#! /usr/bin/env python

import errno
import fcntl
import sys

FILE = './LOCK_ME.txt'

print 'Python lockf()!'

# Open a file
print 'Opening file {}'.format(FILE)
f = open(FILE, 'a+', 0)

# Lock fun
print 'Acquring lock on {}...'.format(FILE)
try:
    # LOCK_EX to acquire an exclusive lock, no one else gets in
    # LOCK_NB to not block but raise exception if already locked
    fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
except IOError as e:
    if e.errno not in (errno.EACCES, errno.EAGAIN):
        raise
    else:
        print 'Already locked!'
        sys.exit(1)

print 'Locked {}'.format(FILE)
_ = raw_input('Press enter to unlock and exit...')
fcntl.lockf(f, fcntl.LOCK_UN)
f.close()
print 'So long!'