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 */
44static dbus_bool_t have_monotonic_clock = 0;
45
46typedef 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
55typedef 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
80static DBusMutex*
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
113static void
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
125static void
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
178static void
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
193static DBusCondVar *
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
226static void
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
236static void
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
259static dbus_bool_t
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
317static void
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
325static void
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
333static 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
358static void
359check_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
368dbus_bool_t
369_dbus_threads_init_platform_specific (void)
370{
371  check_monotonic_clock ();
372  return dbus_threads_init (&pthread_functions);
373}
374