multithread file locking test based on http://kzk9.net/blog/2007/05/flock2.html

file locking test

#include <sys/file.h>
#include <pthread.h>
#include <assert.h>
#include <semaphore.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>

static int locked = 0;
static pthread_mutex_t locked_mutex = PTHREAD_MUTEX_INITIALIZER;

int lock_flock(int fd){
  return flock(fd, LOCK_EX);
}

int unlock_flock(int fd){
  return flock(fd, LOCK_UN);
}

int lock_fcntl(int fd){
  struct flock lock;
  lock.l_type = F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start = 0;
  lock.l_len = 0;
  int res = fcntl(fd, F_SETLKW, &lock);
  return res;
}

int unlock_fcntl(int fd){
  struct flock lock;
  int res;
  lock.l_type = F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start = 0;
  lock.l_len = 0;
  if(fcntl(fd, F_GETLK, &lock) < 0){
    // LOCK情報取得失敗
    return -1;
  }else if(lock.l_type == F_UNLCK){
    // 既にLOCKされていなかった
    return 0;
  }

  lock.l_type = F_UNLCK;
  res = fcntl(fd, F_SETLKW, &lock);
  return res;
}


void*
func1(void* arg)
{
  int r;
  char ch = ((char *)arg)[0];
  while (1) {
    FILE *f = fopen("test.txt", "a+");
    assert(f != NULL);
    int fd = fileno(f);
    assert(f >= 0);
    r = lock_fcntl(fd);
    assert(r == 0);
    pthread_mutex_lock(&locked_mutex);
    assert(locked == 0);
    locked = 1;
    pthread_mutex_unlock(&locked_mutex);
    fwrite(&ch, 1, 1, f);
    fwrite(&ch, 1, 1, f);
    printf("%ld\n", pthread_self());
    pthread_mutex_lock(&locked_mutex);
    locked = 0;
    pthread_mutex_unlock(&locked_mutex);
    sched_yield();
    r = unlock_fcntl(fd);
    assert(r == 0);
    fflush(f);
    fclose(f);
  }
  return NULL;
}

#define THREAD_NUM 200
int
main(void)
{
  pthread_t ths[THREAD_NUM];
  int i;
  for (i = 0; i < THREAD_NUM; i++) {
    char ch[1];
    ch[0] = 'a' + i;
    pthread_create(&ths[i], NULL, func1, (void*)ch);
  }
  for (i = 0; i < THREAD_NUM; i++)
    pthread_join(ths[i], NULL);
  return 0;
}