xref: /freebsd/lib/libc/gen/sem_new.c (revision aa64588d28258aef88cc33b8043112e8856948d0) 
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 
51 __weak_reference(_sem_close, sem_close);
52 __weak_reference(_sem_destroy, sem_destroy);
53 __weak_reference(_sem_getvalue, sem_getvalue);
54 __weak_reference(_sem_init, sem_init);
55 __weak_reference(_sem_open, sem_open);
56 __weak_reference(_sem_post, sem_post);
57 __weak_reference(_sem_timedwait, sem_timedwait);
58 __weak_reference(_sem_trywait, sem_trywait);
59 __weak_reference(_sem_unlink, sem_unlink);
60 __weak_reference(_sem_wait, sem_wait);
61 
62 #define SEM_PREFIX	"/tmp/SEMD"
63 #define SEM_MAGIC	((u_int32_t)0x73656d31)
64 
65 struct sem_nameinfo {
66 	int open_count;
67 	char *name;
68 	sem_t *sem;
69 	LIST_ENTRY(sem_nameinfo) next;
70 };
71 
72 static pthread_once_t once = PTHREAD_ONCE_INIT;
73 static pthread_mutex_t sem_llock;
74 static LIST_HEAD(,sem_nameinfo) sem_list = LIST_HEAD_INITIALIZER(sem_list);
75 
76 static void
77 sem_prefork()
78 {
79 
80 	_pthread_mutex_lock(&sem_llock);
81 }
82 
83 static void
84 sem_postfork()
85 {
86 	_pthread_mutex_unlock(&sem_llock);
87 }
88 
89 static void
90 sem_child_postfork()
91 {
92 	_pthread_mutex_unlock(&sem_llock);
93 }
94 
95 static void
96 sem_module_init(void)
97 {
98 	pthread_mutexattr_t ma;
99 
100 	_pthread_mutexattr_init(&ma);
101 	_pthread_mutexattr_settype(&ma,  PTHREAD_MUTEX_RECURSIVE);
102 	_pthread_mutex_init(&sem_llock, &ma);
103 	_pthread_mutexattr_destroy(&ma);
104 	_pthread_atfork(sem_prefork, sem_postfork, sem_child_postfork);
105 }
106 
107 static inline int
108 sem_check_validity(sem_t *sem)
109 {
110 
111 	if (sem->_magic == SEM_MAGIC)
112 		return (0);
113 	else {
114 		errno = EINVAL;
115 		return (-1);
116 	}
117 }
118 
119 int
120 _sem_init(sem_t *sem, int pshared, unsigned int value)
121 {
122 
123 	if (value > SEM_VALUE_MAX) {
124 		errno = EINVAL;
125 		return (-1);
126 	}
127 
128 	bzero(sem, sizeof(sem_t));
129 	sem->_magic = SEM_MAGIC;
130 	sem->_kern._count = (u_int32_t)value;
131 	sem->_kern._has_waiters = 0;
132 	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
133 	return (0);
134 }
135 
136 sem_t *
137 _sem_open(const char *name, int flags, ...)
