diff options
Diffstat (limited to 'condvar.c')
| -rw-r--r-- | condvar.c | 705 |
1 files changed, 705 insertions, 0 deletions
@@ -5,6 +5,709 @@ * This translation unit implements condition variables and their primitives. */ +/* + * Code contributed by John E. Bossom <JEB>. + */ + +#include <errno.h> +#include <string.h> + +#include "pthread.h" +#include "implement.h" + +int +pthread_condattr_init (pthread_condattr_t * attr) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * Initializes a condition variable attributes object + * with default attributes. + * + * PARAMETERS + * attr + * pointer to an instance of pthread_condattr_t + * + * + * DESCRIPTION + * Initializes a condition variable attributes object + * with default attributes. + * + * NOTES: + * 1) Use to define condition variable types + * 2) It is up to the application to ensure + * that it doesn't re-init an attribute + * without destroying it first. Otherwise + * a memory leak is created. + * + * RESULTS + * 0 successfully initialized attr, + * ENOMEM insufficient memory for attr. + * + * ------------------------------------------------------ + */ +{ + pthread_condattr_t attr_result; + int result = 0; + + attr_result = calloc (1, sizeof (*attr_result)); + + if (attr_result == NULL) + { + result = ENOMEM; + } + + *attr = attr_result; + + return (result); + +} /* pthread_condattr_init */ + + +int +pthread_condattr_destroy (pthread_condattr_t * attr) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * Destroys a condition variable attributes object. + * The object can no longer be used. + * + * PARAMETERS + * attr + * pointer to an instance of pthread_condattr_t + * + * + * DESCRIPTION + * Destroys a condition variable attributes object. + * The object can no longer be used. + * + * NOTES: + * 1) Does not affect condition variables created + * using 'attr' + * + * RESULTS + * 0 successfully released attr, + * EINVAL 'attr' is invalid. + * + * ------------------------------------------------------ + */ +{ + int result = 0; + + if (attr == NULL || *attr == NULL) + { + result = EINVAL; + + } + else + { + free (*attr); + + *attr = NULL; + result = 0; + } + + return (result); + +} /* pthread_condattr_destroy */ + + +int +pthread_condattr_getpshared (const pthread_condattr_t * attr, int *pshared) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * Determine whether condition variables created with 'attr' + * can be shared between processes. + * + * PARAMETERS + * attr + * pointer to an instance of pthread_condattr_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 + * Condition Variables created with 'attr' can be shared + * between processes if pthread_cond_t variable is allocated + * in memory shared by these processes. + * NOTES: + * 1) pshared condition variables 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_condattr_getpshared */ + + +int +pthread_condattr_setpshared (pthread_condattr_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_condattr_setpshared */ + + +int +pthread_cond_init (pthread_cond_t * cond, const pthread_condattr_t * attr) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function initializes a condition variable. + * + * PARAMETERS + * cond + * pointer to an instance of pthread_cond_t + * + * attr + * specifies optional creation attributes. + * + * + * DESCRIPTION + * This function initializes a condition variable. + * + * RESULTS + * 0 successfully created condition variable, + * EINVAL 'attr' is invalid, + * EAGAIN insufficient resources (other than + * memory, + * ENOMEM insufficient memory, + * EBUSY 'cond' is already initialized, + * + * ------------------------------------------------------ + */ +{ + int result = EAGAIN; + pthread_cond_t cv; + + if ((attr != NULL && *attr != NULL) && + ((*attr)->pshared == PTHREAD_PROCESS_SHARED)) + { + /* + * Creating condition variable that can be shared between + * processes. + */ + result = ENOSYS; + + goto FAIL0; + } + + cv = (pthread_cond_t) calloc (1, sizeof (*cv)); + + if (cv != NULL) + { + result = ENOMEM; + goto FAIL0; + } + + cv->waiters = 0; + cv->wasBroadcast = FALSE; + + if (sem_init (&(cv->sema), 0, 1) != 0) + { + goto FAIL0; + } + if (pthread_mutex_init (&(cv->waitersLock), NULL) != 0) + { + goto FAIL1; + } + + cv->waitersDone = CreateEvent ( + 0, + (int) FALSE, /* manualReset */ + (int) FALSE, /* setSignaled */ + NULL); + + if (cv->waitersDone == NULL) + { + goto FAIL2; + } + + result = 0; + + goto DONE; + + /* + * ------------- + * Failure Code + * ------------- + */ +FAIL2: + (void) pthread_mutex_destroy (&(cv->waitersLock)); + +FAIL1: + (void) sem_destroy (&(cv->sema)); + free (cv); + cv = NULL; + +FAIL0: +DONE: + *cond = cv; + return (result); + +} /* pthread_cond_init */ + + +int +pthread_cond_destroy (pthread_cond_t * cond) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function destroys a condition variable + * + * + * PARAMETERS + * cond + * pointer to an instance of pthread_cond_t + * + * + * DESCRIPTION + * This function destroys a condition variable. + * + * NOTES: + * 1) Safest after wakeup from 'cond', when + * no other threads will wait. + * + * RESULTS + * 0 successfully released condition variable, + * EINVAL 'cond' is invalid, + * EBUSY 'cond' is in use, + * + * ------------------------------------------------------ + */ +{ + int result = 0; + pthread_cond_t cv; + + if (cond != NULL && *cond != NULL) + { + cv = *cond; + + (void) sem_destroy (&(cv->sema)); + (void) pthread_mutex_destroy (&(cv->waitersLock)); + (void) CloseHandle (cv->waitersDone); + + free (cv); + + *cond = NULL; + } + + return (result); +} + +int +pthread_cond_wait (pthread_cond_t * cond, pthread_mutex_t * mutex) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function waits on a condition variable until + * awakened by a signal or broadcast. + * + * Caller MUST be holding the mutex lock; the + * lock is released and the caller is blocked waiting + * on 'cond'. When 'cond' is signaled, the mutex + * is re-acquired before returning to the caller. + * + * PARAMETERS + * cond + * pointer to an instance of pthread_cond_t + * + * mutex + * pointer to an instance of pthread_mutex_t + * + * + * DESCRIPTION + * This function waits on a condition variable until + * awakened by a signal or broadcast. + * + * NOTES: + * 1) The function must be called with 'mutex' LOCKED + * by the calling thread, or undefined behaviour + * will result. + * + * 2) This routine atomically releases 'mutex' and causes + * the calling thread to block on the condition variable. + * The blocked thread may be awakened by + * pthread_cond_signal or + * pthread_cond_broadcast. + * + * Upon successful completion, the 'mutex' has been locked and + * is owned by the calling thread. + * + * RESULTS + * 0 caught condition; mutex released, + * EINVAL 'cond' or 'mutex' is invalid, + * EINVAL different mutexes for concurrent waits, + * EINVAL mutex is not held by the calling thread, + * + * ------------------------------------------------------ + */ +{ + int result = 0; + pthread_cond_t cv; + int lastWaiter; + + cv = *cond; + + /* + * OK to increment cv->waiters because the caller locked 'mutex' + * + * FIXME: This is true. However, it is technically possible to call cond_wait + * on this cv with a different mutex. The standard leaves the result of such an + * action as undefined. (RPJ) + */ + cv->waiters++; + + /* + * We keep the lock held just long enough to increment the count of + * waiters by one (above). + * Note that we can't keep it held across the + * call to sem_wait since that will deadlock other calls + * to pthread_cond_signal + */ + if ((result = pthread_mutex_unlock (mutex)) == 0) + { + /* + * Wait to be awakened by + * pthread_cond_signal, or + * pthread_cond_broadcast + * + * Note: + * sem_wait is a cancellation point, hence providing the + * mechanism for making pthread_cond_wait a cancellation + * point. We use the cleanup mechanism to ensure we + * re-lock the mutex if we are cancelled. + */ + pthread_cleanup_push (pthread_mutex_lock, mutex); + + result = sem_wait (&(cv->sema)); + + pthread_cleanup_pop (0); + } + + if ((result = pthread_mutex_lock (&(cv->waitersLock))) == 0) + { + /* + * By making the waiter responsible for decrementing + * its count we don't have to worry about having an internal + * mutex. + */ + cv->waiters--; + + lastWaiter = cv->wasBroadcast && (cv->waiters == 0); + + result = pthread_mutex_unlock (&(cv->waitersLock)); + } + + if (result == 0) + { + if (lastWaiter) + { + /* + * If we are the last waiter on this broadcast + * let the thread doing the broadcast proceed + */ + if (!SetEvent (cv->waitersDone)) + { + result = EINVAL; + } + } + } + + /* + * We