/* * mutex.c * * Description: * This translation unit implements mutual exclusion (mutex) primitives. * * Pthreads-win32 - POSIX Threads Library for Win32 * Copyright (C) 1998 * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Library General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Library General Public License for more details. * * You should have received a copy of the GNU Library General Public * License along with this library; if not, write to the Free * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, * MA 02111-1307, USA */ /* errno.h or a replacement file is included by pthread.h */ //#include #include "pthread.h" #include "implement.h" static int ptw32_mutex_check_need_init(pthread_mutex_t *mutex) { int result = 0; /* * The following guarded test is specifically for statically * initialised mutexes (via PTHREAD_MUTEX_INITIALIZER). * * Note that by not providing this synchronisation we risk * introducing race conditions into applications which are * correctly written. * * Approach * -------- * We know that static mutexes will not be PROCESS_SHARED * so we can serialise access to internal state using * Win32 Critical Sections rather than Win32 Mutexes. * * If using a single global lock slows applications down too much, * multiple global locks could be created and hashed on some random * value associated with each mutex, the pointer perhaps. At a guess, * a good value for the optimal number of global locks might be * the number of processors + 1. * */ EnterCriticalSection(&ptw32_mutex_test_init_lock); /* * We got here possibly under race * conditions. Check again inside the critical section * and only initialise if the mutex is valid (not been destroyed). * If a static mutex has been destroyed, the application can * re-initialise it only by calling pthread_mutex_init() * explicitly. */ if (*mutex == (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT) { result = pthread_mutex_init(mutex, NULL); } else if (*mutex == NULL) { /* * The mutex has been destroyed while we were waiting to * initialise it, so the operation that caused the * auto-initialisation should fail. */ result = EINVAL; } LeaveCriticalSection(&ptw32_mutex_test_init_lock); return result; } int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr) /* * ------------------------------------------------------ * DOCPUBLIC * Initializes a mutex object with supplied or * default attributes. * * PARAMETERS * mutex * pointer to an instance of pthread_mutex_t * attr * pointer to an instance of pthread_mutexattr_t * * * DESCRIPTION * Initializes a mutex object with supplied or * default attributes. * * RESULTS * 0 successfully initialized attr, * EINVAL not a valid mutex pointer, * ENOMEM insufficient memory for attr, * ENOSYS one or more requested attributes * are not supported. * * ------------------------------------------------------ */ { int result = 0; pthread_mutex_t mx; if (mutex == NULL) { return EINVAL; } mx = (pthread_mutex_t) calloc(1, sizeof(*mx)); if (mx == NULL) { result = ENOMEM; goto FAIL0; } mx->lock_idx = -1; mx->try_lock = 0; mx->owner = NULL; mx->waiters = 0; mx->lastOwner = NULL; mx->lastWaiter = NULL; if (attr != NULL && *attr != NULL) { mx->type = (*attr)->type; mx->pshared = (*attr)->pshared; if (mx->pshared == PTHREAD_PROCESS_SHARED) { /* * Creating mutex that can be shared between * processes. */ #if _POSIX_THREAD_PROCESS_SHARED /* * Not implemented yet. */ #error ERROR [__FILE__, line __LINE__]: Process shared mutexes are not supported yet. #else result = ENOSYS; #endif /* _POSIX_THREAD_PROCESS_SHARED */ } } else { mx->type = PTHREAD_MUTEX_DEFAULT; mx->pshared = PTHREAD_PROCESS_PRIVATE; } if (mx->type == PTHREAD_MUTEX_DEFAULT) { mx->type = ptw32_mutex_mapped_default; } if (result != 0 && mx != NULL) { free(mx); mx = NULL; } FAIL0: *mutex = mx; return(result); } int pthread_mutex_destroy(pthread_mutex_t *mutex) /* * ------------------------------------------------------ * DOCPUBLIC * Destroys a mutex object and returns any resources * to the system. * * PARAMETERS * mutex * pointer to an instance of pthread_mutex_t * * DESCRIPTION * Destroys a mutex object and returns any resources * to the system. * * RESULTS * 0 successfully initialized attr, * EINVAL not a valid mutex pointer, * EBUSY the mutex is currently