138 {
139 	char path[PATH_MAX];
140 
141 	struct stat sb;
142 	va_list ap;
143 	struct sem_nameinfo *ni = NULL;
144 	sem_t *sem = NULL;
145 	int fd = -1, mode, len, errsave;
146 	int value = 0;
147 
148 	if (name[0] != '/') {
149 		errno = EINVAL;
150 		return (SEM_FAILED);
151 	}
152 	name++;
153 
154 	if (flags & ~(O_CREAT|O_EXCL)) {
155 		errno = EINVAL;
156 		return (SEM_FAILED);
157 	}
158 
159 	_pthread_once(&once, sem_module_init);
160 
161 	_pthread_mutex_lock(&sem_llock);
162 	LIST_FOREACH(ni, &sem_list, next) {
163 		if (strcmp(name, ni->name) == 0) {
164 			ni->open_count++;
165 			sem = ni->sem;
166 			_pthread_mutex_unlock(&sem_llock);
167 			return (sem);
168 		}
169 	}
170 
171 	if (flags & O_CREAT) {
172 		va_start(ap, flags);
173 		mode = va_arg(ap, int);
174 		value = va_arg(ap, int);
175 		va_end(ap);
176 	}
177 
178 	len = sizeof(*ni) + strlen(name) + 1;
179 	ni = (struct sem_nameinfo *)malloc(len);
180 	if (ni == NULL) {
181 		errno = ENOSPC;
182 		goto error;
183 	}
184 
185 	ni->name = (char *)(ni+1);
186 	strcpy(ni->name, name);
187 
188 	strcpy(path, SEM_PREFIX);
189 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
190 		errno = ENAMETOOLONG;
191 		goto error;
192 	}
193 
194 	fd = _open(path, flags|O_RDWR, mode);
195 	if (fd == -1)
196 		goto error;
197 	if (flock(fd, LOCK_EX) == -1)
198 		goto error;
199 	if (_fstat(fd, &sb)) {
200 		flock(fd, LOCK_UN);
201 		goto error;
202 	}
203 	if (sb.st_size < sizeof(sem_t)) {
204 		sem_t tmp;
205 
206 		tmp._magic = SEM_MAGIC;
207 		tmp._kern._has_waiters = 0;
208 		tmp._kern._count = value;
209 		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
210 		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
211 			flock(fd, LOCK_UN);
212 			goto error;
213 		}
214 	}
215 	flock(fd, LOCK_UN);
216 	sem = (sem_t *)mmap(NULL, sizeof(sem_t), PROT_READ|PROT_WRITE,
217 		MAP_SHARED|MAP_NOSYNC, fd, 0);
218 	if (sem == MAP_FAILED) {
219 		sem = NULL;
220 		if (errno == ENOMEM)
221 			errno = ENOSPC;
222 		goto error;
223 	}
224 	if (sem->_magic != SEM_MAGIC) {
225 		errno = EINVAL;
226 		goto error;
227 	}
228 	ni->open_count = 1;
229 	ni->sem = sem;
230 	LIST_INSERT_HEAD(&sem_list, ni, next);
231 	_pthread_mutex_unlock(&sem_llock);
232 	_close(fd);
233 	return (sem);
234 
235 error:
236 	errsave = errno;
237 	_pthread_mutex_unlock(&sem_llock);
238 	if (fd != -1)
239 		_close(fd);
240 	if (sem != NULL)
241 		munmap(sem, sizeof(sem_t));
242 	free(ni);
243 	errno = errsave;
244 	return (SEM_FAILED);
245 }
246 
247 int
248 _sem_close(sem_t *sem)
249 {
250 	struct sem_nameinfo *ni;
251 
252 	if (sem_check_validity(sem) != 0)
253 		return (-1);
254 
255 	if (!(sem->_kern._flags & SEM_NAMED)) {
256 		errno = EINVAL;
257 		return (-1);
258 	}
259 
260 	_pthread_once(&once, sem_module_init);
261 
262 	_pthread_mutex_lock(&sem_llock);
263 	LIST_FOREACH(ni, &sem_list, next) {
264 		if (sem == ni->sem) {
265 			if (--ni->open_count > 0) {
266 				_pthread_mutex_unlock(&sem_llock);
267 				return (0);
268 			}
269 			else
270 				break;
271 		}
272 	}
273 
274 	if (ni) {
275 		LIST_REMOVE(ni, next);
276 		_pthread_mutex_unlock(&sem_llock);
277 		munmap(sem, sizeof(*sem));
278 		free(ni);
279 		return (0);
280 	}
281 	_pthread_mutex_unlock(&sem_llock);
282 	errno = EINVAL;
283 	return (-1);
284 }
285 
286 int
287 _sem_unlink(const char *name)
288 {
289 	char path[PATH_MAX];
290 
291 	if (name[0] != '/') {
292 		errno = ENOENT;
293 		return -1;
294 	}
295 	name++;
296 
297 	strcpy(path, SEM_PREFIX);
298 	if (strlcat(path, name, sizeof(path)) >= sizeof(path)) {
299 		errno = ENAMETOOLONG;
300 		return (-1);
301 	}
302 	return unlink(path);
303 }
304 
305 int
306 _sem_destroy(sem_t *sem)
307 {
308 
309 	if (sem_check_validity(sem) != 0)
310 		return (-1);
311 
312 	if (sem->_kern._flags & SEM_NAMED) {
