flock_nb

#!/usr/bin/env python
# 
# Script to open and flock its first argument
#
# then exec the rest of its args
#
# Original source:
#
# https://github.com/thorfi/simple-scripts

import errno
import fcntl
import os
import sys
import time

def usage_exit():
    print >>sys.stderr, "Usage: %s /path/to/lock.file command to run" \
        % (sys.argv[0],)
    sys.exit(0)

def iso_time(utc_epoch = None):
    return time.strftime('%Y-%m-%dT%H:%M:%S%z', time.localtime(utc_epoch))

def oserr_exit(exc, filename = None):
    suffix = ''
    if exc.filename is None and filename is not None:
        suffix = ': %r' % (filename,)
    print >>sys.stderr, "%s: %s%s" % (sys.argv[0], exc, suffix)
    sys.exit(1)
    os._exit(1)

################################################################################
def main():
    if len(sys.argv) < 3:
        usage_exit()

    start_t = time.time()
    oexcl_path = sys.argv[1]
    try:
        oexcl_fd = os.open(oexcl_path, os.O_RDWR|os.O_CREAT)
    except OSError, exc:
        oserr_exit(exc, oexcl_path)
        assert False
    try:
        fcntl.flock(oexcl_fd, fcntl.LOCK_EX|fcntl.LOCK_NB)
        flock_t = time.time()
        #fcntl.lockf(oexcl_fd, fcntl.LOCK_EX|fcntl.LOCK_NB)
        #lockf_t = time.time()
    except OSError, exc:
        if exc.errno in (errno.EAGAIN, ):
            sys.exit(1)
            os._exit(1)
        oserr_exit(exc, oexcl_path)
        assert False
    except IOError, exc:
        if exc.errno in (errno.EAGAIN, ):
            sys.exit(1)
            os._exit(1)
        oserr_exit(exc, oexcl_path)
        assert False
    os.write(oexcl_fd,
        "%s\nmain() %s\nflock()ed %s\nsys.argv = %r\n" \
        % (os.getpid(),
            iso_time(start_t), iso_time(flock_t),
            sys.argv,))
    try:
        os.execvp(sys.argv[2], sys.argv[2:])
    except OSError, exc:
        oserr_exit(exc, sys.argv[2])
        assert False
    sys.exit(255)
    os._exit(255)
    assert False

################################################################################
if __name__=="__main__":
    main()
#EOF