platform_bionic/libc/bionic/flockfile.cpp

/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * 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.
 *
 * 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.
 */

#include <errno.h>
#include <stdio.h>

#include "local.h"

// We can't use the OpenBSD implementation which uses kernel-specific
// APIs not available on Linux. Instead we use a pthread_mutex_t within
// struct __sfileext (see fileext.h).

void flockfile(FILE* fp) {
  if (fp != nullptr) {
    pthread_mutex_lock(&_FLOCK(fp));
  }
}

int ftrylockfile(FILE* fp) {
  // The specification for ftrylockfile() says it returns 0 on success,
  // or non-zero on error. So return an errno code directly on error.
  if (fp == nullptr) {
    return EINVAL;
  }

  return pthread_mutex_trylock(&_FLOCK(fp));
}

void funlockfile(FILE* fp) {
  if (fp != nullptr) {
    pthread_mutex_unlock(&_FLOCK(fp));
  }
}