# lock.py - simple locking scheme for mercurial

#

# Copyright 2005, 2006 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, socket, time, util, error

class lock(object):

    # lock is symlink on platforms that support it, file on others.

    # symlink is used because create of directory entry and contents

    # are atomic even over nfs.

    # old-style lock: symlink to pid

    # new-style lock: symlink to hostname:pid

    _host = None

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

        self.f = file

        self.held = 0

        self.timeout = timeout

        self.releasefn = releasefn

        self.desc = desc

        self.lock()

    def __del__(self):

        self.release()

    def lock(self):

        timeout = self.timeout

        while 1:

            try:

                self.trylock()

                return 1

            except error.LockHeld, inst:

                if timeout != 0:

                    time.sleep(1)

                    if timeout > 0:

                        timeout -= 1

                    continue

                raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,

                                     inst.locker)

    def trylock(self):

        if lock._host is None:

            lock._host = socket.gethostname()

        lockname = '%s:%s' % (lock._host, os.getpid())

        while not self.held:

            try:

                util.makelock(lockname, self.f)

                self.held = 1

            except (OSError, IOError), why:

                if why.errno == errno.EEXIST:

                    locker = self.testlock()

                    if locker is not None:

                        raise error.LockHeld(errno.EAGAIN, self.f, self.desc,

                                             locker)

                else:

                    raise error.LockUnavailable(why.errno, why.strerror,

                                                why.filename, self.desc)

    def testlock(self):

        """return id of locker if lock is valid, else None.

        If old-style lock, we cannot tell what machine locker is on.

        with new-style lock, if locker is on this machine, we can

        see if locker is alive.  If locker is on this machine but

        not alive, we can safely break lock.

        The lock file is only deleted when None is returned.

        """

        locker = util.readlock(self.f)

        try:

            host, pid = locker.split(":", 1)

        except ValueError:

            return locker

        if host != lock._host:

            return locker

        try:

            pid = int(pid)

        except:

            return locker

        if util.testpid(pid):

            return locker

        # if locker dead, break lock.  must do this with another lock

        # held, or can race and break valid lock.

        try:

            l = lock(self.f + '.break')

            l.trylock()

            os.unlink(self.f)

            l.release()

        except error.LockError:

            return locker

    def release(self):

        if self.held:

            self.held = 0

            if self.releasefn:

                self.releasefn()

            try:

                os.unlink(self.f)

            except: pass