sem_new.c revision 234057 
1/*
2 * Copyright (C) 2010 David Xu <davidxu@freebsd.org>.
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 * 1. Redistributions of source code must retain the above copyright
9 *    notice(s), this list of conditions and the following disclaimer as
10 *    the first lines of this file unmodified other than the possible
11 *    addition of one or more copyright notices.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice(s), this list of conditions and the following disclaimer in
14 *    the documentation and/or other materials provided with the
15 *    distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
20 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
21 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
24 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
25 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
26 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
27 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 *
29 * $FreeBSD: head/lib/libc/gen/sem_new.c 234057 2012-04-09 14:17:22Z jilles $
30 */
31
32#include "namespace.h"
33#include <sys/types.h>
34#include <sys/queue.h>
35#include <sys/mman.h>
36#include <sys/stat.h>
37#include <errno.h>
38#include <machine/atomic.h>
39#include <sys/umtx.h>
40#include <limits.h>
41#include <fcntl.h>
42#include <pthread.h>
43#include <stdarg.h>
44#include <stdlib.h>
45#include <string.h>
46#include <time.h>
47#include <semaphore.h>
48#include <unistd.h>
49#include "un-namespace.h"
50#include "libc_private.h"
51
52__weak_reference(_sem_close, sem_close);
53__weak_reference(_sem_destroy, sem_destroy);
54__weak_reference(_sem_getvalue, sem_getvalue);
55__weak_reference(_sem_init, sem_init);
56__weak_reference(_sem_open, sem_open);
57__weak_reference(_sem_post, sem_post);
58__weak_reference(_sem_timedwait, sem_timedwait);
59__weak_reference(_sem_trywait, sem_trywait);
60__weak_reference(_sem_unlink, sem_unlink);
61__weak_reference(_sem_wait, sem_wait);
62
63#define SEM_PREFIX	"/tmp/SEMD"
64#define SEM_MAGIC	((u_int32_t)0x73656d31)
65
66struct sem_nameinfo {
67	int open_count;
68	char *name;
69	sem_t *sem;
70	LIST_ENTRY(sem_nameinfo) next;
71};
72
73static pthread_once_t once = PTHREAD_ONCE_INIT;
74static pthread_mutex_t sem_llock;
75static LIST_HEAD(,sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
76
77static void
78sem_prefork()
79{
80
81	_pthread_mutex_lock(&sem_llock);
82}
83
84static void
85sem_postfork()
86{
87	_pthread_mutex_unlock(&sem_llock);
88}
89
90static void
91sem_child_postfork()
92{
93	_pthread_mutex_unlock(&sem_llock);
94}
95
96static void
97sem_module_init(void)
98{
99	pthread_mutexattr_t ma;
100
101	_pthread_mutexattr_init(&ma);
102	_pthread_mutexattr_settype(&ma,  PTHREAD_MUTEX_RECURSIVE);
103	_pthread_mutex_init(&sem_llock, &ma);
104	_pthread_mutexattr_destroy(&ma);
105	_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
106}
107
108static inline int
109sem_check_validity(sem_t *sem)
110{
111
112	if (sem->_magic == SEM_MAGIC)
113		return (0);
114	else {
115		errno = EINVAL;
116		return (-1);
117	}
118}
119
120int
121_sem_init(sem_t *sem, int pshared, unsigned int value)
122{
123
124	if (value > SEM_VALUE_MAX) {
125		errno = EINVAL;
126		return (-1);
127	}
128
129	bzero(sem, sizeof(sem_t));
130	sem->_magic = SEM_MAGIC;
131	sem->_kern._count = (u_int32_t)value;
132	sem->_kern._has_waiters = 0;
133	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
134	return (0);
135}
136
137sem_t *
138_sem_open(const char *name, int flags, ...)
