1 /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
2 /* dbus-sysdeps-pthread.c Implements threads using pthreads (internal to libdbus)
3 *
4 * Copyright (C) 2002, 2003, 2006 Red Hat, Inc.
5 *
6 * Licensed under the Academic Free License version 2.1
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 *
22 */
23
24 #include <config.h>
25 #include "dbus-internals.h"
26 #include "dbus-sysdeps.h"
27 #include "dbus-threads.h"
28
29 #include <sys/time.h>
30 #include <pthread.h>
31 #include <string.h>
32
33 #ifdef HAVE_ERRNO_H
34 #include <errno.h>
35 #endif
36
37 #include <config.h>
38
39 /* Whether we have a "monotonic" clock; i.e. a clock not affected by
40 * changes in system time.
41 * This is initialized once in check_monotonic_clock below.
42 * https://bugs.freedesktop.org/show_bug.cgi?id=18121
43 */
44 static dbus_bool_t have_monotonic_clock = 0;
45
46 typedef struct {
47 pthread_mutex_t lock; /**< lock protecting count field */
48 volatile int count; /**< count of how many times lock holder has recursively locked */
49 volatile pthread_t holder; /**< holder of the lock if count >0,
50 valid but arbitrary thread if count
51 has ever been >0, uninitialized memory
52 if count has never been >0 */
53 } DBusMutexPThread;
54
55 typedef struct {
56 pthread_cond_t cond; /**< the condition */
57 } DBusCondVarPThread;
58
59 #define DBUS_MUTEX(m) ((DBusMutex*) m)
60 #define DBUS_MUTEX_PTHREAD(m) ((DBusMutexPThread*) m)
61
62 #define DBUS_COND_VAR(c) ((DBusCondVar*) c)
63 #define DBUS_COND_VAR_PTHREAD(c) ((DBusCondVarPThread*) c)
64
65
66 #ifdef DBUS_DISABLE_ASSERT
67 /* (tmp != 0) is a no-op usage to silence compiler */
68 #define PTHREAD_CHECK(func_name, result_or_call) \
69 do { int tmp = (result_or_call); if (tmp != 0) {;} } while (0)
70 #else
71 #define PTHREAD_CHECK(func_name, result_or_call) do { \
72 int tmp = (result_or_call); \
73 if (tmp != 0) { \
74 _dbus_warn_check_failed ("pthread function %s failed with %d %s in %s\n", \
75 func_name, tmp, strerror(tmp), _DBUS_FUNCTION_NAME); \
76 } \
77 } while (0)
78 #endif /* !DBUS_DISABLE_ASSERT */
79
80 static DBusMutex*
_dbus_pthread_mutex_new(void)81 _dbus_pthread_mutex_new (void)
82 {
83 DBusMutexPThread *pmutex;
84 int result;
85
86 pmutex = dbus_new (DBusMutexPThread, 1);
87 if (pmutex == NULL)
88 return NULL;
89
90 result = pthread_mutex_init (&pmutex->lock, NULL);
91
92 if (result == ENOMEM || result == EAGAIN)
93 {
94 dbus_free (pmutex);
95 return NULL;
96 }
97 else
98 {
99 PTHREAD_CHECK ("pthread_mutex_init", result);
100 }
101
102 /* Only written */
103 pmutex->count = 0;
104
105 /* There's no portable way to have a "null" pthread afaik so we
106 * can't set pmutex->holder to anything sensible. We only access it
107 * once the lock is held (which means we've set it).
108 */
109
110 return DBUS_MUTEX (pmutex);
111 }
112
113 static void
_dbus_pthread_mutex_free(DBusMutex * mutex)114 _dbus_pthread_mutex_free (DBusMutex *mutex)
115 {
116 DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex);
117
118 _dbus_assert (pmutex->count == 0);
119
120 PTHREAD_CHECK ("pthread_mutex_destroy", pthread_mutex_destroy (&pmutex->lock));
121
122 dbus_free (pmutex);
123 }
124
125 static void
_dbus_pthread_mutex_lock(DBusMutex * mutex)126 _dbus_pthread_mutex_lock (DBusMutex *mutex)
127 {
128 DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex);
129 pthread_t self = pthread_self ();
130
131 /* If the count is > 0 then someone had the lock, maybe us. If it is
132 * 0, then it might immediately change right after we read it,
133 * but it will be changed by another thread; i.e. if we read 0,
134 * we assume that this thread doesn't have the lock.
135 *
136 * Not 100% sure this is safe, but ... seems like it should be.
