Attachment 1474815 Details for Bug 1507361 – locks program

locks program

locks.c (text/x-csrc), 2.54 KB, created by Raghavendra Bhat on 2018-08-09 20:49:40 UTC

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Creator: Raghavendra Bhat

Created: 2018-08-09 20:49:40 UTC

Size: 2.54 KB

patch

obsolete

>#include <fcntl.h>
>#include <stdio.h>
>#include <stdlib.h>
>#include <unistd.h>
>#include <string.h>
>#include <errno.h>
>#include <sys/stat.h>
>#include <sys/types.h>
>
>
>
>void
>lock_test (int fd)
>{
>
>    char *buffer1 = "aaaaa";
>    char *buffer2 = "bbbbb";
>    int   flag = -1;
>    char *my_buffer = NULL;
>    int ret = -1;
>
>  while (1) {
>    struct flock	fl;
>    memset(&fl, 0, sizeof(fl));
>
>    // lock in shared mode
>    fl.l_type = F_RDLCK;
>
>    // lock entire file
>    fl.l_whence = SEEK_SET;	// offset base is start of the file
>    fl.l_start  = 0;		// starting offset is zero
>    fl.l_len    = 0;		// len is zero, which is a special value representing end
>    // of file (no matter how large the file grows in future)
>
>    // F_SETLKW specifies blocking mode
>    if (fcntl(fd, F_SETLKW, &fl) == -1) {
>      exit(1);
>    }
>
>    // atomically upgrade shared lock to exclusive lock, but only
>    // for bytes in range [10; 15)
>    //
>    // after this call, the process will hold three lock regions:
>    //  [0; 10)        - shared lock
>    //  [10; 15)       - exclusive lock
>    //  [15; SEEK_END) - shared lock
>    fl.l_type  = F_WRLCK;
>    fl.l_start = 10;
>    fl.l_len   = 5;
>
>    // F_SETLKW specifies non-blocking mode
>    if (fcntl(fd, F_SETLK, &fl) == -1) {
>      exit(1);
>    }
>
>    ret = lseek (fd, 10, SEEK_SET);
>    if (ret == -1) {
>      fprintf (stderr, "seeking to the offset 10 failed (%s)\n",
>	       strerror (errno));
>      goto unlock;
>    }
>
>    if (flag == -1 || flag == 1) {
>      my_buffer = buffer1;
>      flag = 0;
>    } else {
>      flag = 1;
>      my_buffer = buffer2;
>    }
>
>    ret = write (fd, my_buffer, strlen (my_buffer));
>      if (ret == -1)
>	fprintf (stderr, "failed to write the buffer %s to the\n"
>		 "file (error: %s)\n", buffer1, strerror (errno));
>
>  unlock:
>    // release lock for bytes in range [10; 15)
>    fl.l_type = F_UNLCK;
>
>    if (fcntl(fd, F_SETLK, &fl) == -1) {
>      exit(1);
>    }
>
>    // close file and release locks for all regions
>    // remember that locks are released when process calls close()
>    // on any descriptor for a lock file
>    //close(fd);
>
>    printf ("finished one run\n");
>    sleep (5);
>  }
>
>  return;
>}
>
>int main (int argc, char *argv[])
>{
>
>  char *file_name = argv[1];
>  int   fd        = -1;
>  int   ret       = -1;
>
>  /*
>   * Assumes the file to be created already. Not that intelligent
>   */
>
>  fd = open (file_name, O_RDWR);
>  if (fd == -1) {
>    fprintf (stderr, "open failed on %s (%s)\n", file_name, strerror (errno));
>    goto out;
>  }
>
>  lock_test (fd);
>
>  ret = 0;
>
>out:
>  if (fd)
>    close (fd);
>
>  return ret;
>}

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Attachments on bug 1507361: 1474815