singleton.py

#! /usr/bin/env python

import sys
import os
import errno
import tempfile
import unittest
import logging
from multiprocessing import Process


class SingleInstance:

    """
    If you want to prevent your script from running in parallel just instantiate SingleInstance() class. If is there another instance already running it will exist the application with the message "Another instance is already running, quitting.", returning -1 error code.

    >>> import tendo
    ... me = SingleInstance()

    This option is very useful if you have scripts executed by crontab at small amounts of time.

    Remember that this works by creating a lock file with a filename based on the full path to the script file.
    """

    def __init__(self, flavor_id=""):
        import sys
        self.initialized = False
        basename = os.path.splitext(os.path.abspath(sys.argv[0]))[0].replace("/", "-").replace(":", "").replace("\\", "-") + '-%s' % flavor_id + '.lock'
        # os.path.splitext(os.path.abspath(sys.modules['__main__'].__file__))[0].replace("/", "-").replace(":", "").replace("\\", "-") + '-%s' % flavor_id + '.lock'
        self.lockfile = os.path.normpath(tempfile.gettempdir() + '/' + basename)

        logging.debug("SingleInstance lockfile: " + self.lockfile)
        if sys.platform == 'win32':
            try:
                # file already exists, we try to remove (in case previous execution was interrupted)
                if os.path.exists(self.lockfile):
                    os.unlink(self.lockfile)
                self.fd = os.open(self.lockfile, os.O_CREAT | os.O_EXCL | os.O_RDWR)
            except OSError:
                type, e, tb = sys.exc_info()
                if e.errno == 13:
                    logging.error("Another instance is already running, quitting.")
                    sys.exit(-1)
                print(e.errno)
                raise
        else:  # non Windows
            import fcntl
            self.fp = open(self.lockfile, 'w')
            try:
                fcntl.lockf(self.fp, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except IOError:
                logging.warning("Another instance is already running, quitting.")
                sys.exit(-1)
        self.initialized = True

    def __del__(self):
        import sys
        import os
        if not self.initialized:
            return
        try:
            if sys.platform == 'win32':
                if hasattr(self, 'fd'):
                    os.close(self.fd)
                    os.unlink(self.lockfile)
            else:
                import fcntl
                fcntl.lockf(self.fp, fcntl.LOCK_UN)
                # os.close(self.fp)
                if os.path.isfile(self.lockfile):
                    os.unlink(self.lockfile)
        except Exception as e:
            logging.warning(e)
            sys.exit(-1)