sem_new.c revision 213153 
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 213153 2010-09-25 01:57:47Z davidxu $
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			ni->open_count++;
166			sem = ni->sem;
167			_pthread_mutex_unlock(&sem_llock);
168			return (sem);
169		}
170	}
171
172	if (flags & O_CREAT) {
173		va_start(ap, flags);
174		mode = va_arg(ap, int);
175		value = va_arg(ap, int);
176		va_end(ap);
177	}
178
179	len = sizeof(*ni) + strlen(name) + 1;
180	ni = (struct sem_nameinfo *)malloc(len);
181	if (ni == NULL) {
182		errno = ENOSPC;
183		goto error;
184	}
185
186	ni->name = (char *)(ni+1);
187	strcpy(ni->name, name);
188
189	strcpy(path, SEM_PREFIX);
190	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
191		errno = ENAMETOOLONG;
192		goto error;
193	}
194
195	fd = _open(path, flags|O_RDWR, mode);
196	if (fd == -1)
197		goto error;
198	if (flock(fd, LOCK_EX) == -1)
199		goto error;
200	if (_fstat(fd, &sb)) {
201		flock(fd, LOCK_UN);
202		goto error;
203	}
204	if (sb.st_size < sizeof(sem_t)) {
205		sem_t tmp;
206
207		tmp._magic = SEM_MAGIC;
208		tmp._kern._has_waiters = 0;
209		tmp._kern._count = value;
210		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
211		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
212			flock(fd, LOCK_UN);
213			goto error;
214		}
215	}
216	flock(fd, LOCK_UN);
217	sem = (sem_t *)mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE,
218		MAP_SHARED|MAP_NOSYNC, fd, 0);
219	if (sem == MAP_FAILED) {
220		sem = NULL;
221		if (errno == ENOMEM)
222			errno = ENOSPC;
223		goto error;
224	}
225	if (sem->_magic != SEM_MAGIC) {
226		errno = EINVAL;
227		goto error;
228	}
229	ni->open_count = 1;
230	ni->sem = sem;
231	LIST_INSERT_HEAD(&sem_list, ni, next);
232	_pthread_mutex_unlock(&sem_llock);
233	_close(fd);
234	return (sem);
235
236error:
237	errsave = errno;
238	_pthread_mutex_unlock(&sem_llock);
239	if (fd != -1)
240		_close(fd);
241	if (sem != NULL)
242		munmap(sem, sizeof(sem_t));
243	free(ni);
244	errno = errsave;
245	return (SEM_FAILED);
246}
247
248int
249_sem_close(sem_t *sem)
250{
251	struct sem_nameinfo *ni;
252
253	if (sem_check_validity(sem) != 0)
254		return (-1);
255
256	if (!(sem->_kern._flags & SEM_NAMED)) {
257		errno = EINVAL;
258		return (-1);
259	}
260
261	_pthread_once(&once, sem_module_init);
262
263	_pthread_mutex_lock(&sem_llock);
264	LIST_FOREACH(ni, &sem_list, next) {
265		if (sem == ni->sem) {
266			if (--ni->open_count > 0) {
267				_pthread_mutex_unlock(&sem_llock);
268				return (0);
269			}
270			else
271				break;
272		}
273	}
274
275	if (ni) {
276		LIST_REMOVE(ni, next);
277		_pthread_mutex_unlock(&sem_llock);
278		munmap(sem, sizeof(*sem));
279		free(ni);
280		return (0);
281	}
282	_pthread_mutex_unlock(&sem_llock);
283	errno = EINVAL;
284	return (-1);
285}
286
287int
288_sem_unlink(const char *name)
289{
290	char path[PATH_MAX];
291
292	if (name[0] != '/') {
293		errno = ENOENT;
294		return -1;
295	}
296	name++;
297
298	strcpy(path, SEM_PREFIX);
299	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
300		errno = ENAMETOOLONG;
301		return (-1);
302	}
303	return unlink(path);
304}
305
306int
307_sem_destroy(sem_t *sem)
308{
309
310	if (sem_check_validity(sem) != 0)
311		return (-1);
312
313	if (sem->_kern._flags & SEM_NAMED) {
314		errno = EINVAL;
315		return (-1);
316	}
317	sem->_magic = 0;
318	return (0);
319}
320
321int
322_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
323{
324
325	if (sem_check_validity(sem) != 0)
326		return (-1);
327
328	*sval = (int)sem->_kern._count;
329	return (0);
330}
331
332static __inline int
333usem_wake(struct _usem *sem)
334{
335	if (!sem->_has_waiters)
336		return (0);
337	return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
338}
339
340static __inline int
341usem_wait(struct _usem *sem, const struct timespec *timeout)
342{
343	if (timeout && (timeout->tv_sec < 0 || (timeout->tv_sec == 0 &&
344	    timeout->tv_nsec <= 0))) {
345		errno = ETIMEDOUT;
346		return (-1);
347	}
348	return _umtx_op(sem, UMTX_OP_SEM_WAIT, 0, NULL,
349			__DECONST(void*, timeout));
350}
351
352int
353_sem_trywait(sem_t *sem)
354{
355	int val;
356
357	if (sem_check_validity(sem) != 0)
358		return (-1);
359
360	while ((val = sem->_kern._count) > 0) {
361		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
362			return (0);
363	}
364	errno = EAGAIN;
365	return (-1);
366}
367
368#define TIMESPEC_SUB(dst, src, val)                             \
369        do {                                                    \
370                (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec;  \
371                (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \
372                if ((dst)->tv_nsec < 0) {                       \
373                        (dst)->tv_sec--;                        \
374                        (dst)->tv_nsec += 1000000000;           \
375                }                                               \
376        } while (0)
377
378
379int
380_sem_timedwait(sem_t * __restrict sem,
381	const struct timespec * __restrict abstime)
382{
383	struct timespec ts, ts2;
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			clock_gettime(CLOCK_REALTIME, &ts);
411			TIMESPEC_SUB(&ts2, abstime, &ts);
412		}
413		_pthread_cancel_enter(1);
414		retval = usem_wait(&sem->_kern, abstime ? &ts2 : NULL);
415		_pthread_cancel_leave(0);
416	}
417	return (retval);
418}
419
420int
421_sem_wait(sem_t *sem)
422{
423	return _sem_timedwait(sem, NULL);
424}
425
426/*
427 * POSIX:
428 * The sem_post() interface is reentrant with respect to signals and may be
429 * invoked from a signal-catching function.
430 * The implementation does not use lock, so it should be safe.
431 */
432int
433_sem_post(sem_t *sem)
434{
435
436	if (sem_check_validity(sem) != 0)
437		return (-1);
438
439	atomic_add_rel_int(&sem->_kern._count, 1);
440	return usem_wake(&sem->_kern);
441}
442