# lock.py - simple locking scheme for mercurial

#

# Copyright 2005 Matt Mackall <mpm@selenic.com>

#

# This software may be used and distributed according to the terms

# of the GNU General Public License, incorporated herein by reference.

import os, time

class LockHeld(Exception):

    pass

class lock:

    def __init__(self, file, wait = 1):

        self.f = file

        self.held = 0

        self.wait = wait

        self.lock()

    def __del__(self):

        self.release()

    def lock(self):

        while 1:

            try:

                self.trylock()

                return 1

            except LockHeld, inst:

                if self.wait:

                    time.sleep(1)

                    continue

                raise inst

    def trylock(self):

        pid = os.getpid()

        try:

            os.symlink(str(pid), self.f)

            self.held = 1

        except:

            raise LockHeld(os.readlink(self.f))

    def release(self):

        if self.held:

            self.held = 0

            os.unlink(self.f)