#!/usr/bin/env python #------------------------------------------------------------------------------ # Copyright (c) 2005, Enthought, Inc. # All rights reserved. # # This software is provided without warranty under the terms of the BSD # license included in enthought/LICENSE.txt and may be redistributed only # under the conditions described in the aforementioned license. The license # is also available online at http://www.enthought.com/licenses/BSD.txt # Thanks for using Enthought open source! # # Author: Enthought, Inc. # Description: #------------------------------------------------------------------------------ # GUID.py # Version 2.1. # # Copyright (C) 2003 Dr. Conan C. Albrecht # # This library is free software; you can redistribute it and/or # modify it under the terms of the GNU Lesser General Public # License as published by the Free Software Foundation; either # version 2.1 of the License, or (at your option) any later version. # # This library 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 # Lesser General Public License for more details. # # You should have received a copy of the GNU Lesser General Public # License along with this library; if not, write to the Free Software # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA ################################################################################################## ### A globally-unique identifier made up of time and ip and 8 random digits: 40 characters wide ### ### A globally unique identifier that combines ip, time, and random bits. Since the ### time is listed first, you can sort records by guid. You can also extract the time ### and ip if needed. ### ### GUIDs make wonderful database keys. They require no access to the ### database (to get the max index number), they are extremely unique, and they sort ### automatically by time. GUIDs prevent key clashes when merging ### two databases together, combining data, or generating keys in distributed ### systems. ### ### There is an Internet Draft for UUIDs, but this module does not implement it. ### If the draft catches on, perhaps I'll conform the module to it. ### # Changelog # Sometime, 1997 Created the Java version of GUID # Went through many versions in Java # Sometime, 2002 Created the Python version of GUID, mirroring the Java version # November 24, 2003 Changed Python version to be more pythonic, took out object and made just a module # December 2, 2003 Fixed duplicating GUIDs. Sometimes they duplicate if multiples are created # in the same millisecond (it checks the last 100 GUIDs now and has a larger random part) # December 9, 2003 Fixed MAX_RANDOM, which was going over sys.maxint # import random import socket import sys import time import threading # The size of the circular queue. Larger sizes give more assurance for uniqueness. # Smaller sizes take less memory and are a tiny bit faster QUEUE_SIZE = 100 ############################# ### global module variables MAX_RANDOM = sys.maxint # converted to hex goes to 8 chars (at least, in Python 2.3) rand = random.Random() ip = '' lock = threading.RLock() lastguid = '' try: ip = socket.gethostbyname(socket.gethostname()) except (socket.gaierror): # if we don't have an ip, default to someting in the 10.x.x.x private range ip = '10' for i in range(3): ip += '.' + str(rand.randrange(1, 254)) hexip = ''.join(["%04x" % long(i) for i in ip.split('.')]) # leave space for ip v6 (65K in each sub) ####################################### ### A simple circular set ### to ensure we don't duplicate ### GUIDs in the same millisecond class CircularSet: '''A circular set. A set that maxes at a given size, replacing the oldest element after maximum size. This implementation is NOT thread safe. (generate() below is thread safe, though) ''' def __init__(self): self.queue = [] self.queue_map = {} # for efficiency, we keep a map of everything self.queueindex = 0 def add(self, val): '''Adds a value to the queue''' # check to see if we have this value. If so, throw an exception assert not self.queue_map.has_key(val), 'This value is already in the set!' # add the new one to the list if len(self.queue) > self.queueindex: # first remove the previous key at this location del self.queue_map[self.queue[self.queueindex]] self.queue[self.queueindex] = val else: self.queue.append(val) # now add to the map for efficiency self.queue_map[val] = val # increment the queue index self.queueindex += 1 if self.queueindex >= QUEUE_SIZE: self.queueindex = 0 queue = CircularSet() ################################# ### Public module functions def generate(): '''Generates a new guid''' global lock, queue # since we modify the module variable try: lock.acquire() # can't generate two guids at the same time while 1: parts = [] # time part parts.append("%016x" % (long(time.time() * 1000))) # ip part parts.append(hexip) # random part parts.append(("%08x" % (rand.random() * MAX_RANDOM))[:8]) # limit to 8 chars, just in case maxint goes up in future Pythons # put them all together guid = ''.join(parts) try: queue.add(guid) # throws the AssertionError if this GUID is a duplicate of the queue return guid except AssertionError: # signals we already have this GUID in the queue pass finally: lock.release() def extract_time(guid): '''Extracts the time portion out of the guid and returns the number of seconds since the epoch as a float''' return float(long(guid[0:16], 16)) / 1000 def extract_ip(guid): '''Extracts the ip portion out of the guid and returns it as a string like 10.10.10.10''' # there's probably a more elegant way to do this ip = '' index = 16 while index < 32: if ip != '': ip += "." ip += str(int(guid[index: index + 4], 16)) index += 4 return ip def extract_random(guid): '''Extracts the random bits from the guid (returns the bits in decimal)''' return int(guid[32:], 16) ### TESTING OF GUID CLASS ### if __name__ == "__main__": guid = generate() print "GUID:", guid print "Time:", time.strftime('%a, %d %b %Y %H:%M:%S', time.localtime(extract_time(guid))) print "IP: ", extract_ip(guid) print "Rand:", extract_random(guid)