139{
140	char path[PATH_MAX];
141
142	struct stat sb;
143	va_list ap;
144	struct sem_nameinfo *ni = NULL;
145	sem_t *sem = NULL;
146	int fd = -1, mode, len, errsave;
147	int value = 0;
148
149	if (name[0] != '/') {
150		errno = EINVAL;
151		return (SEM_FAILED);
152	}
153	name++;
154
155	if (flags & ~(O_CREAT|O_EXCL)) {
156		errno = EINVAL;
157		return (SEM_FAILED);
158	}
159
160	_pthread_once(&once, sem_module_init);
161
162	_pthread_mutex_lock(&sem_llock);
163	LIST_FOREACH(ni, &sem_list, next) {
164		if (strcmp(name, ni->name) == 0) {
165			if ((flags & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL)) {
166				_pthread_mutex_unlock(&sem_llock);
167				errno = EEXIST;
168				return (SEM_FAILED);
169			} else {
170				ni->open_count++;
171				sem = ni->sem;
172				_pthread_mutex_unlock(&sem_llock);
173				return (sem);
174			}
175		}
176	}
177
178	if (flags & O_CREAT) {
179		va_start(ap, flags);
180		mode = va_arg(ap, int);
181		value = va_arg(ap, int);
182		va_end(ap);
183	}
184
185	len = sizeof(*ni) + strlen(name) + 1;
186	ni = (struct sem_nameinfo *)malloc(len);
187	if (ni == NULL) {
188		errno = ENOSPC;
189		goto error;
190	}
191
192	ni->name = (char *)(ni+1);
193	strcpy(ni->name, name);
194
195	strcpy(path, SEM_PREFIX);
196	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
197		errno = ENAMETOOLONG;
198		goto error;
199	}
200
201	fd = _open(path, flags|O_RDWR, mode);
202	if (fd == -1)
203		goto error;
204	if (flock(fd, LOCK_EX) == -1)
205		goto error;
206	if (_fstat(fd, &sb)) {
207		flock(fd, LOCK_UN);
208		goto error;
209	}
210	if (sb.st_size < sizeof(sem_t)) {
211		sem_t tmp;
212
213		tmp._magic = SEM_MAGIC;
214		tmp._kern._has_waiters = 0;
215		tmp._kern._count = value;
216		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
217		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
218			flock(fd, LOCK_UN);
219			goto error;
220		}
221	}
222	flock(fd, LOCK_UN);
223	sem = (sem_t *)mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE,
224		MAP_SHARED|MAP_NOSYNC, fd, 0);
225	if (sem == MAP_FAILED) {
226		sem = NULL;
227		if (errno == ENOMEM)
228			errno = ENOSPC;
229		goto error;
230	}
231	if (sem->_magic != SEM_MAGIC) {
232		errno = EINVAL;
233		goto error;
234	}
235	ni->open_count = 1;
236	ni->sem = sem;
237	LIST_INSERT_HEAD(&sem_list, ni, next);
238	_pthread_mutex_unlock(&sem_llock);
239	_close(fd);
240	return (sem);
241
242error:
243	errsave = errno;
244	_pthread_mutex_unlock(&sem_llock);
245	if (fd != -1)
246		_close(fd);
247	if (sem != NULL)
248		munmap(sem, sizeof(sem_t));
249	free(ni);
250	errno = errsave;
251	return (SEM_FAILED);
252}
253
254int
255_sem_close(sem_t *sem)
256{
257	struct sem_nameinfo *ni;
258
259	if (sem_check_validity(sem) != 0)
260		return (-1);
261
262	if (!(sem->_kern._flags & SEM_NAMED)) {
263		errno = EINVAL;
264		return (-1);
265	}
266
267	_pthread_once(&once, sem_module_init);
268
269	_pthread_mutex_lock(&sem_llock);
270	LIST_FOREACH(ni, &sem_list, next) {
271		if (sem == ni->sem) {
272			if (--ni->open_count > 0) {
273				_pthread_mutex_unlock(&sem_llock);
274				return (0);
275			}
276			else
277				break;
278		}
279	}
280
281	if (ni) {
282		LIST_REMOVE(ni, next);
283		_pthread_mutex_unlock(&sem_llock);
284		munmap(sem, sizeof(*sem));
285		free(ni);
286		return (0);
