Method: File#flock

Defined in:

file.c

#flock(operation) ⇒ Object

:markup: markdown

call-seq:

flock(locking_constant) -> 0 or false

Locks or unlocks file self according to the given ‘locking_constant`, a bitwise OR of the values in the table below.

Not available on all platforms.

Returns ‘false` if `File::LOCK_NB` is specified and the operation would have blocked; otherwise returns `0`.

| Constant | Lock | Effect |—————–|————–|—————————————————————————————————————–| | File::LOCK_EX | Exclusive | Only one process may hold an exclusive lock for self at a time. | | File::LOCK_NB | Non-blocking | No blocking; may be combined with File::LOCK_SH or File::LOCK_EX using the bitwise OR operator \|. | | File::LOCK_SH | Shared | Multiple processes may each hold a shared lock for self at the same time. | | File::LOCK_UN | Unlock | Remove an existing lock held by this process. |

Example:

“‘ruby # Update a counter using an exclusive lock. # Don’t use File::WRONLY because it truncates the file. File.open(‘counter’, File::RDWR | File::CREAT, 0644) do |f|

f.flock(File::LOCK_EX)
value = f.read.to_i + 1
f.rewind
f.write("#{value}\n")
f.flush
f.truncate(f.pos)

end

# Read the counter using a shared lock. File.open(‘counter’, ‘r’) do |f|

f.flock(File::LOCK_SH)
f.read

end “‘

# File 'file.c', line 5377

static VALUE
rb_file_flock(VALUE obj, VALUE operation)
{
    rb_io_t *fptr;
    int op[2], op1;
    struct timeval time;

    op[1] = op1 = NUM2INT(operation);
    GetOpenFile(obj, fptr);
    op[0] = fptr->fd;

    if (fptr->mode & FMODE_WRITABLE) {
        rb_io_flush_raw(obj, 0);
    }
    while ((int)rb_io_blocking_region(fptr, rb_thread_flock, op) < 0) {
        int e = errno;
        switch (e) {
          case EAGAIN:
          case EACCES:
#if defined(EWOULDBLOCK) && EWOULDBLOCK != EAGAIN
          case EWOULDBLOCK:
#endif
            if (op1 & LOCK_NB) return Qfalse;

            time.tv_sec = 0;
            time.tv_usec = 100 * 1000;	/* 0.1 sec */
            rb_thread_wait_for(time);
            rb_io_check_closed(fptr);
            continue;

          case EINTR:
#if defined(ERESTART)
          case ERESTART:
#endif
            break;

          default:
            rb_syserr_fail_path(e, fptr->pathv);
        }
    }
    return INT2FIX(0);
}