redis -- setnx 实现分布式锁

不念不忘少年蓝@ 2021-10-19 15:46 310阅读 0赞

**SETNX key value  
只有在 key 不存在时设置 key 的值。存在的话，在执行后，返回结果是0；不存在值，进行设置的话，返回结果是1。**

先用python实现两个线程交替运行

import time
    from threading import Thread
    
    def task1():
        while True:
            print("this is task1")
            time.sleep(1)
    
    def task2():
        while True:
            print("this is task2")
            time.sleep(1)
    
    t1 = Thread(target=task1)
    t2 = Thread(target=task2)
    t1.start()
    t2.start()

运行结果如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70]

现在用上多线程的互斥锁

import time
    from threading import Thread, Lock
    
    i = 5
    
    def task1():
        while True:
            global i
            i += 1
            if i % 3 == 0:
                print("this is task1", i)
                lock2.acquire()
                lock1.release()
                time.sleep(1)
    
    def task2():
        while True:
            global i
            i += 1
            if i % 5 == 0:
                print("this is task2", i)
                lock1.acquire()
                lock2.release()
                time.sleep(1)
    
    lock1 = Lock()
    lock2 = Lock()
    t1 = Thread(target=task1)
    t2 = Thread(target=task2)
    lock1.acquire()
    t1.start()
    t2.start()

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70 1]  
使用redis的setnx，可以实现分布式锁的功能

import redis
    import time
    from threading import Thread, Lock
    
    i = 5
    res = redis.Redis(host='localhost', port=6379, db=9)
    
    def task1():
        while True:
            global i
            i += 1
            res.delete("lock")
            if i % 3 == 0:
                if res.setnx("lock", "11"):
                    print("this is task1", i)
                    time.sleep(1)
    
    def task2():
        while True:
            global i
            i += 1
            res.delete("lock")
            if i % 3 == 0:
                if res.setnx("lock", "11"):
                    print("this is task2", i)
                    time.sleep(1)
    
    t1 = Thread(target=task1)
    t2 = Thread(target=task2)
    res.setnx("lock", "22")
    t1.start()
    t2.start()

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70 2]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70]: /images/20211019/beb56168bf7e4082a714f310bdc2f188.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70 1]: /images/20211019/186279103a6541aab5a782c6e755f63b.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d5bWFpc3ls_size_16_color_FFFFFF_t_70 2]: /images/20211019/62ff3f1a0a0846478d831ece92b6cd23.png