137 */
138 if (pmutex->count == 0)
139 {
140 /* We know we don't have the lock; someone may have the lock. */
141
142 PTHREAD_CHECK ("pthread_mutex_lock", pthread_mutex_lock (&pmutex->lock));
143
144 /* We now have the lock. Count must be 0 since it must be 0 when
145 * the lock is released by another thread, and we just now got
146 * the lock.
147 */
148 _dbus_assert (pmutex->count == 0);
149
150 pmutex->holder = self;
151 pmutex->count = 1;
152 }
153 else
154 {
155 /* We know someone had the lock, possibly us. Thus
156 * pmutex->holder is not pointing to junk, though it may not be
157 * the lock holder anymore if the lock holder is not us. If the
158 * lock holder is us, then we definitely have the lock.
159 */
160
161 if (pthread_equal (pmutex->holder, self))
162 {
163 /* We already have the lock. */
164 _dbus_assert (pmutex->count > 0);
165 }
166 else
167 {
168 /* Wait for the lock */
169 PTHREAD_CHECK ("pthread_mutex_lock", pthread_mutex_lock (&pmutex->lock));
170 pmutex->holder = self;
171 _dbus_assert (pmutex->count == 0);
172 }
173
174 pmutex->count += 1;
175 }
176 }
177
178 static void
_dbus_pthread_mutex_unlock(DBusMutex * mutex)179 _dbus_pthread_mutex_unlock (DBusMutex *mutex)
180 {
181 DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex);
182
183 _dbus_assert (pmutex->count > 0);
184
185 pmutex->count -= 1;
186
187 if (pmutex->count == 0)
188 PTHREAD_CHECK ("pthread_mutex_unlock", pthread_mutex_unlock (&pmutex->lock));
189
190 /* We leave pmutex->holder set to ourselves, its content is undefined if count is 0 */
191 }
192
193 static DBusCondVar *
_dbus_pthread_condvar_new(void)194 _dbus_pthread_condvar_new (void)
195 {
196 DBusCondVarPThread *pcond;
197 pthread_condattr_t attr;
198 int result;
199
200 pcond = dbus_new (DBusCondVarPThread, 1);
201 if (pcond == NULL)
202 return NULL;
203
204 pthread_condattr_init (&attr);
205 #ifdef HAVE_MONOTONIC_CLOCK
206 if (have_monotonic_clock)
207 pthread_condattr_setclock (&attr, CLOCK_MONOTONIC);
208 #endif
209
210 result = pthread_cond_init (&pcond->cond, &attr);
211 pthread_condattr_destroy (&attr);
212
213 if (result == EAGAIN || result == ENOMEM)
214 {
215 dbus_free (pcond);
216 return NULL;
217 }
218 else
219 {
220 PTHREAD_CHECK ("pthread_cond_init", result);
221 }
222
223 return DBUS_COND_VAR (pcond);
224 }
225
226 static void
_dbus_pthread_condvar_free(DBusCondVar * cond)227 _dbus_pthread_condvar_free (DBusCondVar *cond)
228 {
229 DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond);
230
231 PTHREAD_CHECK ("pthread_cond_destroy", pthread_cond_destroy (&pcond->cond));
232
233 dbus_free (pcond);
234 }
235
236 static void
_dbus_pthread_condvar_wait(DBusCondVar * cond,DBusMutex * mutex)237 _dbus_pthread_condvar_wait (DBusCondVar *cond,
238 DBusMutex *mutex)
239 {
240 DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex);
241 DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond);
242 int old_count;
243
244 _dbus_assert (pmutex->count > 0);
245 _dbus_assert (pthread_equal (pmutex->holder, pthread_self ()));
246
247 old_count = pmutex->count;
248 pmutex->count = 0; /* allow other threads to lock */
249 PTHREAD_CHECK ("pthread_cond_wait", pthread_cond_wait (&pcond->cond, &pmutex->lock));
250 _dbus_assert (pmutex->count == 0);
251 pmutex->holder = pthread_self(); /* other threads may have locked the mutex in the meantime */
252
253 /* The order of this line and the above line is important.
