From f4423b3382dec90d4fe1abee445b495b7e8842a2 Mon Sep 17 00:00:00 2001 From: Simon McVittie Date: Tue, 14 Feb 2012 19:02:20 +0000 Subject: [PATCH 4/7] Use actual recursive pthreads mutexes, rather than NIH'ing them, wrong Very loosely based on a patch from Sigmund Augdal. For the moment, we make PTHREAD_MUTEX_RECURSIVE a hard requirement: it's required by POSIX 2008 Base and SUSv2. If your (non-Windows) platform doesn't have PTHREAD_MUTEX_RECURSIVE, please report a bug on freedesktop.org bugzilla with details of the platform in question. Bug: https://bugs.freedesktop.org/show_bug.cgi?id=43744 Signed-off-by: Simon McVittie --- dbus/dbus-sysdeps-pthread.c | 149 ++++++++++++++---------------------------- 1 files changed, 50 insertions(+), 99 deletions(-) diff --git a/dbus/dbus-sysdeps-pthread.c b/dbus/dbus-sysdeps-pthread.c index 7073751..062b53e 100644 --- a/dbus/dbus-sysdeps-pthread.c +++ b/dbus/dbus-sysdeps-pthread.c @@ -44,12 +44,7 @@ static dbus_bool_t have_monotonic_clock = 0; typedef struct { - pthread_mutex_t lock; /**< lock protecting count field */ - volatile int count; /**< count of how many times lock holder has recursively locked */ - volatile pthread_t holder; /**< holder of the lock if count >0, - valid but arbitrary thread if count - has ever been >0, uninitialized memory - if count has never been >0 */ + pthread_mutex_t lock; /**< the lock */ } DBusMutexPThread; typedef struct { @@ -77,12 +72,12 @@ typedef struct { } while (0) #endif /* !DBUS_DISABLE_ASSERT */ -static DBusMutex* -_dbus_pthread_mutex_new (void) +static DBusMutex * +_dbus_pthread_cmutex_new (void) { DBusMutexPThread *pmutex; int result; - + pmutex = dbus_new (DBusMutexPThread, 1); if (pmutex == NULL) return NULL; @@ -99,14 +94,35 @@ _dbus_pthread_mutex_new (void) PTHREAD_CHECK ("pthread_mutex_init", result); } - /* Only written */ - pmutex->count = 0; + return DBUS_MUTEX (pmutex); +} + +static DBusMutex * +_dbus_pthread_rmutex_new (void) +{ + DBusMutexPThread *pmutex; + pthread_mutexattr_t mutexattr; + int result; + + pmutex = dbus_new (DBusMutexPThread, 1); + if (pmutex == NULL) + return NULL; + + pthread_mutexattr_init (&mutexattr); + pthread_mutexattr_settype (&mutexattr, PTHREAD_MUTEX_RECURSIVE); + result = pthread_mutex_init (&pmutex->lock, &mutexattr); + pthread_mutexattr_destroy (&mutexattr); + + if (result == ENOMEM || result == EAGAIN) + { + dbus_free (pmutex); + return NULL; + } + else + { + PTHREAD_CHECK ("pthread_mutex_init", result); + } - /* There's no portable way to have a "null" pthread afaik so we - * can't set pmutex->holder to anything sensible. We only access it - * once the lock is held (which means we've set it). - */ - return DBUS_MUTEX (pmutex); } @@ -115,79 +131,26 @@ _dbus_pthread_mutex_free (DBusMutex *mutex) { DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex); - _dbus_assert (pmutex->count == 0); - PTHREAD_CHECK ("pthread_mutex_destroy", pthread_mutex_destroy (&pmutex->lock)); - dbus_free (pmutex); } -static void +static dbus_bool_t _dbus_pthread_mutex_lock (DBusMutex *mutex) { DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex); - pthread_t self = pthread_self (); - - /* If the count is > 0 then someone had the lock, maybe us. If it is - * 0, then it might immediately change right after we read it, - * but it will be changed by another thread; i.e. if we read 0, - * we assume that this thread doesn't have the lock. - * - * Not 100% sure this is safe, but ... seems like it should be. - */ - if (pmutex->count == 0) - { - /* We know we don't have the lock; someone may have the lock. */ - - PTHREAD_CHECK ("pthread_mutex_lock", pthread_mutex_lock (&pmutex->lock)); - - /* We now have the lock. Count must be 0 since it must be 0 when - * the lock is released by another thread, and we just now got - * the lock. - */ - _dbus_assert (pmutex->count == 0); - - pmutex->holder = self; - pmutex->count = 1; - } - else - { - /* We know someone had the lock, possibly us. Thus - * pmutex->holder is not pointing