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Diffstat (limited to 'nuttx/sched/sem_open.c')
-rw-r--r-- | nuttx/sched/sem_open.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/nuttx/sched/sem_open.c b/nuttx/sched/sem_open.c new file mode 100644 index 000000000..cd9ca6129 --- /dev/null +++ b/nuttx/sched/sem_open.c @@ -0,0 +1,206 @@ +/**************************************************************************** + * sched/sem_open.c + * + * Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved. + * Author: Gregory Nutt <spudmonkey@racsa.co.cr> + * + * 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 <nuttx/config.h> + +#include <sys/types.h> +#include <stdbool.h> +#include <stdarg.h> +#include <limits.h> +#include <fcntl.h> +#include <string.h> +#include <semaphore.h> +#include <errno.h> +#include <nuttx/kmalloc.h> +#include "sem_internal.h" + +/**************************************************************************** + * Pre-processor Definitions + ****************************************************************************/ + +/**************************************************************************** + * Private Type Declarations + ****************************************************************************/ + +/**************************************************************************** + * Global Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Function: 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; +} + |