# 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 errno, os, time

import util

class LockException(Exception):

    pass

class LockHeld(LockException):

    pass

class LockUnavailable(LockException):

    pass

class lock(object):

    def __init__(self, file, timeout=-1, releasefn=None):

        self.f = file

        self.held = 0

        self.timeout = timeout

        self.releasefn = releasefn

        self.lock()

    def __del__(self):

        self.release()

    def lock(self):

        timeout = self.timeout

        while 1:

            try:

                self.trylock()

                return 1

            except LockHeld, inst:

                if timeout != 0:

                    time.sleep(1)

                    if timeout > 0:

                        timeout -= 1

                    continue

                raise inst

    def trylock(self):

        pid = os.getpid()

        try:

            util.makelock(str(pid), self.f)

            self.held = 1

        except (OSError, IOError), why:

            if why.errno == errno.EEXIST:

                raise LockHeld(util.readlock(self.f))

            else:

                raise LockUnavailable(why)

    def release(self):

        if self.held:

            self.held = 0

            if self.releasefn:

                self.releasefn()

            try:

                os.unlink(self.f)

            except: pass