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"""
Consistent Hashing demo in Python.
~ 哈希一致性 Python 语言实现
~ 关键抽象
* Entry 放入 cache 服务器中的对象
* Server 真正放入缓存对象的 cache 服务器
* Cluster 服务器集群。（假设会维护一组服务器，这相当于是一组服务器的代理，
接受 put, get 请求，通过一定算法（普通取余或者哈希一致性将请求转发给特定的 server ）
"""
from hashlib import md5
from typing import Dict, List
from collections import OrderedDict
def treemap(dictionary: Dict) -> OrderedDict:
return OrderedDict(sorted(dictionary.items()))
def tail_map(dictionary: Dict, from_key) -> Dict:
tailed_map = {key: value for key, value in dictionary.items() if key >= from_key}
return OrderedDict(tailed_map)
def string_hashcode(key: str, encoding='utf-8') -> int:
m = md5(key.encode(encoding)).hexdigest()
return int(m, 16)
def first_key(dictionary: OrderedDict):
try:
first_item = next(iter(dictionary.items()))
return first_item[0]
except StopIteration as error:
return None
class Entry(str):
_key = ''
def __init__(self, key):
super().__init__()
self._key = key
def __str__(self):
return self._key
class Server:
_name = ''
_entries = {}
def __init__(self, name):
self._name = name
self._entries: Dict[Entry, Entry] = {}
def put(self, e: Entry) -> None:
self._entries[e] = e
def get(self, e: Entry) -> dict:
return self._entries.get(e)
class Cluster:
_SERVER_SIZE_MAX = 1024
_servers = OrderedDict()
_size = 0
def put(self, e: Entry) -> None:
self.route_server(string_hashcode(e)).put(e)
def get(self, e: Entry) -> Entry:
server = self.route_server((string_hashcode(e)))
return server.get(e)
def route_server(self, _hash: int) -> None:
if len(self._servers) == 0:
return None
elif self._servers.get(_hash) is None:
tailed_map = tail_map(self._servers, _hash)
if not bool(tailed_map):
_hash = first_key(self._servers)
else:
_hash = first_key(tailed_map)
return self._servers.get(_hash)
def add_server(self, s: Server) -> bool:
if self._size >= self._SERVER_SIZE_MAX:
return False
else:
self._servers.update({string_hashcode(str(s._name)): s})
self._size = self._size + 1
return True
def create_cluster():
c = Cluster()
c.add_server(Server("192.168.0.0"))
c.add_server(Server("192.168.0.1"))
c.add_server(Server("192.168.0.2"))
c.add_server(Server("192.168.0.3"))
c.add_server(Server("192.168.0.4"))
c.add_server(Server("192.168.0.5"))
return c
def find_entries(c: Cluster, entries: List) -> None:
for e in entries:
if e == c.get(e):
print("重新找到了 entry: {}".format(str(e)))
else:
print("entry {} 已失效".format(str(e)))
def main():
c = create_cluster()
entries = []
entry_items = ["i", "have", "a", "pen", "an", "apple", "applepen",
"pineapple", "pineapplepen", "PPAP"]
for item in entry_items:
entries.append(Entry(item))
for e in entries:
c.put(e)
c.add_server(Server("192.168.0.6"))
c.add_server(Server("11"))
find_entries(c, entries)
if __name__ == "__main__":
main()
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