Implementa semaphoro para controle de blocos atômicos em arquivo.

semaphore.py

# -*- coding: utf-8 -*-
"""Implements semaphoro to control atomic blocks on file."""
# by sx.slex@gmail.com
import os
import sys
import uuid
import time
import signal


class Semaphone(object):
    """Implements semaphoro to control atomic blocks on file."""

    def __init__(self, lockfile):
        self.lockfile = lockfile
        self._exit = False
        self._last = None

        def signal_handler(signal, frame):
            self._exit = True
            self.release()
            sys.exit(0)

        signal.signal(signal.SIGINT or signal.SIGTERM, signal_handler)

    def _ismy(self, myhash):
        try:
            return open(
                self.lockfile, 'r').read().split(None)[0] == myhash
        except:
            return False

    def acquire(self):
        myhash = uuid.uuid4().hex
        while True:
            while os.path.exists(self.lockfile):
                time.sleep(0.05)
            if not self._exit:
                open(self.lockfile, 'a+').write(myhash + '\n')
                if self._ismy(myhash):
                    self._last = myhash
                    return True
            time.sleep(0.05)

    def release(self):
        if self._ismy(self._last):
            os.unlink(self.lockfile)
        time.sleep(0.1)
        return True

    def __enter__(self):
        self.acquire()
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.release()
        return True if exc_type is None else False

if __name__ == '__main__':
    from threading import Thread
    import random

    semaphore = Semaphone('.teste_semaphore')

    def task(i):
        while True:
            with semaphore:
                print('BEGIN TASK: {}'.format(i))
                time.sleep(random.randint(1, 3))
                print('END TASK..: {}'.format(i))
    for i in range(5):
        t = Thread(target=task, args=(i,)).start()