sem_new.c revision 294963 
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: stable/10/lib/libc/gen/sem_new.c 294963 2016-01-27 22:56:04Z 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	dev_t dev;
70	ino_t ino;
71	sem_t *sem;
72	LIST_ENTRY(sem_nameinfo) next;
73};
74
75static pthread_once_t once = PTHREAD_ONCE_INIT;
76static pthread_mutex_t sem_llock;
77static LIST_HEAD(,sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
78
79static void
80sem_prefork()
81{
82
83	_pthread_mutex_lock(&sem_llock);
84}
85
86static void
87sem_postfork()
88{
89	_pthread_mutex_unlock(&sem_llock);
90}
91
92static void
93sem_child_postfork()
94{
95	_pthread_mutex_unlock(&sem_llock);
96}
97
98static void
99sem_module_init(void)
100{
101	pthread_mutexattr_t ma;
102
103	_pthread_mutexattr_init(&ma);
104	_pthread_mutexattr_settype(&ma,  PTHREAD_MUTEX_RECURSIVE);
105	_pthread_mutex_init(&sem_llock, &ma);
106	_pthread_mutexattr_destroy(&ma);
107	_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
108}
109
110static inline int
111sem_check_validity(sem_t *sem)
112{
113
114	if (sem->_magic == SEM_MAGIC)
115		return (0);
116	else {
117		errno = EINVAL;
118		return (-1);
119	}
120}
121
122int
123_sem_init(sem_t *sem, int pshared, unsigned int value)
124{
125
126	if (value > SEM_VALUE_MAX) {
127		errno = EINVAL;
128		return (-1);
129	}
130
131	bzero(sem, sizeof(sem_t));
132	sem->_magic = SEM_MAGIC;
133	sem->_kern._count = (u_int32_t)value;
134	sem->_kern._has_waiters = 0;
135	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
136	return (0);
137}
138
139sem_t *
140_sem_open(const char *name, int flags, ...)
141{
142	char path[PATH_MAX];
143
144	struct stat sb;
145	va_list ap;
146	struct sem_nameinfo *ni = NULL;
147	sem_t *sem = NULL;
148	int fd = -1, mode, len, errsave;
149	int value = 0;
150
151	if (name[0] != '/') {
152		errno = EINVAL;
153		return (SEM_FAILED);
154	}
155	name++;
156	strcpy(path, SEM_PREFIX);
157	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
158		errno = ENAMETOOLONG;
159		return (SEM_FAILED);
160	}
161	if (flags & ~(O_CREAT|O_EXCL)) {
162		errno = EINVAL;
163		return (SEM_FAILED);
164	}
165	if ((flags & O_CREAT) != 0) {
166		va_start(ap, flags);
167		mode = va_arg(ap, int);
168		value = va_arg(ap, int);
169		va_end(ap);
170	}
171	fd = -1;
172	_pthread_once(&once, sem_module_init);
173
174	_pthread_mutex_lock(&sem_llock);
175	LIST_FOREACH(ni, &sem_list, next) {
176		if (ni->name != NULL && strcmp(name, ni->name) == 0) {
177			fd = _open(path, flags | O_RDWR | O_CLOEXEC |
178			    O_EXLOCK, mode);
179			if (fd == -1 || _fstat(fd, &sb) == -1) {
180				ni = NULL;
181				goto error;
182			}
183			if ((flags & (O_CREAT | O_EXCL)) == (O_CREAT |
184			    O_EXCL) || ni->dev != sb.st_dev ||
185			    ni->ino != sb.st_ino) {
186				ni->name = NULL;
187				ni = NULL;
188				break;
189			}
190			ni->open_count++;
191			sem = ni->sem;
192			_pthread_mutex_unlock(&sem_llock);
193			_close(fd);
194			return (sem);
195		}
196	}
197
198	len = sizeof(*ni) + strlen(name) + 1;
199	ni = (struct sem_nameinfo *)malloc(len);
200	if (ni == NULL) {
201		errno = ENOSPC;
202		goto error;
203	}
204
205	ni->name = (char *)(ni+1);
206	strcpy(ni->name, name);
207
208	if (fd == -1) {
209		fd = _open(path, flags | O_RDWR | O_CLOEXEC | O_EXLOCK, mode);
210		if (fd == -1 || _fstat(fd, &sb) == -1)
211			goto error;
212	}
213	if (sb.st_size < sizeof(sem_t)) {
214		sem_t tmp;
215
216		tmp._magic = SEM_MAGIC;
217		tmp._kern._has_waiters = 0;
218		tmp._kern._count = value;
219		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
220		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp))
221			goto error;
222	}
223	flock(fd, LOCK_UN);
224	sem = (sem_t *)mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE,
225		MAP_SHARED|MAP_NOSYNC, fd, 0);
226	if (sem == MAP_FAILED) {
227		sem = NULL;
228		if (errno == ENOMEM)
229			errno = ENOSPC;
230		goto error;
231	}
232	if (sem->_magic != SEM_MAGIC) {
233		errno = EINVAL;
234		goto error;
235	}
236	ni->open_count = 1;
237	ni->sem = sem;
238	ni->dev = sb.st_dev;
239	ni->ino = sb.st_ino;
240	LIST_INSERT_HEAD(&sem_list, ni, next);
241	_close(fd);
242	_pthread_mutex_unlock(&sem_llock);
243	return (sem);
244
245error:
