Simple File Cache Between Python Processes

Here is a simple way to cache pickled data between multiple Python processes.

#!/usr/bin/env python

from __future__ import with_statement

import cPickle as pickle
import os
import sys
import time

CACHE_TTL = 300    # seconds
LOCK_TTL = 60
DATA_FILE = '/tmp/pickle_file'
LOCK_FILE = '/tmp/pickle_lock'

def get_data():
    data_store = {}
    locked = False
    if os.path.exists(LOCK_FILE):
        lock_file_info = os.stat(LOCK_FILE)
        # Check if lock file is stale
        if lock_file_info[9] + LOCK_TTL < time.mktime(time.localtime()):
            os.remove(LOCK_FILE)
        else:
            locked = True
    if not os.path.exists(DATA_FILE):
        lock_file_obj = open(LOCK_FILE, 'w')
        data_store = refresh_data()
        data_file_obj = open(DATA_FILE, 'w')
        pickle.Pickler(data_file_obj).dump(data_store)
        data_file_obj.close()
        lock_file_obj.close()
        os.remove(LOCK_FILE)
    else:
        data_file_obj = open(DATA_FILE, 'r')
        data_store = pickle.Unpickler(data_file_obj).load()
        data_file_obj.close()
        if not locked:
            if time.mktime(time.localtime()) > data_store['expire']:
                lock_file_obj = open(LOCK_FILE, 'w')
                data_store = refresh_data()
                data_file_obj = open(DATA_FILE, 'w')
                pickle.Pickler(data_file_obj).dump(data_store)
                data_file_obj.close()
                lock_file_obj.close()
                os.remove(LOCK_FILE)
    return data_store

def refresh_data():
    """
    Only needs to return a dictionary with 'expire' key set
    """
    data_store = {}
    with open('/dev/random', 'r') as rnd:
        data_store['k1'] = rnd.readline()
    data_store['expire'] = time.mktime(time.localtime()) + CACHE_TTL
    return data_store


print get_data()