/* * ------------------------------------------------------------- * * 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) * * 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 * --------------- * * ------------------------------------------------------------- * * 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 */ #include #include #include #include #include "pthread.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, * -1 failed, error in errno * ERRNO * 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; } } if (result != 0) { errno = result; return -1; } return 0; } /* 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, * -1 failed, error in errno * ERRNO * EINVAL 'sem' is not a valid semaphore, * ENOSYS semaphores are not supported, * EBUSY threads (or processes) are currently * blocked on 'sem' * * ------------------------------------------------------ */ { int result = 0; if (sem == NULL) { result = EINVAL; } else if (! CloseHandle (*sem)) { result = EINVAL; } if (result != 0) { errno = result; return -1; } return 0; } /* 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 decreased semaphore, * -1 failed, error in errno * ERRNO * 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. * * ------------------------------------------------------ */ { int result = 0; if (sem == NULL) { result = EINVAL; } else if (WaitForSingleObject (*sem, 0) == WAIT_TIMEOUT) { result = EAGAIN; } if (result != 0) { errno = result; return -1; } return 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 decreased semaphore, * -1 failed, error in errno * ERRNO * 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. * * ------------------------------------------------------ */ { int result = 0; if (sem == NULL) { result = EINVAL; } else { result = pthreadCancelableWait (*sem); } if (result != 0) { errno = result; return -1; } return 0; } /* 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), one is awakened; * otherwise, the semaphore value is incremented by one. * * RESULTS * 0 successfully posted semaphore, * -1 failed, error in errno * ERRNO * EINVAL 'sem' is not a valid semaphore, * ENOSYS semaphores are not supported, * * ------------------------------------------------------ */ { int result = 0; if (sem == NULL) { result = EINVAL; } else if (! ReleaseSemaphore (*sem, 1, 0)) { result = EINVAL; } if (result != 0) { errno = result; return -1; } return 0; } /* sem_post */