287	}
288	_pthread_mutex_unlock(&sem_llock);
289	errno = EINVAL;
290	return (-1);
291}
292
293int
294_sem_unlink(const char *name)
295{
296	char path[PATH_MAX];
297
298	if (name[0] != '/') {
299		errno = ENOENT;
300		return -1;
301	}
302	name++;
303
304	strcpy(path, SEM_PREFIX);
305	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
306		errno = ENAMETOOLONG;
307		return (-1);
308	}
309	return unlink(path);
310}
311
312int
313_sem_destroy(sem_t *sem)
314{
315
316	if (sem_check_validity(sem) != 0)
317		return (-1);
318
319	if (sem->_kern._flags & SEM_NAMED) {
320		errno = EINVAL;
321		return (-1);
322	}
323	sem->_magic = 0;
324	return (0);
325}
326
327int
328_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
329{
330
331	if (sem_check_validity(sem) != 0)
332		return (-1);
333
334	*sval = (int)sem->_kern._count;
335	return (0);
336}
337
338static __inline int
339usem_wake(struct _usem *sem)
340{
341	return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
342}
343
344static __inline int
345usem_wait(struct _usem *sem, const struct timespec *abstime)
346{
347	struct _umtx_time *tm_p, timeout;
348	size_t tm_size;
349
350	if (abstime == NULL) {
351		tm_p = NULL;
352		tm_size = 0;
353	} else {
354		timeout._clockid = CLOCK_REALTIME;
355		timeout._flags = UMTX_ABSTIME;
356		timeout._timeout = *abstime;
357		tm_p = &timeout;
358		tm_size = sizeof(timeout);
359	}
360	return _umtx_op(sem, UMTX_OP_SEM_WAIT, 0,
361		    (void *)tm_size, __DECONST(void*, tm_p));
362}
363
364int
365_sem_trywait(sem_t *sem)
366{
367	int val;
368
369	if (sem_check_validity(sem) != 0)
370		return (-1);
371
372	while ((val = sem->_kern._count) > 0) {
373		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
374			return (0);
375	}
376	errno = EAGAIN;
377	return (-1);
378}
379
380int
381_sem_timedwait(sem_t * __restrict sem,
382	const struct timespec * __restrict abstime)
383{
384	int val, retval;
385
386	if (sem_check_validity(sem) != 0)
387		return (-1);
388
389	retval = 0;
390	for (;;) {
391		while ((val = sem->_kern._count) > 0) {
392			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
393				return (0);
394		}
395
396		if (retval) {
397			_pthread_testcancel();
398			break;
399		}
400
401		/*
402		 * The timeout argument is only supposed to
403		 * be checked if the thread would have blocked.
404		 */
405		if (abstime != NULL) {
406			if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) {
407				errno = EINVAL;
408				return (-1);
409			}
410		}
411		_pthread_cancel_enter(1);
412		retval = usem_wait(&sem->_kern, abstime);
413		_pthread_cancel_leave(0);
414	}
415	return (retval);
416}
417
418int
419_sem_wait(sem_t *sem)
420{
421	return _sem_timedwait(sem, NULL);
422}
423
424/*
425 * POSIX:
426 * The sem_post() interface is reentrant with respect to signals and may be
427 * invoked from a signal-catching function.
428 * The implementation does not use lock, so it should be safe.
429 */
430int
431_sem_post(sem_t *sem)
432{
433	unsigned int count;
434
435	if (sem_check_validity(sem) != 0)
436		return (-1);
437
438	do {
439		count = sem->_kern._count;
440		if (count + 1 > SEM_VALUE_MAX)
441			return (EOVERFLOW);
442	} while(!atomic_cmpset_rel_int(&sem->_kern._count, count, count+1));
443	(void)usem_wake(&sem->_kern);
444	return (0);
445}
446