# 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.

from __future__ import absolute_import

import contextlib

import errno

import socket

import time

import warnings

from . import (

    error,

    util,

)

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, vfs, file, timeout=-1, releasefn=None, acquirefn=None,

                 desc=None, inheritchecker=None, parentlock=None):

        self.vfs = vfs

        self.f = file

        self.held = 0

        self.timeout = timeout

        self.releasefn = releasefn

        self.acquirefn = acquirefn

        self.desc = desc

        self._inheritchecker = inheritchecker

        self.parentlock = parentlock

        self._parentheld = False

        self._inherited = False

        self.postrelease  = []

        self.pid = self._getpid()

        self.delay = self.lock()

        if self.acquirefn:

            self.acquirefn()

    def __enter__(self):

        return self

    def __exit__(self, exc_type, exc_value, exc_tb):

        self.release()

    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 _getpid(self):

        # wrapper around util.getpid() to make testing easier

        return util.getpid()

    def lock(self):

        timeout = self.timeout

        while True:

            try:

                self._trylock()

                return self.timeout - timeout

            except error.LockHeld as 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)

        retry = 5

        while not self.held and retry:

            retry -= 1

            try:

                self.vfs.makelock(lockname, self.f)

                self.held = 1

            except (OSError, IOError) as why:

                if why.errno == errno.EEXIST:

                    locker = self._readlock()

                    # special case where a parent process holds the lock -- this

                    # is different from the pid being different because we do

                    # want the unlock and postrelease functions to be called,

                    # but the lockfile to not be removed.

                    if locker == self.parentlock:

                        self._parentheld = True

                        self.held = 1

                        return

                    locker = self._testlock(locker)

                    if locker is not None:

                        raise error.LockHeld(errno.EAGAIN,

                                             self.vfs.join(self.f), self.desc,

                                             locker)

                else:

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

                                                why.filename, self.desc)

    def _readlock(self):

        """read lock and return its value

        Returns None if no lock exists, pid for old-style locks, and host:pid

        for new-style locks.

        """

        try:

            return self.vfs.readlock(self.f)

        except (OSError, IOError) as why:

            if why.errno == errno.ENOENT:

                return None

            raise

    def _testlock(self, locker):

        if locker is None:

            return None

        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.vfs, self.f + '.break', timeout=0)

            self.vfs.unlink(self.f)

            l.release()

        except error.LockError:

            return locker

    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 = self._readlock()

        return self._testlock(locker)

    @contextlib.contextmanager

    def inherit(self):

        """context for the lock to be inherited by a Mercurial subprocess.

        Yields a string that will be recognized by the lock in the subprocess.

        Communicating this string to the subprocess needs to be done separately

        -- typically by an environment variable.

        """

        if not self.held:

            raise error.LockInheritanceContractViolation(

                'inherit can only be called while lock is held')

        if self._inherited:

            raise error.LockInheritanceContractViolation(

                'inherit cannot be called while lock is already inherited')

        if self._inheritchecker is not None:

            self._inheritchecker()

        if self.releasefn:

            self.releasefn()

        if self._parentheld:

            lockname = self.parentlock

        else:

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

        self._inherited = True

        try:

            yield lockname

        finally:

            if self.acquirefn:

                self.acquirefn()

            self._inherited = False

    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 self._getpid() != self.pid:

                # we forked, and are not the parent

                return

            try:

                if self.releasefn:

                    self.releasefn()

            finally:

                if not self._parentheld:

                    try:

                        self.vfs.unlink(self.f)

                    except OSError:

                        pass

            # The postrelease functions typically assume the lock is not held

            # at all.

            if not self._parentheld:

                for callback in self.postrelease:

                    callback()

                # Prevent double usage and help clear cycles.

                self.postrelease = None

def release(*locks):

    for lock in locks:

        if lock is not None:

            lock.release()