xref: /freebsd/lib/libc/gen/sem_new.c (revision ad30f8e79bd1007cc2476e491bd21b4f5e389e0a) 
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  * $FreeBSD$
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 
66 struct sem_nameinfo {
67 	int open_count;
68 	char *name;
69 	sem_t *sem;
70 	LIST_ENTRY(sem_nameinfo) next;
71 };
72 
73 static pthread_once_t once = PTHREAD_ONCE_INIT;
74 static pthread_mutex_t sem_llock;
75 static LIST_HEAD(,sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
76 
77 static void
78 sem_prefork()
79 {
80 
81 	_pthread_mutex_lock(&sem_llock);
82 }
83 
84 static void
85 sem_postfork()
86 {
87 	_pthread_mutex_unlock(&sem_llock);
88 }
89 
90 static void
91 sem_child_postfork()
92 {
93 	_pthread_mutex_unlock(&sem_llock);
94 }
95 
96 static void
97 sem_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 
108 static inline int
109 sem_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 
120 int
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 
137 sem_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 
236 error:
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 
248 int
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 
287 int
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 
306 int
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 
321 int
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 
332 static __inline int
333 usem_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 
340 static __inline int
341 usem_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 
352 int
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 
379 int
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 
420 int
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  */
432 int
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