/************************************************************************
* lib/misc/lib_filesem.c
*
* Copyright (C) 2007, 2009, 2011 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 <unistd.h>
#include <semaphore.h>
#include <errno.h>
#include <assert.h>
#include "lib_internal.h"
#if CONFIG_STDIO_BUFFER_SIZE > 0
/************************************************************************
* Pre-processor Definitions
************************************************************************/
/************************************************************************
* Private Data
************************************************************************/
/************************************************************************
* Global Functions
************************************************************************/
/************************************************************************
* lib_sem_initialize
************************************************************************/
void lib_sem_initialize(FAR struct file_struct *stream)
{
/* Initialize the LIB semaphore to one (to support one-at-
* a-time access to private data sets.
*/
(void)sem_init(&stream->fs_sem, 0, 1);
stream->fs_holder = -1;
stream->fs_counts = 0;
}
/************************************************************************
* lib_take_semaphore
************************************************************************/
void lib_take_semaphore(FAR struct file_struct *stream)
{
pid_t my_pid = getpid();
/* Do I already have the semaphore? */
if (stream->fs_holder == my_pid)
{
/* Yes, just increment the number of references that I have */
stream->fs_counts++;
}
else
{
/* Take the semaphore (perhaps waiting) */
while (sem_wait(&stream->fs_sem) != 0)
{
/* The only case that an error should occr here is if
* the wait was awakened by a signal.
*/
ASSERT(get_errno() == EINTR);
}
/* We have it. Claim the stak and return */
stream->fs_holder = my_pid;
stream->fs_counts = 1;
}
}
/************************************************************************
* lib_give_semaphore
************************************************************************/
void lib_give_semaphore(FAR struct file_struct *stream)
{
pid_t my_pid = getpid();
/* I better be holding at least one reference to the semaphore */
ASSERT(stream->fs_holder == my_pid);
/* Do I hold multiple references to the semphore */
if (stream->fs_counts > 1)
{
/* Yes, just release one count and return */
stream->fs_counts--;
}
else
{
/* Nope, this is the last reference I have */
stream->fs_holder = -1;
stream->fs_counts = 0;
ASSERT(sem_post(&stream->fs_sem) == 0);
}
}
#endif /* CONFIG_STDIO_BUFFER_SIZE */
