基于redis的分布式锁--python实现

Posted 2020-11-26 狂飙的指尖

直接上代码

 1 # coding=utf-8
 2 
 3 
 4 # 使用redis实现分布式锁的原因
 5 # 1 redis性能好
 6 # 2 redis命令对此支持较好，实现起来比较方便
 7 
 8 """
 9 redis命令介绍
10     setnx key val  当且仅当key不存在时，set一个key为val的字符串，返回1；若key存在，则什么都不做，返回0
11     expire key timeout  为key设置一个超时时间，单位为second，超过这个时间锁会自动释放，避免死锁
12     delete key  删除key
13 """
14 import time
15 import uuid
16 from threading import Thread
17 
18 import redis
19 
20 redis_client = redis.Redis(host="localhost", port=6379, db=2)
21 
22 
23 def acquire_lock(lock_str, acquire_time=10, time_out=10):
24     """设置锁"""
25     lock_key = "string:lock:" + lock_str
26     identifier_uuid_str = str(uuid.uuid4())
27     end = time.time() + acquire_time
28 
29     try:
30         while time.time() < end:
31             if redis_client.setnx(lock_key, identifier_uuid_str):
32                 # 设置超时时间，防止进程崩溃导致其他进程无法获取锁
33                 redis_client.expire(lock_key, time=time_out)
34                 return identifier_uuid_str
35 
36             elif not redis_client.ttl(lock_key):
37                 redis_client.expire(lock_key, time=time_out)
38             time.sleep(0.01)
39     finally:
40         # 释放锁
41         redis_client.delete(lock_key)
42         return False
43 
44 
45 def release_lock(lock_str, identifier_uuid_str):
46     """释放锁"""
47     lock = "string:lock:" + lock_str
48     pip = redis_client.pipeline(True)
49     while True:
50         try:
51             pip.watch(lock)
52             lock_value = redis_client.get(lock)
53             if not lock_value:
54                 return True
55 
56             if lock_value.decode() == identifier_uuid_str:
57                 pip.multi()
58                 pip.delete(lock)
59                 pip.execute()
60                 return True
61             pip.unwatch()
62             break
63         except redis.exceptions.WatchError:
64             pass
65     return False
66 
67 
68 # 秒杀demo
69 def seckill(product_id, t_id):
70     identifier_uuid_str = acquire_lock(product_id)
71     if not identifier_uuid_str:
72         return "error"
73     print "线程:{}--获得了锁".format(t_id)
74     stock = int(redis_client.get("stock"))
75     if stock > 0:
76         real_stock = stock - 1
77         redis_client.set("stock", str(real_stock))
78         print "线程:{}--抢到一件商品，剩余库存{}件".format(t_id, real_stock)
79     else:
80         print "线程:{}--没抢到，库存不足".format(t_id)
81         return
82     release_lock(product_id, identifier_uuid_str)
83     print "线程:{}--释放了锁".format(i)
84 
85 
86 # redis-cli: set stock 20
87 for i in range(25):
88     product_id = "product_001"
89     t = Thread(target=seckill, args=(product_id, i,))
90     t.start()

实际还存在一个问题，如果任务的执行时间超过了锁的有效期，就会导致其他进程获取锁，会出现释放的锁并非当前任务加的锁的情况，这里可以另开一个线程在一定时间内不断为锁续命。