多线程4

多线程4

为了等待线程执行完毕，除了多线程2中提到的join，还可以使用本文的lock。

以下代码展示未使用lock的情况：

import threading


def thread1_job():
    global A
    for i in range(10):
        A += 1
        print('thread1', A)

def thread2_job():
    global A
    for i in range(10):
        A += 10
        print('thread2', A)


if __name__ == '__main__':
    A = 0
    t1 = threading.Thread(target=thread1_job)
    t2 = threading.Thread(target=thread2_job)
    t1.start()
    t2.start()

输出结果：

thread1 1
thread1 2
thread1 3
thread1 4
thread2thread1  14
thread2 25
15
thread1 26
thread1 27
thread1 thread228
 thread138 
thread2 39
49
thread2thread1 60
 59
thread2 70
thread2 80
thread2 90
thread2 100
thread2 110

thread1和thread2同时对global变量A进行操作，表现为交替对A+1或者+10。

如果我们想要等thread1执行完再执行其他步骤，那就可以用上lock：

import threading


def thread1_job():
    global A, lock
    lock.acquire()
    for i in range(10):
        A += 1
        print('thread1', A)
    lock.release()

def thread2_job():
    global A
    for i in range(10):
        A += 10
        print('thread2', A)


if __name__ == '__main__':
    A = 0
    lock = threading.Lock()
    t1 = threading.Thread(target=thread1_job)
    t2 = threading.Thread(target=thread2_job)
    t1.start()
    t2.start()

输出结果：

thread1 1
thread1 2
thread1 3
thread1 4
thread1 5
thread1 6
thread1 7
thread1 8
thread1 9
thread1 10
thread2 20
thread2 30
thread2 40
thread2 50
thread2 60
thread2 70
thread2 80
thread2 90
thread2 100
thread2 110

此时lock的acquire和release之间的任务执行完毕后，才执行其他任务。