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instance method
File#flock
file.flock(locking_constant) → 0 or false
file.c
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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_thread_io_blocking_region(rb_thread_flock, op, fptr->fd) < 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);
}
Locks or unlocks a file according to locking_constant (a logical or of the values in the table below). Returns false if File::LOCK_NB is specified and the operation would otherwise have blocked. Not available on all platforms.
Locking constants (in class File):
LOCK_EX | Exclusive lock. Only one process may hold an
| exclusive lock for a given file at a time.
----------+------------------------------------------------
LOCK_NB | Don't block when locking. May be combined
| with other lock options using logical or.
----------+------------------------------------------------
LOCK_SH | Shared lock. Multiple processes may each hold a
| shared lock for a given file at the same time.
----------+------------------------------------------------
LOCK_UN | Unlock.
Example:
Example
# update a counter using write lock # don't use "w" because it truncates the file before lock. File.open("counter", File::RDWR|File::CREAT, 0644) {|f| f.flock(File::LOCK_EX) value = f.read.to_i + 1 f.rewind f.write("#{value}\n") f.flush f.truncate(f.pos) } # read the counter using read lock File.open("counter", "r") {|f| f.flock(File::LOCK_SH) p f.read }