python之线程锁

本文讲python中的四种锁
Lock互斥锁
使用前

num = 0


def a():
    global num
    for _ in range(10000000):
        num += 1


def b():
    global num
    for _ in range(10000000):
        num += 1


if __name__ == '__main__':
    t1=Thread(target=a)
    t1.start()
    t2=Thread(target=b)
    t2.start()
    t1.join()
    t2.join()
    print(num)    #基本永远会小于20000000

使用后

num = 0


def a(lock):
    global num
    for _ in range(1000000):
        with lock:
            num += 1


def b(lock):
    global num
    for _ in range(1000000):
        with lock:
            num += 1


if __name__ == '__main__':
    lock = threading.Lock()
    t1=Thread(target=a, args=(lock,))
    t1.start()
    t2=Thread(target=b, args=(lock,))
    t2.start()
    t1.join()
    t2.join()
    print(num)    #永远会输出20000000

RLock重用锁

#在之前的代码中永远不可能出现锁在没释放之前重新获得锁，但rlock可以做到，但只能发生在一个线程中，如：
num = 0


def a(lock):
    with lock:
        print("我是A")
        b(lock)


def b(lock):
    with lock:
        print("我是b")

if __name__ == '__main__':
    lock = threading.Lock()
    t1 = Thread(target=a, args=(lock,))
    t1.start()    #会发生死锁，因为在第一次还没释放锁后，b就准备上锁，并阻止a释放锁

使用后

if __name__ == '__main__':
    lock = threading.RLock()    #只需要改变锁为RLock程序马上恢复
    t1 = Thread(target=a, args=(lock,))
    t1.start()

Condition同步锁

#这个程序我们模拟甲乙对话
Jlist = ["在吗", "干啥呢", "去玩儿不", "好吧"]
Ylist = ["在呀", "玩儿手机", "不去"]


def J(list):
    for i in list:
        print(i)
        time.sleep(0.1)


def Y(list):
    for i in list:
        print(i)
        time.sleep(0.1)


if __name__ == '__main__':
    t1 = Thread(target=J, args=(Jlist,))
    t1.start()
    t1.join()
    t2 = Thread(target=Y, args=(Ylist,))
    t2.start()
    t2.join()    #上面的程序输出后发现效果就是咱们想要的，但是我们每次输出后都要等待0.1秒，也无法正好确定可以拿到时间片的最短时间值，并且不能保证每次正好都是另一个线程执行。因此，我们用以下方式，完美解决这些问题。

使用后

Jlist = ["在吗", "干啥呢", "去玩儿不", "好吧"]
Ylist = ["在呀", "玩儿手机", "不去","哦"]


def J(cond, list):
    for i in list:
        with cond:
            print(i)
            cond.notify()
            cond.wait()


def Y(cond, list):
    for i in list:
        with cond:
            cond.wait()
            print(i)
            cond.notify()


if __name__ == '__main__':
    cond = threading.Condition()
    t1 = Thread(target=J, args=(cond, Jlist))
    t2 = Thread(target=Y, args=(cond, Ylist))
    t2.start()
    t1.start()    #一定保证t1启动在t2之后,因为notify发送的信号要被t2接受到，如果t1先启动，会发生阻塞。

Seamplore信号量
使用前

class B(threading.Thread):
    def __init__(self, name):
        super().__init__()
        self.name = name

    def run(self):
        time.sleep(1)
        print(self.name)


class A(threading.Thread):
    def __init__(self):
        super().__init__()

    def run(self):
        for i in range(100):
            b = B(i)
            b.start()


if __name__ == '__main__':
    a = A()
    a.start()    #执行后发现不断在输出

使用后

class B(threading.Thread):
    def __init__(self, name, sem):
        super().__init__()
        self.name = name
        self.sem = sem

    def run(self):
        time.sleep(1)
        print(self.name)
        sem.release()


class A(threading.Thread):
    def __init__(self, sem):
        super().__init__()
        self.sem = sem

    def run(self):
        for i in range(100):
            self.sem.acquire()
            b = B(i, self.sem)
            b.start()


if __name__ == '__main__':
    sem = threading.Semaphore(value=3)
    a = A(sem)
    a.start()    #通过执行上面的代码，我们发现一次只能输出三个数字，sem控制访问并发量

Event事件

import time
import threading


class MyThread(threading.Thread):
    def __init__(self, name, event):
        super().__init__()
        self.name = name
        self.event = event

    def run(self):
        print('Thread: {} start at {}'.format(self.name, time.ctime(time.time())))
        # 等待event.set()后，才能往下执行
        self.event.wait()
        print('Thread: {} finish at {}'.format(self.name, time.ctime(time.time())))


event = threading.Event()

# 定义五个线程
threads = [MyThread(str(i), event) for i in range(1,5)]

# 重置event，使得event.wait()起到阻塞作用
event.clear()

# 启动所有线程
[t.start() for t in threads]

print('等待5s...')
time.sleep(5)

print('唤醒所有线程...')
event.set()

# output:
'''
Thread: 1 start at Sun May 13 20:38:08 2018
Thread: 2 start at Sun May 13 20:38:08 2018
Thread: 3 start at Sun May 13 20:38:08 2018
Thread: 4 start at Sun May 13 20:38:08 2018

等待5s...

唤醒所有线程...
Thread: 1 finish at Sun May 13 20:38:13 2018
Thread: 4 finish at Sun May 13 20:38:13 2018
Thread: 2 finish at Sun May 13 20:38:13 2018
Thread: 3 finish at Sun May 13 20:38:13 2018
'''