locked. * * ------------------------------------------------------ */ { int result = 0; pthread_mutex_t mx; if (mutex == NULL || *mutex == NULL) { return EINVAL; } /* * Check to see if we have something to delete. */ if (*mutex != (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT) { mx = *mutex; /* * Check to see if the mutex is held by any thread. We * can't destroy it if it is. Pthread_mutex_trylock is * not recursive and will return EBUSY even if the current * thread holds the lock. */ result = pthread_mutex_trylock(&mx); if (result == 0) { /* * FIXME!!! * The mutex isn't held by another thread but we could still * be too late invalidating the mutex below. Yet we can't do it * earlier in case another thread needs to unlock the mutex * that it's holding. */ *mutex = NULL; result = pthread_mutex_unlock(&mx); if (result == 0) { free(mx); } else { /* * Restore the mutex before we return the error. */ *mutex = mx; } } } else { /* * See notes in ptw32_mutex_check_need_init() above also. */ EnterCriticalSection(&ptw32_mutex_test_init_lock); /* * Check again. */ if (*mutex == (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT) { /* * This is all we need to do to destroy a statically * initialised mutex that has not yet been used (initialised). * If we get to here, another thread * waiting to initialise this mutex will get an EINVAL. */ *mutex = NULL; } else { if (*mutex == NULL) { /* * The mutex has been destroyed while we were waiting * so we just ignore it. */ } else { /* * The mutex has been initialised while we were waiting * so assume it's in use. */ result = EBUSY; } } LeaveCriticalSection(&ptw32_mutex_test_init_lock); } return result; } int pthread_mutexattr_init (pthread_mutexattr_t * attr) /* * ------------------------------------------------------ * DOCPUBLIC * Initializes a mutex attributes object with default * attributes. * * PARAMETERS * attr * pointer to an instance of pthread_mutexattr_t * * * DESCRIPTION * Initializes a mutex attributes object with default * attributes. * * NOTES: * 1) Used to define mutex types * * RESULTS * 0 successfully initialized attr, * ENOMEM insufficient memory for attr. * * ------------------------------------------------------ */ { pthread_mutexattr_t ma; int result = 0; ma = (pthread_mutexattr_t) calloc (1, sizeof (*ma)); if (ma == NULL) { result = ENOMEM; } ma->pshared = PTHREAD_PROCESS_PRIVATE; ma->type = PTHREAD_MUTEX_DEFAULT; *attr = ma; return (result); } /* pthread_mutexattr_init */ int pthread_mutexattr_destroy (pthread_mutexattr_t * attr) /* * ------------------------------------------------------ * DOCPUBLIC * Destroys a mutex attributes object. The object can * no longer be used. * * PARAMETERS * attr * pointer to an instance of pthread_mutexattr_t * * * DESCRIPTION * Destroys a mutex attributes object. The object can * no longer be used. * * NOTES: * 1) Does not affect mutexes created using 'attr' * * RESULTS * 0 successfully released attr, * EINVAL 'attr' is invalid. * * ------------------------------------------------------ */ { int result = 0; if (attr == NULL || *attr == NULL) { result = EINVAL; } else { pthread_mutexattr_t ma = *attr; *attr = NULL; free (ma); result = 0; } return (result); } /* pthread_mutexattr_destroy */ int pthread_mutexattr_getpshared (const pthread_mutexattr_t * attr, int *pshared) /* * ------------------------------------------------------ * DOCPUBLIC * Determine whether mutexes created with 'attr' can be * shared between processes. * * PARAMETERS * attr * pointer to an instance of pthread_mutexattr_t * * pshared * will be set to one of: * * PTHREAD_PROCESS_SHARED * May be shared if in shared memory * * PTHREAD_PROCESS_PRIVATE * Cannot be shared. * * * DESCRIPTION * Mutexes creatd with 'attr' can be shared between * processes if pthread_mutex_t variable is allocated * in memory shared by these processes. * NOTES: * 1) pshared mutexes MUST be allocated in shared * memory. * 2) The following macro is defined if shared mutexes * are supported: * _POSIX_THREAD_PROCESS_SHARED * * RESULTS * 0 successfully retrieved attribute, * EINVAL 'attr' is invalid, * * ------------------------------------------------------ */ { int result; if ((attr != NULL && *attr != NULL) && (pshared != NULL)) { *pshared = (*attr)->pshared; result = 0; } else { *pshared = PTHREAD_PROCESS_PRIVATE; result = EINVAL; } return (result); } /* pthread_mutexattr_getpshared */ int pthread_mutexattr_setpshared (pthread_mutexattr_t * attr, int pshared) /* * ------------------------------------------------------ * DOCPUBLIC * Mutexes created with 'attr' can be shared between * processes if pthread_mutex_t variable is allocated * in memory shared by these processes. * * PARAMETERS * attr * pointer to an instance of pthread_mutexattr_t * * pshared * must be one of: * * PTHREAD_PROCESS_SHARED * May be shared if in shared memory * * PTHREAD_PROCESS_PRIVATE * Cannot be shared. * * DESCRIPTION * Mutexes creatd with 'attr' can be shared between * processes if pthread_mutex_t variable is allocated * in memory shared by these processes. * * NOTES: * 1) pshared mutexes MUST be allocated in shared * memory. * * 2) The following macro is defined if shared mutexes * are supported: * _POSIX_THREAD_PROCESS_SHARED * * RESULTS * 0 successfully set attribute, * EINVAL 'attr' or pshared is invalid, * ENOSYS PTHREAD_PROCESS_SHARED not supported, * * ------------------------------------------------------ */ { int result; if ((attr != NULL && *attr != NULL) && ((pshared == PTHREAD_PROCESS_SHARED) || (pshared == PTHREAD_PROCESS_PRIVATE))) { if (pshared == PTHREAD_PROCESS_SHARED) { #if !defined( _POSIX_THREAD_PROCESS_SHARED ) result = ENOSYS; pshared = PTHREAD_PROCESS_PRIVATE; #else result = 0; #endif /* _POSIX_THREAD_PROCESS_SHARED */ } else { result = 0; } (*attr)->pshared = pshared; } else { result = EINVAL; } return (result); } /* pthread_mutexattr_setpshared */ int pthread_mutexattr_settype (pthread_mutexattr_t * attr, int type) /* * ------------------------------------------------------ * * DOCPUBLIC * The pthread_mutexattr_settype() and * pthread_mutexattr_gettype() functions respectively set and * get the mutex type attribute. This attribute is set in the * type parameter to these functions. * * PARAMETERS * attr * pointer to an instance of pthread_mutexattr_t * * type * must be one of: * * PTHREAD_MUTEX_DEFAULT * * PTHREAD_MUTEX_NORMAL * * PTHREAD_MUTEX_ERRORCHECK * * PTHREAD_MUTEX_RECURSIVE * * DESCRIPTION * The pthread_mutexattr_settype() and * pthread_mutexattr_gettype() functions respectively set and * get the mutex type attribute. This attribute is set in the * type parameter to these functions. The default value of the * type attribute is PTHREAD_MUTEX_DEFAULT. * * The type of mutex is contained in the type attribute of the * mutex attributes. Valid mutex types include: * * PTHREAD_MUTEX_NORMAL * This type of mutex does not detect deadlock. A * thread attempting to relock this mutex without * first unlocking it will deadlock. Attempting to * unlock a mutex locked by a different thread * results in undefined behavior. Attempting to * unlock an unlocked mutex results in undefined * behavior. * * PTHREAD_MUTEX_ERRORCHECK * This type of mutex provides error checking. A * thread attempting to relock this mutex without * first unlocking it will return with an error. A * thread attempting to unlock a mutex which another * thread has locked will return with an error. A * thread attempting to unlock an unlocked mutex will * return with an error. * * PTHREAD_MUTEX_DEFAULT * Same as PTHREAD_MUTEX_RECURSIVE. * * PTHREAD_MUTEX_RECURSIVE * A thread attempting to relock this mutex without * first unlocking it will succeed in locking the * mutex. The relocking deadlock which can occur with * mutexes of type PTHREAD_MUTEX_NORMAL cannot occur * with this type of mutex. Multiple locks of this * mutex require the same number of unlocks to * release the mutex before another thread can * acquire the mutex. A thread attempting to unlock a * mutex which another thread has locked will return * with an error. A thread attempting to unlock an * unlocked mutex will return with an error. This * type of mutex is only supported for mutexes whose * process shared attribute is * PTHREAD_PROCESS_PRIVATE. * * RESULTS * 0 successfully set attribute, * EINVAL 'attr' or 'type' is invalid, * * ------------------------------------------------------ */ { int result = 0; if ((attr != NULL && *attr != NULL)) { switch (type) { case PTHREAD_MUTEX_DEFAULT: case PTHREAD_MUTEX_NORMAL: case PTHREAD_MUTEX_ERRORCHECK: case PTHREAD_MUTEX_RECURSIVE: (*attr)->type = type; break; default: result = EINVAL; break; } } else { result = EINVAL; } return (result); } /* pthread_mutexattr_settype */ int pthread_mutexattr_gettype (pthread_mutexattr_t * attr, int * type) { int result = 0; if ((attr != NULL && *attr != NULL)) { *type = (*attr)->type; } else { result = EINVAL; } return (result); } int pthread_mutex_lock(pthread_mutex_t *mutex) /* * ------------------------------------------------------ * DOCPUBLIC * Locks an unlocked mutex. If the mutex is already * locked, the calling thread usually blocks, but * depending on the current owner and type of the mutex * may recursively lock the mutex or return an error. * * PARAMETERS * mutex * pointer to an instance of pthread_mutex_t * * DESCRIPTION * Locks an unlocked mutex. If the mutex is already * locked, the calling thread usually blocks, but * depending on the current owner and type of the mutex * may recursively lock the mutex or return an error. * * See the description under pthread_mutexattr_settype() * for details. * * RESULTS * 0 successfully locked mutex, * EINVAL not a valid mutex pointer, * ENOMEM insufficient memory to initialise * the statically declared mutex object, * EDEADLK the mutex is of type * PTHREAD_MUTEX_ERRORCHECK and the * calling thread already owns the mutex. * * ------------------------------------------------------ */ { int result = 0; pthread_mutex_t mx; if (mutex == NULL || *mutex == NULL) { return EINVAL; } /* * We do a quick check to see if we need to do more work * to initialise a static mutex. We check * again inside the guarded section of ptw32_mutex_check_need_init() * to avoid race conditions. */ if (*mutex == (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT) { result = ptw32_mutex_check_need_init(mutex); } if (result == 0) { pthread_t self = pthread_self(); mx = *mutex; switch (mx->type) { case PTHREAD_MUTEX_DEFAULT: case PTHREAD_MUTEX_RECURSIVE: while (TRUE) { if (0 == InterlockedIncrement(&mx->lock_idx)) { /* * Ensure that we give other waiting threads a * chance to take the mutex if we held it last time. */ if (InterlockedIncrement(&mx->waiters) > 0 && mx->lastOwner == self) { /* * Check to see if other waiting threads * have stopped waiting but haven't decremented * the 'waiters' counter - ie. they may have been * canceled. If we're wrong then waiting threads will * increment the value again. */ if (mx->lastWaiter == self) { (void) InterlockedExchange(&mx->waiters, 0L); } else { goto WAIT_RECURSIVE; } } LOCK_RECURSIVE: /* * Take the lock. */ mx->owner = self; mx->lastOwner = self; mx->lastWaiter = NULL; break; } else { while (mx->try_lock) { Sleep(0); } if (mx->owner == self) { goto LOCK_RECURSIVE; } WAIT_RECURSIVE: InterlockedIncrement(&mx->waiters); mx->lastWaiter = self; InterlockedDecrement(&mx->lock_idx); Sleep(0); /* * Thread priorities may have tricked another * thread into thinking we weren't waiting anymore. * If so, waiters will equal 0 so set it to 1 * before we decrement it. */ if (InterlockedDecrement(&mx->waiters) < 0) { InterlockedExchange(&mx->waiters, 0); } } } break; case PTHREAD_MUTEX_NORMAL: /* * If the thread already owns the mutex * then the thread will become deadlocked. */ while (TRUE) { if (0 == InterlockedIncrement(&mx->lock_idx)) { /* * Ensure that we give other waiting threads a * chance to take the mutex if we held it last time. */ if (InterlockedIncrement(&mx->waiters) > 0 && mx->lastOwner == self) { /* * Check to see if other waiting threads * have stopped waiting but haven't decremented * the 'waiters' counter - ie. they may have been * canceled. */ if (mx->lastWaiter == self) { InterlockedExchange(&mx->waiters, 0L); } else { goto WAIT_NORMAL; } } /* * Take the lock. */ mx->owner = self; mx->lastOwner = self; mx->lastWaiter = NULL; break; } else { while (mx->try_lock) { Sleep(0); } WAIT_NORMAL: InterlockedIncrement(&mx->waiters); mx->lastWaiter = self; InterlockedDecrement(&mx->lock_idx); Sleep(0); /* * Thread priorities may have tricked another * thread into thinking we weren't waiting anymore. * If so, waiters will equal 0 so set it to 1 * before we decrement it. */ if (InterlockedDecrement(&mx->waiters) < 0) { InterlockedExchange(&mx->waiters, 0); } } } break; case PTHREAD_MUTEX_ERRORCHECK: while (TRUE) { if (0 == InterlockedIncrement(&mx->lock_idx)) { /* * Ensure that we give other waiting threads a * chance to take the mutex if we