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Diffstat (limited to 'semaphore.c')
| -rw-r--r-- | semaphore.c | 254 |
1 files changed, 254 insertions, 0 deletions
diff --git a/semaphore.c b/semaphore.c new file mode 100644 index 0000000..c163336 --- /dev/null +++ b/semaphore.c @@ -0,0 +1,254 @@ +/* + * ------------------------------------------------------------- + * + * Module: semaphore.c + * + * Purpose: + * Semaphores aren't actually part of the PThreads standard. + * They are defined by the POSIX Standard: + * + * POSIX 1003.1b-1993 (POSIX.1b) + * + * They are supposed to follow the older UNIX convention for + * reporting errors. That is, on failure they are supposed + * to return a value of -1 and store the appropriate error + * number into 'errno'. + * HOWEVER,errno cannot be modified in a multithreaded + * program on WIN32; therefore, the value is returned as + * the function value. + * It is recommended that you compare for zero (0) for success + * instead of -1 for failure when checking the status of + * these functions. + * + * Contents: + * Public Methods Author + * -------------- ------ + * sem_init John E. Bossom Mar 1998 + * sem_destroy John E. Bossom Mar 1998 + * sem_trywait John E. Bossom Mar 1998 + * sem_wait John E. Bossom Mar 1998 + * sem_post John E. Bossom Mar 1998 + * + * Private Methods + * --------------- + * + * ------------------------------------------------------------- + */ +#include <pthread.h> +#include <windows.h> +#include <process.h> +#include <errno.h> +#include <string.h> + +#include "semaphore.h" + + +int +sem_init (sem_t * sem, int pshared, unsigned int value) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function initializes an unnamed semaphore. the + * initial value of the semaphore is 'value' + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * pshared + * if zero, this semaphore may only be shared between + * threads in the same process. + * if nonzero, the semaphore can be shared between + * processes + * + * value + * initial value of the semaphore counter + * + * 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; + + if (pshared != 0) + { + /* + * Creating a semaphore that can be shared between + * processes + */ + result = EPERM; + + } + else + { + /* + * NOTE: Taking advantage of the fact that + * sem_t is a simple structure with one entry; + * We don't have to allocate it... + */ + *sem = CreateSemaphore ( + 0, + value, + 0x7FFFFFF, + NULL); + + if (*sem == 0) + { + result = ENOSPC; + } + } + + return (result); + +} /* sem_init */ + + +int +sem_destroy (sem_t * sem) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function destroys an unnamed semaphore. + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * DESCRIPTION + * This function destroys an unnamed semaphore. + * + * RESULTS + * 0 successfully destroyed semaphore, + * EINVAL 'sem' is not a valid semaphore, + * ENOSYS semaphores are not supported, + * EBUSY threads (or processes) are currently + * blocked on 'sem' + * + * ------------------------------------------------------ + */ +{ + return ((sem == NULL) + ? EINVAL + : (CloseHandle (*sem) + ? 0 + : EINVAL)); + +} /* sem_destroy */ + + +int +sem_trywait (sem_t * sem) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function tries to wait on a semaphore. + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * DESCRIPTION + * This function tries to wait on a semaphore. If the + * semaphore value is greater than zero, it decreases + * its value by one. If the semaphore value is zero, then + * this function returns immediately with the error EAGAIN + * + * RESULTS + * 0 successfully destroyed semaphore, + * EAGAIN the semaphore was already locked, + * EINVAL 'sem' is not a valid semaphore, + * ENOSYS semaphores are not supported, + * EINTR the function was interrupted by a signal, + * EDEADLK a deadlock condition was detected. + * + * ------------------------------------------------------ + */ +{ + return ((sem == NULL) + ? EINVAL + : ((WaitForSingleObject (*sem, 0) == WAIT_TIMEOUT) + ? EAGAIN + : 0)); + +} /* sem_trywait */ + + +int +sem_wait (sem_t * sem) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function waits on a semaphore. + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * DESCRIPTION + * This function waits on a semaphore. If the + * semaphore value is greater than zero, it decreases + * its value by one. If the semaphore value is zero, then + * the calling thread (or process) is blocked until it can + * successfully decrease the value or until interrupted by + * a signal. + * + * RESULTS + * 0 successfully destroyed semaphore, + * EINVAL 'sem' is not a valid semaphore, + * ENOSYS semaphores are not supported, + * EINTR the function was interrupted by a signal, + * EDEADLK a deadlock condition was detected. + * + * ------------------------------------------------------ + */ +{ + + return ((sem == NULL) + ? EINVAL + : pthreadCancelableWait (*sem) + ); + +} /* sem_wait */ + + +int +sem_post (sem_t * sem) + /* + * ------------------------------------------------------ + * DOCPUBLIC + * This function posts a wakeup to a semaphore. + * + * PARAMETERS + * sem + * pointer to an instance of sem_t + * + * DESCRIPTION + * This function posts a wakeup to a semaphore. If there + * are waiting threads (or processes), on is awakened; + * otherwise, the semaphore value is incremented by one. + * + * RESULTS + * 0 successfully destroyed semaphore, + * EINVAL 'sem' is not a valid semaphore, + * ENOSYS semaphores are not supported, + * + * ------------------------------------------------------ + */ +{ + return ((sem == NULL) + ? EINVAL + : (ReleaseSemaphore (*sem, 1, 0) + ? 0 + : EINVAL)); + +} /* sem_post */ |