kallithea/lib/pidlock.py

# -*- coding: utf-8 -*-
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import errno
import os
from multiprocessing.util import Finalize

from kallithea.lib.compat import kill


class LockHeld(Exception):
    pass


class DaemonLock(object):
    """daemon locking
    USAGE:
    try:
        l = DaemonLock('/path/tolockfile',desc='test lock')
        main()
        l.release()
    except LockHeld:
        sys.exit(1)
    """

    def __init__(self, file_, callbackfn=None,
                 desc='daemon lock', debug=False):
        self.pidfile = file_
        self.callbackfn = callbackfn
        self.desc = desc
        self.debug = debug
        self.held = False
        # run the lock automatically!
        self.lock()
        self._finalize = Finalize(self, DaemonLock._on_finalize,
                                  args=(self, debug), exitpriority=10)

    @staticmethod
    def _on_finalize(lock, debug):
        if lock.held:
            if debug:
                print('lock held finalizing and running lock.release()')
            lock.release()

    def lock(self):
        """
        locking function, if lock is present it
        will raise LockHeld exception
        """
        lockname = str(os.getpid())
        if self.debug:
            print('running lock')
        self.trylock()
        self.makelock(lockname, self.pidfile)
        return True

    def trylock(self):
        running_pid = False
        if self.debug:
            print('checking for already running process')
        try:
            with open(self.pidfile, 'r') as f:
                try:
                    running_pid = int(f.readline())
                except ValueError:
                    running_pid = -1

            if self.debug:
                print('lock file present running_pid: %s, '
                      'checking for execution' % (running_pid,))
            # Now we check the PID from lock file matches to the current
            # process PID
            if running_pid:
                try:
                    kill(running_pid, 0)
                except OSError as exc:
                    if exc.errno in (errno.ESRCH, errno.EPERM):
                        print ("Lock File is there but"
                               " the program is not running")
                        print("Removing lock file for the: %s" % running_pid)
                        self.release()
                    else:
                        raise
                else:
                    print("You already have an instance of the program running")
                    print("It is running as process %s" % running_pid)
                    raise LockHeld()

        except IOError as e:
            if e.errno != 2:
                raise

    def release(self):
        """releases the pid by removing the pidfile
        """
        if self.debug:
            print('trying to release the pidlock')

        if self.callbackfn:
            #execute callback function on release
            if self.debug:
                print('executing callback function %s' % self.callbackfn)
            self.callbackfn()
        try:
            if self.debug:
                print('removing pidfile %s' % self.pidfile)
            os.remove(self.pidfile)
            self.held = False
        except OSError as e:
            if self.debug:
                print('removing pidfile failed %s' % e)
            pass

    def makelock(self, lockname, pidfile):
        """
        this function will make an actual lock

        :param lockname: actual pid of file
        :param pidfile: the file to write the pid in
        """
        if self.debug:
            print('creating a file %s and pid: %s' % (pidfile, lockname))

        dir_, file_ = os.path.split(pidfile)
        if not os.path.isdir(dir_):
            os.makedirs(dir_)
        with open(self.pidfile, 'w') as f:
            f.write(lockname)
        self.held = True