313 		errno = EINVAL;
314 		return (-1);
315 	}
316 	sem->_magic = 0;
317 	return (0);
318 }
319 
320 int
321 _sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
322 {
323 
324 	if (sem_check_validity(sem) != 0)
325 		return (-1);
326 
327 	*sval = (int)sem->_kern._count;
328 	return (0);
329 }
330 
331 static __inline int
332 usem_wake(struct _usem *sem)
333 {
334 	if (!sem->_has_waiters)
335 		return (0);
336 	return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
337 }
338 
339 static __inline int
340 usem_wait(struct _usem *sem, const struct timespec *timeout)
341 {
342 	if (timeout && (timeout->tv_sec < 0 || (timeout->tv_sec == 0 &&
343 	    timeout->tv_nsec <= 0))) {
344 		errno = ETIMEDOUT;
345 		return (-1);
346 	}
347 	return _umtx_op(sem, UMTX_OP_SEM_WAIT, 0, NULL,
348 			__DECONST(void*, timeout));
349 }
350 
351 int
352 _sem_trywait(sem_t *sem)
353 {
354 	int val;
355 
356 	if (sem_check_validity(sem) != 0)
357 		return (-1);
358 
359 	while ((val = sem->_kern._count) > 0) {
360 		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
361 			return (0);
362 	}
363 	errno = EAGAIN;
364 	return (-1);
365 }
366 
367 static void
368 sem_cancel_handler(void *arg)
369 {
370 	sem_t *sem = arg;
371 
372 	if (sem->_kern._has_waiters && sem->_kern._count)
373 		usem_wake(&sem->_kern);
374 }
375 
376 #define TIMESPEC_SUB(dst, src, val)                             \
377         do {                                                    \
378                 (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec;  \
379                 (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \
380                 if ((dst)->tv_nsec < 0) {                       \
381                         (dst)->tv_sec--;                        \
382                         (dst)->tv_nsec += 1000000000;           \
383                 }                                               \
384         } while (0)
385 
386 
387 static __inline int
388 enable_async_cancel(void)
389 {
390 	int old;
391 
392 	_pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &old);
393 	return (old);
394 }
395 
396 static __inline void
397 restore_async_cancel(int val)
398 {
399 	_pthread_setcanceltype(val, NULL);
400 }
401 
402 int
403 _sem_timedwait(sem_t * __restrict sem,
404 	const struct timespec * __restrict abstime)
405 {
406 	struct timespec ts, ts2;
407 	int val, retval, saved_cancel;
408 
409 	if (sem_check_validity(sem) != 0)
410 		return (-1);
411 
412 	retval = 0;
413 	for (;;) {
414 		while ((val = sem->_kern._count) > 0) {
415 			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
416 				return (0);
417 		}
418 
419 		if (retval)
420 			break;
421 
422 		/*
423 		 * The timeout argument is only supposed to
424 		 * be checked if the thread would have blocked.
425 		 */
426 		if (abstime != NULL) {
427 			if (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0) {
428 				errno = EINVAL;
429 				return (-1);
430 			}
431 			clock_gettime(CLOCK_REALTIME, &ts);
432 			TIMESPEC_SUB(&ts2, abstime, &ts);
433 		}
434 		pthread_cleanup_push(sem_cancel_handler, sem);
435 		saved_cancel = enable_async_cancel();
436 		retval = usem_wait(&sem->_kern, abstime ? &ts2 : NULL);
437 		restore_async_cancel(saved_cancel);
438 		pthread_cleanup_pop(0);
439 	}
440 	return (retval);
441 }
442 
443 int
444 _sem_wait(sem_t *sem)
445 {
446 	return _sem_timedwait(sem, NULL);
447 }
448 
449 /*
450  * POSIX:
451  * The sem_post() interface is reentrant with respect to signals and may be
452  * invoked from a signal-catching function.
453  * The implementation does not use lock, so it should be safe.
454  */
455 int
456 _sem_post(sem_t *sem)
457 {
458 
459 	if (sem_check_validity(sem) != 0)
460 		return (-1);
461 
462 	atomic_add_rel_int(&sem->_kern._count, 1);
463 	return usem_wake(&sem->_kern);
464 }
465