/**************************************************************************** * sched/sem_open.c * * Copyright (C) 2007, 2008, 2012 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name NuttX nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include #include #include #include "sem_internal.h" /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /**************************************************************************** * Private Type Declarations ****************************************************************************/ /**************************************************************************** * Global Variables ****************************************************************************/ /**************************************************************************** * Private Variables ****************************************************************************/ /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: sem_open * * Description: * This function establishes a connection between named semaphores and a * task. Following a call to sem_open() with the semaphore name, the task * may reference the semaphore associated with name using the address * returned by this call. The semaphore may be used in subsequent calls * to sem_wait(), sem_trywait(), and sem_post(). The semaphore remains * usable until the semaphore is closed by a successful call to sem_close(). * * If a task makes multiple calls to sem_open() with the same name, then * the same semaphore address is returned (provided there have been no * calls to sem_unlink()). * * Parameters: * name - Semaphore name * oflag - Semaphore creation options. This may either or both of the * following bit settings. * oflag = 0: Connect to the semaphore only if it already exists. * oflag = O_CREAT: Connect to the semaphore if it exists, otherwise * create the semaphore. * oflag = O_CREAT|O_EXCL: Create a new semaphore * unless one of this name already exists. * Optional parameters. When the O_CREAT flag is specified, two optional * parameters are expected: * 1. mode_t mode (ignored), and * 2. unsigned int value. This initial value of the semaphore. Valid * initial values of the semaphore must be less than or equal to * SEM_VALUE_MAX. * * Return Value: * A pointer to sem_t or -1 (ERROR) if unsuccessful. * * Assumptions: * ****************************************************************************/ FAR sem_t *sem_open (FAR const char *name, int oflag, ...) { int namelen; FAR nsem_t *psem; FAR sem_t *sem = (FAR sem_t*)ERROR; va_list arg; /* Points to each un-named argument */ mode_t mode; /* Creation mode parameter (ignored) */ unsigned int value; /* Semaphore value parameter */ /* Make sure that a non-NULL name is supplied */ if (name) { /* The POSIX specification requires that the "check for the * existence of a semaphore and the creation of the semaphore * if it does not exist shall be atomic with respect to other * processes executing sem_open()..." A simple sched_lock() * should be sufficient to meet this requirement. */ sched_lock(); namelen = strlen(name); if (namelen > 0) { /* See if the semaphore already exists */ psem = sem_findnamed(name); if (psem) { /* It does. Check if the caller wanted to created * a new semahore with this name. */ if (!(oflag & O_CREAT) || !(oflag & O_EXCL)) { /* Allow a new connection to the semaphore */ psem->nconnect++; sem = &psem->sem; } } /* It doesn't exist. Should we create one? */ else if ((oflag & O_CREAT) != 0) { /* Set up to get the optional arguments needed to create * a message queue. */ va_start(arg, oflag); mode = va_arg(arg, mode_t); value = va_arg(arg, unsigned int); /* Verify that a legal initial value was selected. */ if (value <= SEM_VALUE_MAX) { /* Allocate memory for the new semaphore */ psem = (FAR nsem_t*)kmalloc((sizeof(nsem_t) + namelen + 1)); if (psem) { /* Initialize the named semaphore */ sem = &psem->sem; sem_init(sem, 0, value); psem->nconnect = 1; psem->unlinked = false; psem->name = (FAR char*)psem + sizeof(nsem_t); strcpy(psem->name, name); /* Add the new semaphore to the list of named * semaphores */ dq_addfirst((FAR dq_entry_t*)psem, &g_nsems); } /* Clean-up variable argument stuff */ va_end(arg); } } } sched_unlock(); } return sem; }