must always regain the external mutex, even when + * errors occur because that's the guarantee that we give + * to our callers + */ + (void) pthread_mutex_lock (mutex); + + + return (result); + +} /* pthread_cond_wait */ + + +int +pthread_cond_timedwait (pthread_cond_t * cond, + pthread_mutex_t * mutex, + const struct timespec *abstime) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function initializes an unnamed semaphore. the + * initial value of the semaphore is 'value' + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * + * DESCRIPTION + * This function initializes an unnamed semaphore. The + * initial value of the semaphore is set to 'value'. + * + * RESULTS + * 0 successfully created semaphore, + * EINVAL 'sem' is not a valid semaphore, + * ENOSPC a required resource has been exhausted, + * ENOSYS semaphores are not supported, + * EPERM the process lacks appropriate privilege + * + * ------------------------------------------------------ + */ +{ + int result = 0; + /* + * NOT IMPLEMENTED YET!!! + */ + return (result); +} + + +int +pthread_cond_signal (pthread_cond_t * cond) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function signals a condition variable, waking + * one waiting thread. + * If SCHED_FIFO or SCHED_RR policy threads are waiting + * the highest priority waiter is awakened; otherwise, + * an unspecified waiter is awakened. + * + * PARAMETERS + * cond + * pointer to an instance of pthread_cond_t + * + * + * DESCRIPTION + * This function signals a condition variable, waking + * one waiting thread. + * If SCHED_FIFO or SCHED_RR policy threads are waiting + * the highest priority waiter is awakened; otherwise, + * an unspecified waiter is awakened. + * + * NOTES: + * 1) Use when any waiter can respond and only one need + * respond (all waiters being equal). + * + * 2) This function MUST be called under the protection + * of the SAME mutex that is used with the condition + * variable being signaled; OTHERWISE, the condition + * variable may be signaled between the test of the + * associated condition and the blocking + * pthread_cond_signal. + * This can cause an infinite wait. + * + * RESULTS + * 0 successfully signaled condition, + * EINVAL 'cond' is invalid, + * + * ------------------------------------------------------ + */ +{ + int result = 0; + pthread_cond_t cv = *cond; + + /* + * If there aren't any waiters, then this is a no-op. + */ + if (cv->waiters > 0) + { + + result = sem_post (&(cv->sema)); + } + + return (result); + +} /* pthread_cond_signal */ + +int +pthread_cond_broadcast (pthread_cond_t * cond) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function broadcasts the condition variable, + * waking all current waiters. + * + * PARAMETERS + * sem + * pointer to an instance of pthread_cond_t + * + * + * DESCRIPTION + * This function initializes an unnamed semaphore. The + * initial value of the semaphore is set to 'value'. + * + * NOTES: + * 1) This function MUST be called under the protection + * of the SAME mutex that is used with the condition + * variable being signaled; OTHERWISE, the condition + * variable may be signaled between the test of the + * associated condition and the blocking pthread_cond_wait. + * This can cause an infinite wait. + * + * 2) Use when more than one waiter may respond to + * predicate change or if any waiting thread may + * not be able to respond + * + * RESULTS + * 0 successfully created semaphore, + * EINVAL 'cond' is invalid + * ENOSPC a required resource has been exhausted, + * + * ------------------------------------------------------ + */ +{ + int result = 0; + pthread_cond_t cv = *cond; + int i; + + cv->wasBroadcast = TRUE; + + /* + * Wake up all waiters + */ + for (i = cv->waiters; i > 0 && result == 0; i--) + { + + result = sem_post (&(cv->sema)); + } + + if (result == 0) + { + /* + * Wait for all the awakened threads to acquire their part of + * the counting semaphore + */ + if (WaitForSingleObject (cv->waitersDone, INFINITE) != + WAIT_OBJECT_0) + { + + result = 0; + + } + else + { + result = EINVAL; + } + + } + + return (result); +} + +/* </JEB> */ + + +#if 0 /* Pre Bossom */ + #include <errno.h> #include <windows.h> @@ -202,3 +905,5 @@ pthread_cond_destroy(pthread_cond_t *cv) return pthread_mutex_destroy(&cv->waiters_count_lock); } + +#endif /* Pre Bossom */ |