# lock.py - simple advisory 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 version 2 or any later version.

import util, error

import errno, os, socket, time

import warnings

class lock(object):

    '''An advisory lock held by one process to control access to a set

    of files.  Non-cooperating processes or incorrectly written scripts

    can ignore Mercurial's locking scheme and stomp all over the

    repository, so don't do that.

    Typically used via localrepository.lock() to lock the repository

    store (.hg/store/) or localrepository.wlock() to lock everything

    else under .hg/.'''

    # 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.postrelease  = []

        self.pid = os.getpid()

        self.lock()

    def __del__(self):

        if self.held:

            warnings.warn("use lock.release instead of del lock",

                    category=DeprecationWarning,

                    stacklevel=2)

            # ensure the lock will be removed

            # even if recursive locking did occur

            self.held = 1

        self.release()

    def lock(self):

        timeout = self.timeout

        while True:

            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 self.held:

            self.held += 1

            return

        if lock._host is None:

            lock._host = socket.gethostname()

        lockname = '%s:%s' % (lock._host, self.pid)

        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.

        """

        try:

            locker = util.readlock(self.f)

        except OSError, why:

            if why.errno == errno.ENOENT:

                return None

            raise

        try:

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

        except ValueError:

            return locker

        if host != lock._host:

            return locker

        try:

            pid = int(pid)

        except ValueError:

            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', timeout=0)

            util.unlink(self.f)

            l.release()

        except error.LockError:

            return locker

    def release(self):

        """release the lock and execute callback function if any

        If the lock has been acquired multiple times, the actual release is

        delayed to the last release call."""

        if self.held > 1:

            self.held -= 1

        elif self.held == 1:

            self.held = 0

            if os.getpid() != self.pid:

                # we forked, and are not the parent

                return

            if self.releasefn:

                self.releasefn()

            try:

                util.unlink(self.f)

            except OSError:

                pass

            for callback in self.postrelease:

                callback()

def release(*locks):

    for lock in locks:

        if lock is not None:

            lock.release()