nuttx/libs/libc/misc/lib_filesem.c

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/****************************************************************************
* libs/libc/misc/lib_filesem.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include <nuttx/semaphore.h>
#include <nuttx/fs/fs.h>
#include "libc.h"
#ifndef CONFIG_STDIO_DISABLE_BUFFERING
/****************************************************************************
* Public 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.
*/
_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();
int ret;
/* 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 ((ret = _SEM_WAIT(&stream->fs_sem)) < 0)
{
/* The only case that an error should occr here is if the wait
* was awakened by a signal.
*/
DEBUGASSERT(_SEM_ERRNO(ret) == EINTR ||
_SEM_ERRNO(ret) == ECANCELED);
UNUSED(ret);
}
/* 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)
{
/* I better be holding at least one reference to the semaphore */
DEBUGASSERT(stream->fs_holder == getpid());
/* 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;
DEBUGVERIFY(_SEM_POST(&stream->fs_sem));
}
}
#endif /* CONFIG_STDIO_DISABLE_BUFFERING */