to junk, though it may not be - * the lock holder anymore if the lock holder is not us. If the - * lock holder is us, then we definitely have the lock. - */ - - if (pthread_equal (pmutex->holder, self)) - { - /* We already have the lock. */ - _dbus_assert (pmutex->count > 0); - } - else - { - /* Wait for the lock */ - PTHREAD_CHECK ("pthread_mutex_lock", pthread_mutex_lock (&pmutex->lock)); - pmutex->holder = self; - _dbus_assert (pmutex->count == 0); - } - - pmutex->count += 1; - } + + PTHREAD_CHECK ("pthread_mutex_lock", pthread_mutex_lock (&pmutex->lock)); + return TRUE; } -static void +static dbus_bool_t _dbus_pthread_mutex_unlock (DBusMutex *mutex) { DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex); - _dbus_assert (pmutex->count > 0); - - pmutex->count -= 1; - - if (pmutex->count == 0) - PTHREAD_CHECK ("pthread_mutex_unlock", pthread_mutex_unlock (&pmutex->lock)); - - /* We leave pmutex->holder set to ourselves, its content is undefined if count is 0 */ + PTHREAD_CHECK ("pthread_mutex_unlock", pthread_mutex_unlock (&pmutex->lock)); + return TRUE; } static DBusCondVar * @@ -239,17 +202,8 @@ _dbus_pthread_condvar_wait (DBusCondVar *cond, { DBusMutexPThread *pmutex = DBUS_MUTEX_PTHREAD (mutex); DBusCondVarPThread *pcond = DBUS_COND_VAR_PTHREAD (cond); - int old_count; - - _dbus_assert (pmutex->count > 0); - _dbus_assert (pthread_equal (pmutex->holder, pthread_self ())); - old_count = pmutex->count; - pmutex->count = 0; /* allow other threads to lock */ PTHREAD_CHECK ("pthread_cond_wait", pthread_cond_wait (&pcond->cond, &pmutex->lock)); - _dbus_assert (pmutex->count == 0); - pmutex->count = old_count; - pmutex->holder = pthread_self(); /* other threads may have locked the mutex in the meantime */ } static dbus_bool_t @@ -262,10 +216,6 @@ _dbus_pthread_condvar_wait_timeout (DBusCondVar *cond, struct timeval time_now; struct timespec end_time; int result; - int old_count; - - _dbus_assert (pmutex->count > 0); - _dbus_assert (pthread_equal (pmutex->holder, pthread_self ())); #ifdef HAVE_MONOTONIC_CLOCK if (have_monotonic_clock) @@ -288,8 +238,6 @@ _dbus_pthread_condvar_wait_timeout (DBusCondVar *cond, end_time.tv_nsec -= 1000*1000*1000; } - old_count = pmutex->count; - pmutex->count = 0; result = pthread_cond_timedwait (&pcond->cond, &pmutex->lock, &end_time); if (result != ETIMEDOUT) @@ -297,10 +245,6 @@ _dbus_pthread_condvar_wait_timeout (DBusCondVar *cond, PTHREAD_CHECK ("pthread_cond_timedwait", result); } - _dbus_assert (pmutex->count == 0); - pmutex->count = old_count; - pmutex->holder = pthread_self(); /* other threads may have locked the mutex in the meantime */ - /* return true if we did not time out */ return result != ETIMEDOUT; } @@ -323,6 +267,10 @@ _dbus_pthread_condvar_wake_all (DBusCondVar *cond) static const DBusThreadFunctions pthread_functions = { + DBUS_THREAD_FUNCTIONS_MUTEX_NEW_MASK | + DBUS_THREAD_FUNCTIONS_MUTEX_FREE_MASK | + DBUS_THREAD_FUNCTIONS_MUTEX_LOCK_MASK | + DBUS_THREAD_FUNCTIONS_MUTEX_UNLOCK_MASK | DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_NEW_MASK | DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_FREE_MASK | DBUS_THREAD_FUNCTIONS_RECURSIVE_MUTEX_LOCK_MASK | @@ -333,17 +281,20 @@ static const DBusThreadFunctions pthread_functions = DBUS_THREAD_FUNCTIONS_CONDVAR_WAIT_TIMEOUT_MASK | DBUS_THREAD_FUNCTIONS_CONDVAR_WAKE_ONE_MASK| DBUS_THREAD_FUNCTIONS_CONDVAR_WAKE_ALL_MASK, - NULL, NULL, NULL, NULL, + _dbus_pthread_cmutex_new, + _dbus_pthread_mutex_free, + _dbus_pthread_mutex_lock, + _dbus_pthread_mutex_unlock, _dbus_pthread_condvar_new, _dbus_pthread_condvar_free, _dbus_pthread_condvar_wait, _dbus_pthread_condvar_wait_timeout, _dbus_pthread_condvar_wake_one, _dbus_pthread_condvar_wake_all, - _dbus_pthread_mutex_new, + _dbus_pthread_rmutex_new, _dbus_pthread_mutex_free, - _dbus_pthread_mutex_lock, - _dbus_pthread_mutex_unlock + (void (*) (DBusMutex *)) _dbus_pthread_mutex_lock, + (void (*) (DBusMutex *)) _dbus_pthread_mutex_unlock }; static void -- 1.7.9