Cherrypy tool for exclusive lock. MethodDispatcher.

lock.py

# -*- coding: utf-8 -*-
import cherrypy

from random import randint
from fcntl import flock, LOCK_EX, LOCK_UN

__all__ = ["LockTool"]

class LockTool(cherrypy.Tool):
    def __init__(self):
        cherrypy.Tool.__init__(self, 'before_handler',
                               self.acquire,
                               priority=9)

    def _setup(self):
        cherrypy.Tool._setup(self)
        cherrypy.request.hooks.attach('before_finalize',
                                      self.release,
                                      priority=90)
        cherrypy.request.hooks.attach('after_error_response',
                                      self.release,
                                      priority=90)

    def acquire(self, key=None, methods=["POST", "PUT", "DELETE"]):
        if cherrypy.request.method in methods:
            parameter = key + cherrypy.request.params[key] if key else 'global'
            lock = ExclusiveLock(parameter)
            lock.lock()
            cherrypy.request.lock = lock

    def release(self):
        if hasattr(cherrypy.request, 'lock'):
            lock = cherrypy.request.lock
            lock.unlock()

class ExclusiveLock():
    key = None #user given value
    file = None  #resource to lock
    own = False #have we locked resource

    def __init__(self, key):
        self.id = randint(0, 1000)
        self.key = key
        #create a new resource or get exisitng with same key
        self.file = open("/tmp/%s.lockfile" % key, 'w+')

    def __del__(self):
        if self.own == True:
            self.unlock()

    def lock(self):
        flock(self.file, LOCK_EX)
        self.file.truncate(0) # truncate file
        #write something to just help debugging
        self.file.write("Locked\n");
        self.file.flush()
        self.own = True
        cherrypy.engine.log('Lock<%d> %s ACQUIRED' % (self.id, self.key))
        return self.own

    def unlock(self):
        if self.own == True:
            flock(self.file, LOCK_UN)
            self.file.truncate(0) # truncate file
            #write something to just help debugging
            self.file.write("Unlocked\n")
            self.file.flush()
            cherrypy.engine.log('Lock<%d> %s RELEASED' % (self.id, self.key))
        else:
            pass
        self.own = False
        return self.own