# -*- coding: utf-8 -*-

"""

一致性哈希算法 python实现

参考

http://weblogs.java.net/blog/2007/11/27/consistent-hashing

http://code.google.com/p/flexihash/

http://www.codinglabs.org/html/consistent-hashing.html

"""

import hashlib

class ConsistentHash(object):

def __init__(self, hasher=None, replicas=None):

self.hasher = hasher and hasher or hashlib.md5

self.replicas = replicas and replicas or 64

self.positionToTarget = {}

self.targetToPositions = {}

self.targetCount = 0

def addTarget(self, target):

self.targetToPositions[target] = []

for i in range(self.replicas):

position = self.hasher(str(target)+str(i)).hexdigest()

self.positionToTarget[position] = target

self.targetToPositions[target].append(position)

self.targetCount += 1

def addTargets(self, targets):

for target in targets:

self.addTarget(target)

def removeTarget(self, target):

if self.targetToPositions.has_key(target):

for position in self.targetToPositions[target]:

self.positionToTarget.pop(position)

self.targetToPositions.pop(target)

self.targetCount -= 1

def getAllTargets(self):

return self.targetToPositions.keys()

def lookupList(self, resource, requestedCount):

if not self.positionToTarget:

return []

resourcePosition = self.hasher(resource).hexdigest()

results = []

collect = False

for key in sorted(self.positionToTarget.keys()):

value = self.positionToTarget[key]

if not collect and key > resourcePosition:

collect = True

if collect and value not in results:

results.append(value)

if len(results) == requestedCount or \

len(results) == self.targetCount:

return results

for key in sorted(self.positionToTarget.keys()):

value = self.positionToTarget[key]

if value not in results:

results.append(value)

if len(results) == requestedCount or \

len(results) == self.targetCount:

return results

return results

def lookup(self, resource):

targets = self.lookupList(resource, 1)

return targets[0]