forked from Archive/PX4-Autopilot
146 lines
4.6 KiB
C
146 lines
4.6 KiB
C
/************************************************************************
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* lib/misc/lib_filesem.c
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*
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* Copyright (C) 2007, 2009, 2011 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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************************************************************************/
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/************************************************************************
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* Included Files
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************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <semaphore.h>
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#include <errno.h>
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#include <assert.h>
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#include "lib_internal.h"
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#if CONFIG_STDIO_BUFFER_SIZE > 0
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/************************************************************************
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* Pre-processor Definitions
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************************************************************************/
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/************************************************************************
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* Private Data
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************************************************************************/
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/************************************************************************
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* Global Functions
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************************************************************************/
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/************************************************************************
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* lib_sem_initialize
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************************************************************************/
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void lib_sem_initialize(FAR struct file_struct *stream)
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{
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/* Initialize the LIB semaphore to one (to support one-at-
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* a-time access to private data sets.
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*/
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(void)sem_init(&stream->fs_sem, 0, 1);
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stream->fs_holder = -1;
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stream->fs_counts = 0;
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}
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/************************************************************************
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* lib_take_semaphore
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************************************************************************/
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void lib_take_semaphore(FAR struct file_struct *stream)
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{
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pid_t my_pid = getpid();
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/* Do I already have the semaphore? */
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if (stream->fs_holder == my_pid)
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{
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/* Yes, just increment the number of references that I have */
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stream->fs_counts++;
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}
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else
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{
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/* Take the semaphore (perhaps waiting) */
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while (sem_wait(&stream->fs_sem) != 0)
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{
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/* The only case that an error should occr here is if
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* the wait was awakened by a signal.
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*/
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ASSERT(get_errno() == EINTR);
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}
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/* We have it. Claim the stak and return */
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stream->fs_holder = my_pid;
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stream->fs_counts = 1;
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}
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}
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/************************************************************************
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* lib_give_semaphore
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************************************************************************/
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void lib_give_semaphore(FAR struct file_struct *stream)
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{
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pid_t my_pid = getpid();
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/* I better be holding at least one reference to the semaphore */
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ASSERT(stream->fs_holder == my_pid);
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/* Do I hold multiple references to the semphore */
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if (stream->fs_counts > 1)
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{
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/* Yes, just release one count and return */
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stream->fs_counts--;
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}
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else
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{
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/* Nope, this is the last reference I have */
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stream->fs_holder = -1;
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stream->fs_counts = 0;
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ASSERT(sem_post(&stream->fs_sem) == 0);
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}
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}
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#endif /* CONFIG_STDIO_BUFFER_SIZE */
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