held it last time. */ if (InterlockedIncrement(&mx->waiters) > 0 && mx->lastOwner == self) { /* * Check to see if other waiting threads * have stopped waiting but haven't decremented * the 'waiters' counter - ie. they may have been * canceled. */ if (mx->lastWaiter == self) { InterlockedExchange(&mx->waiters, 0L); } else { goto WAIT_ERRORCHECK; } } /* * Take the lock. */ mx->owner = self; mx->lastOwner = self; mx->lastWaiter = NULL; break; } else { while (mx->try_lock) { Sleep(0); } if (mx->owner == self) { result = EDEADLK; break; } WAIT_ERRORCHECK: InterlockedIncrement(&mx->waiters); mx->lastWaiter = self; InterlockedDecrement(&mx->lock_idx); Sleep(0); /* * Thread priorities may have tricked another * thread into thinking we weren't waiting anymore. * If so, waiters will equal 0 so set it to 1 * before we decrement it. */ if (InterlockedDecrement(&mx->waiters) < 0) { InterlockedExchange(&mx->waiters, 0); } } } break; default: result = EINVAL; break; } } return result; } int pthread_mutex_unlock(pthread_mutex_t *mutex) /* * ------------------------------------------------------ * DOCPUBLIC * Decrements the lock count of the currently locked mutex. * * PARAMETERS * mutex * pointer to an instance of pthread_mutex_t * * DESCRIPTION * Decrements the lock count of the currently locked mutex. * * If the count reaches it's 'unlocked' value then it * is available to be locked by another waiting thread. * The implementation ensures that other waiting threads * get a chance to take the unlocked mutex before the unlocking * thread can re-lock it. * * RESULTS * 0 successfully locked mutex, * EINVAL not a valid mutex pointer, * EPERM the current thread does not own * the mutex. * * ------------------------------------------------------ */ { int result = 0; pthread_mutex_t mx; if (mutex == NULL || *mutex == NULL) { return EINVAL; } mx = *mutex; /* * If the thread calling us holds the mutex then there is no * race condition. If another thread holds the * lock then we shouldn't be in here. */ if (mx != (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT && mx->owner == pthread_self()) { switch (mx->type) { case PTHREAD_MUTEX_NORMAL: case PTHREAD_MUTEX_ERRORCHECK: mx->owner = NULL; break; case PTHREAD_MUTEX_RECURSIVE: default: if (mx->lock_idx == 0) { mx->owner = NULL; } break; } InterlockedDecrement(&mx->lock_idx); } else { result = EPERM; } return result; } int pthread_mutex_trylock(pthread_mutex_t *mutex) /* * ------------------------------------------------------ * DOCPUBLIC * Tries to lock a mutex. If the mutex is already * locked (by any thread, including the calling thread), * the calling thread returns without waiting * for the mutex to be freed (nor recursively locking * the mutex if the calling thread currently owns it). * * PARAMETERS * mutex * pointer to an instance of pthread_mutex_t * * DESCRIPTION * Tries to lock a mutex. If the mutex is already * locked (by any thread, including the calling thread), * the calling thread returns without waiting * for the mutex to be freed (nor recursively locking * the mutex if the calling thread currently owns it). * * RESULTS * 0 successfully locked the mutex, * EINVAL not a valid mutex pointer, * EBUSY the mutex is currently locked, * ENOMEM insufficient memory to initialise * the statically declared mutex object. * * ------------------------------------------------------ */ { int result = 0; pthread_mutex_t mx; pthread_t self; if (mutex == NULL || *mutex == NULL) { return EINVAL; } /* * We do a quick check to see if we need to do more work * to initialise a static mutex. We check * again inside the guarded section of ptw32_mutex_check_need_init() * to avoid race conditions. */ if (*mutex == (pthread_mutex_t) PTW32_OBJECT_AUTO_INIT) { result = ptw32_mutex_check_need_init(mutex); } mx = *mutex; if (result == 0) { self = pthread_self(); /* * Trylock returns EBUSY if the mutex is held already, * even if the current thread owns the mutex - ie. it * doesn't lock it recursively, even * if the mutex type is PTHREAD_MUTEX_RECURSIVE. */ if (0 == (mx->lock_idx + 1)) { mx->try_lock++; if (0 == InterlockedIncrement(&mx->lock_idx)) { mx->owner = self; mx->lastOwner = self; mx->lastWaiter = NULL; } else { InterlockedDecrement(&mx->lock_idx); result = EBUSY; } mx->try_lock--; } else { result = EBUSY; } } return result; }