

	if ((*sem)->syssem != 0)
 		retval = ksem_trywait((*sem)->semid);
	else {
		_pthread_mutex_lock(&(*sem)->lock);
		if ((*sem)->count > 0) {
			(*sem)->count--;
			retval = 0;
		} else {
			errno = EAGAIN;
			retval = -1;
		}
		_pthread_mutex_unlock(&(*sem)->lock);
	}
	return (retval);
}

int
__sem_timedwait(sem_t * __restrict sem,
    const struct timespec * __restrict abs_timeout)
{
	if (sem_check_validity(sem) != 0)
		return (-1);

	return (ksem_timedwait((*sem)->semid, abs_timeout));
}

int
__sem_post(sem_t *sem)
{

	if (sem_check_validity(sem) != 0)
		return (-1);

	return (ksem_post((*sem)->semid));
}

int
__sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
{
	int retval;

	if (sem_check_validity(sem) != 0)
		return (-1);

	if ((*sem)->syssem != 0)
		retval = ksem_getvalue((*sem)->semid, sval);
	else {
		_pthread_mutex_lock(&(*sem)->lock);
		*sval = (int)(*sem)->count;
		_pthread_mutex_unlock(&(*sem)->lock);

		retval = 0;
	}
	return (retval);
}
OpenPOWER on IntegriCloud