Synchronously unlocks the file or part of the file.
Unlocks the byte range from start to end of the file, with
the byte at position end not included. If no arguments are
specified, the full file is unlocked, If only start is
specified the file is unlocked from byte position start to the
end of the file.
NOTE file locking does have slight differences in behavior across platforms:
See lockSync for more details.
Source
void unlockSync([int start = 0, int end = -1]);