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author | patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3> | 2007-02-17 23:21:28 +0000 |
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committer | patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3> | 2007-02-17 23:21:28 +0000 |
commit | e3940eb2080711edac189cca3f642ee89dc215f2 (patch) | |
tree | 1c390958fae49e34dce698b175487e6d4681e540 /nuttx/sched/sem_open.c | |
parent | 2223612deb2cc6322992f8595b6d6f86fcb53ae1 (diff) | |
download | px4-nuttx-e3940eb2080711edac189cca3f642ee89dc215f2.tar.gz px4-nuttx-e3940eb2080711edac189cca3f642ee89dc215f2.tar.bz2 px4-nuttx-e3940eb2080711edac189cca3f642ee89dc215f2.zip |
NuttX RTOS
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3 42af7a65-404d-4744-a932-0658087f49c3
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..f6139ec5e --- /dev/null +++ b/nuttx/sched/sem_open.c @@ -0,0 +1,206 @@ +/************************************************************ + * sem_open.c + * + * Copyright (C) 2007 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 Gregory Nutt 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 <sys/types.h> +#include <stdarg.h> +#include <string.h> +#include <semaphore.h> +#include <nuttx/kmalloc.h> +#include "sem_internal.h" + +/************************************************************ + * Compilation Switches + ************************************************************/ + +/************************************************************ + * 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_MAX_VALUE. + * + * Return Value: + * A pointer to sem_t or -1 (ERROR) if unsuccessful. + * + * Assumptions: + * + ************************************************************/ + +sem_t *sem_open (const char *name, int oflag, ...) +{ + int namelen; + nsem_t *psem; + sem_t *sem = (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_MAX_VALUE) + { + /* Allocate memory for the new semaphore */ + + psem = (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 = (char*)psem + sizeof(nsem_t); + strcpy(psem->name, name); + + /* Add the new semaphore to the list of named + * semaphores + */ + + dq_addfirst((dq_entry_t*)psem, &g_nsems); + } + + /* Clean-up variable argument stuff */ + + va_end(arg); + } + } + } + sched_unlock(); + } + + return sem; +} |