254 * See the comments below at the end of _dbus_pthread_condvar_wait_timeout
255 */
256 pmutex->count = old_count;
257 }
258
259 static dbus_bool_t
_dbus_pthread_condvar_wait_timeout(DBusCondVar * cond,DBusMutex * mutex,int timeout_milliseconds)260 _dbus_pthread_condvar_wait_timeout (DBusCondVar *cond,
261 DBusMutex *mutex,
262 int timeout_milliseconds)
263 {
264 DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex);
265 DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond);
266 struct timeval time_now;
267 struct timespec end_time;
268 int result;
269 int old_count;
270
271 _dbus_assert (pmutex->count > 0);
272 _dbus_assert (pthread_equal (pmutex->holder, pthread_self ()));
273
274 #ifdef HAVE_MONOTONIC_CLOCK
275 if (have_monotonic_clock)
276 {
277 struct timespec monotonic_timer;
278 clock_gettime (CLOCK_MONOTONIC,&monotonic_timer);
279 time_now.tv_sec = monotonic_timer.tv_sec;
280 time_now.tv_usec = monotonic_timer.tv_nsec / 1000;
281 }
282 else
283 /* This else falls through to gettimeofday */
284 #endif
285 gettimeofday (&time_now, NULL);
286
287 end_time.tv_sec = time_now.tv_sec + timeout_milliseconds / 1000;
288 end_time.tv_nsec = (time_now.tv_usec + (timeout_milliseconds % 1000) * 1000) * 1000;
289 if (end_time.tv_nsec > 1000*1000*1000)
290 {
291 end_time.tv_sec += 1;
292 end_time.tv_nsec -= 1000*1000*1000;
293 }
294
295 old_count = pmutex->count;
296 pmutex->count = 0;
297 result = pthread_cond_timedwait (&pcond->cond, &pmutex->lock, &end_time);
298
299 if (result != ETIMEDOUT)
300 {
301 PTHREAD_CHECK ("pthread_cond_timedwait", result);
302 }
303
304 _dbus_assert (pmutex->count == 0);
305 pmutex->holder = pthread_self(); /* other threads may have locked the mutex in the meantime */
306
307 /* restore to old count after setting the owner back to self,
308 * If reversing this line with above line, the previous owner thread could
309 * get into the mutex without proper locking by passing the lock owner check.
310 */
311 pmutex->count = old_count;
312
313 /* return true if we did not time out */
314 return result != ETIMEDOUT;
315 }
316
317 static void
_dbus_pthread_condvar_wake_one(DBusCondVar * cond)318 _dbus_pthread_condvar_wake_one (DBusCondVar *cond)
319 {
320 DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond);
321
322 PTHREAD_CHECK ("pthread_cond_signal", pthread_cond_signal (&pcond->cond));
323 }
324
325 static void
_dbus_pthread_condvar_wake_all(DBusCondVar * cond)326 _dbus_pthread_condvar_wake_all (DBusCondVar *cond)
327 {
328 DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond);
329
330 PTHREAD_CHECK ("pthread_cond_broadcast", pthread_cond_broadcast (&pcond->cond));
331 }
332
333 static const DBusThreadFunctions pthread_functions =
334 {
335 DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_NEW_MASK |
336 DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_FREE_MASK |
337 DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_LOCK_MASK |
338 DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_UNLOCK_MASK |
339 DBUS_THREAD_FUNCTIONS_CONDVAR_NEW_MASK |
340 DBUS_THREAD_FUNCTIONS_CONDVAR_FREE_MASK |
341 DBUS_THREAD_FUNCTIONS_CONDVAR_WAIT_MASK |
342 DBUS_THREAD_FUNCTIONS_CONDVAR_WAIT_TIMEOUT_MASK |
343 DBUS_THREAD_FUNCTIONS_CONDVAR_WAKE_ONE_MASK|
344 DBUS_THREAD_FUNCTIONS_CONDVAR_WAKE_ALL_MASK,
345 NULL, NULL, NULL, NULL,
346 _dbus_pthread_condvar_new,
347 _dbus_pthread_condvar_free,
348 _dbus_pthread_condvar_wait,
349 _dbus_pthread_condvar_wait_timeout,
350 _dbus_pthread_condvar_wake_one,
351 _dbus_pthread_condvar_wake_all,
352 _dbus_pthread_mutex_new,
353 _dbus_pthread_mutex_free,
354 _dbus_pthread_mutex_lock,
355 _dbus_pthread_mutex_unlock
356 };
357
358 static void
check_monotonic_clock(void)359 check_monotonic_clock (void)
360 {
361 #ifdef HAVE_MONOTONIC_CLOCK
362 struct timespec dummy;
363 if (clock_getres (CLOCK_MONOTONIC, &dummy) == 0)
364 have_monotonic_clock = TRUE;
365 #endif
366 }
367
368 dbus_bool_t
_dbus_threads_init_platform_specific(void)369 _dbus_threads_init_platform_specific (void)
370 {
371 check_monotonic_clock ();
372 return dbus_threads_init (&pthread_functions);
373 }
374