246	errsave = errno;
247	if (fd != -1)
248		_close(fd);
249	if (sem != NULL)
250		munmap(sem, sizeof(sem_t));
251	free(ni);
252	_pthread_mutex_unlock(&sem_llock);
253	errno = errsave;
254	return (SEM_FAILED);
255}
256
257int
258_sem_close(sem_t *sem)
259{
260	struct sem_nameinfo *ni;
261
262	if (sem_check_validity(sem) != 0)
263		return (-1);
264
265	if (!(sem->_kern._flags & SEM_NAMED)) {
266		errno = EINVAL;
267		return (-1);
268	}
269
270	_pthread_once(&once, sem_module_init);
271
272	_pthread_mutex_lock(&sem_llock);
273	LIST_FOREACH(ni, &sem_list, next) {
274		if (sem == ni->sem) {
275			if (--ni->open_count > 0) {
276				_pthread_mutex_unlock(&sem_llock);
277				return (0);
278			}
279			else
280				break;
281		}
282	}
283
284	if (ni) {
285		LIST_REMOVE(ni, next);
286		_pthread_mutex_unlock(&sem_llock);
287		munmap(sem, sizeof(*sem));
288		free(ni);
289		return (0);
290	}
291	_pthread_mutex_unlock(&sem_llock);
292	errno = EINVAL;
293	return (-1);
294}
295
296int
297_sem_unlink(const char *name)
298{
299	char path[PATH_MAX];
300
301	if (name[0] != '/') {
302		errno = ENOENT;
303		return -1;
304	}
305	name++;
306	strcpy(path, SEM_PREFIX);
307	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
308		errno = ENAMETOOLONG;
309		return (-1);
310	}
311
312	return (unlink(path));
313}
314
315int
316_sem_destroy(sem_t *sem)
317{
318
319	if (sem_check_validity(sem) != 0)
320		return (-1);
321
322	if (sem->_kern._flags & SEM_NAMED) {
323		errno = EINVAL;
324		return (-1);
325	}
326	sem->_magic = 0;
327	return (0);
328}
329
330int
331_sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
332{
333
334	if (sem_check_validity(sem) != 0)
335		return (-1);
336
337	*sval = (int)sem->_kern._count;
338	return (0);
339}
340
341static __inline int
342usem_wake(struct _usem *sem)
343{
344	return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
345}
346
347static __inline int
348usem_wait(struct _usem *sem, const struct timespec *abstime)
349{
350	struct _umtx_time *tm_p, timeout;
351	size_t tm_size;
352
353	if (abstime == NULL) {
354		tm_p = NULL;
355		tm_size = 0;
356	} else {
357		timeout._clockid = CLOCK_REALTIME;
358		timeout._flags = UMTX_ABSTIME;
359		timeout._timeout = *abstime;
360		tm_p = &timeout;
361		tm_size = sizeof(timeout);
362	}
363	return _umtx_op(sem, UMTX_OP_SEM_WAIT, 0,
364		    (void *)tm_size, __DECONST(void*, tm_p));
365}
366
367int
368_sem_trywait(sem_t *sem)
369{
370	int val;
371
372	if (sem_check_validity(sem) != 0)
373		return (-1);
374
375	while ((val = sem->_kern._count) > 0) {
376		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
377			return (0);
378	}
379	errno = EAGAIN;
380	return (-1);
381}
382
383int
384_sem_timedwait(sem_t * __restrict sem,
385	const struct timespec * __restrict abstime)
386{
387	int val, retval;
388
389	if (sem_check_validity(sem) != 0)
390		return (-1);
391
392	retval = 0;
393	_pthread_testcancel();
394	for (;;) {
395		while ((val = sem->_kern._count) > 0) {
396			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
397				return (0);
398		}
399
400		if (retval) {
401			_pthread_testcancel();
402			break;
403		}
404
405		/*
406		 * The timeout argument is only supposed to
407		 * be checked if the thread would have blocked.
408		 */
409		if (abstime != NULL) {
410			if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) {
411				errno = EINVAL;
412				return (-1);
413			}
414		}
415		_pthread_cancel_enter(1);
416		retval = usem_wait(&sem->_kern, abstime);
417		_pthread_cancel_leave(0);
418	}
419	return (retval);
420}
421
422int
423_sem_wait(sem_t *sem)
424{
425	return _sem_timedwait(sem, NULL);
426}
427
428/*
429 * POSIX:
430 * The sem_post() interface is reentrant with respect to signals and may be
431 * invoked from a signal-catching function.
432 * The implementation does not use lock, so it should be safe.
433 */
434int
435_sem_post(sem_t *sem)
436{
437	unsigned int count;
438
439	if (sem_check_validity(sem) != 0)
440		return (-1);
441
442	do {
443		count = sem->_kern._count;
444		if (count + 1 > SEM_VALUE_MAX) {
445			errno = EOVERFLOW;
446			return (-1);
447		}
448	} while(!atomic_cmpset_rel_int(&sem->_kern._count, count, count+1));
449	(void)usem_wake(&sem->_kern);
450	return (0);
451}
452