python 线程 实现多任务

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主线程创建子线程，子线程不执行完毕的话主线程不会销毁。主线程是给子线程收尸的。

python使用threading模块创建多线程

1. 没有多任务的程序

import time


def sing():
    """唱歌 5秒钟"""
    for i in range(5):
        print("----正在唱:菊花茶----")
        time.sleep(1)


def dance():
    """跳舞 5秒钟"""
    for i in range(5):
        print("----正在跳舞----")
        time.sleep(1)


def main():
    sing()
    dance()


if __name__ == "__main__":
    main()

2. 多任务 线程

import time
import threading


def sing():
    """唱歌 5秒钟"""
    for i in range(5):
        print("----正在唱:菊花茶----")
        time.sleep(1)


def dance():
    """跳舞 5秒钟"""
    for i in range(5):
        print("----正在跳舞----")
        time.sleep(1)


def main():
    t1 = threading.Thread(target=sing)
    t2 = threading.Thread(target=dance)
    t1.start()
    t2.start()


if __name__ == "__main__":
    main()

3.让某些线程先执行

import threading
import time


def test1():
    for i in range(5):
        print("-----test1---%d---" % i)


def test2():
    for i in range(5):
        print("-----test2---%d---" % i)


def main():
    t1 = threading.Thread(target=test1)
    t2 = threading.Thread(target=test2)

    t1.start()

    time.sleep(1)
    print("---1---")

    t2.start()

    time.sleep(1)
    print("---2---")

    print(threading.enumerate())


if __name__ == "__main__":
    main()

4. 循环查看当前运行的线程

import threading
import time


def test1():
    for i in range(5):
        print("-----test1---%d---" % i)
        time.sleep(1)

    # 如果创建Thread时执行的函数，运行结束那么意味着 这个子线程结束了....


def test2():
    for i in range(10):
        print("-----test2---%d---" % i)
        time.sleep(1)


def main():
    t1 = threading.Thread(target=test1)
    t2 = threading.Thread(target=test2)

    t1.start()
    t2.start()

    while True:
        print(threading.enumerate())
        if len(threading.enumerate())<=1:
            break
        time.sleep(1)


if __name__ == "__main__":
    main()

5. 验证创建线程以及运行时间

import threading
import time


def test1():
    for i in range(5):
        print("-----test1---%d---" % i)
        time.sleep(1)


def main():
    # 在调用Thread之前先打印当前线程信息
    print(threading.enumerate())
    t1 = threading.Thread(target=test1)

    # 在调用Thread之后打印
    print(threading.enumerate())

    t1.start()

    # 在调用start之后打印
    print(threading.enumerate())

if __name__ == "__main__":
    main()

6.线程共享全局变量

import threading
import time

# 定义一个全局变量
g_num = 100


def test1():
    global g_num
    g_num += 1
    print("-----in test1 g_num=%d----" % g_num)


def test2():
    print("-----in test2 g_num=%d=----" % g_num)


def main():
    t1 = threading.Thread(target=test1)
    t2 = threading.Thread(target=test2)

    t1.start()
    time.sleep(1)

    t2.start()
    time.sleep(1)

    print("-----in main Thread g_num = %d---" % g_num)

if __name__ == "__main__":
    main()

import threading
import time

def test1(temp):
    temp.append(33)
    print("-----in test1 temp=%s----" % str(temp))


def test2(temp):
    print("-----in test2 temp=%s----" % str(temp))


g_nums = [11, 22]

def main():
    # target指定将来 这个线程去哪个函数执行代码
    # args指定将来调用 函数的时候 传递什么数据过去
    t1 = threading.Thread(target=test1, args=(g_nums,))
    t2 = threading.Thread(target=test2, args=(g_nums,))

    t1.start()
    time.sleep(1)

    t2.start()
    time.sleep(1)

    print("-----in main Thread g_nums = %s---" % str(g_nums))

if __name__ == "__main__":
    main()

7.共享全局变量出现的问题 - 资源竞争

import threading
import time

# 定义一个全局变量
g_num = 0


def test1(num):
    global g_num
    for i in range(num):
        g_num += 1
    print("-----in test1 g_num=%d----" % g_num)


def test2(num):
    global g_num
    for i in range(num):
        g_num += 1
    print("-----in test2 g_num=%d=----" % g_num)


def main():
    t1 = threading.Thread(target=test1, args=(1000000,))
    t2 = threading.Thread(target=test2, args=(1000000,))

    t1.start()
    t2.start()

    # 等待上面的2个线程执行完毕....
    time.sleep(5)

    print("-----in main Thread g_num = %d---" % g_num)

if __name__ == "__main__":
    main()

8. 使用互斥锁解决资源竞争的问题

import threading
import time

# 定义一个全局变量
g_num = 0


def test1(num):
    global g_num
    # 上锁，如果之前没有被上锁，那么此时 上锁成功
    # 如果上锁之前 已经被上锁了，那么此时会堵塞在这里，直到 这个锁被解开位置
    mutex.acquire()
    for i in range(num):
        g_num += 1
    # 解锁
    mutex.release()
    print("-----in test1 g_num=%d----" % g_num)


def test2(num):
    global g_num
    mutex.acquire()
    for i in range(num):
        g_num += 1
    mutex.release()
    print("-----in test2 g_num=%d=----" % g_num)


# 创建一个互斥锁，默认是没有上锁的
mutex = threading.Lock()


def main():
    t1 = threading.Thread(target=test1, args=(1000000,))
    t2 = threading.Thread(target=test2, args=(1000000,))

    t1.start()
    t2.start()

    # 等待上面的2个线程执行完毕....
    time.sleep(2)

    print("-----in main Thread g_num = %d---" % g_num)

if __name__ == "__main__":
    main()

import threading
import time

# 定义一个全局变量
g_num = 0


def test1(num):
    global g_num

    for i in range(num):
        mutex.acquire()  # 上锁
        g_num += 1
        mutex.release()  # 解锁
    print("-----in test1 g_num=%d----" % g_num)


def test2(num):
    global g_num
    for i in range(num):
        mutex.acquire()  # 上锁
        g_num += 1
        mutex.release()  # 解锁
    print("-----in test2 g_num=%d=----" % g_num)


# 创建一个互斥锁，默认是没有上锁的
mutex = threading.Lock()


def main():
    t1 = threading.Thread(target=test1, args=(1000000,))
    t2 = threading.Thread(target=test2, args=(1000000,))

    t1.start()
    t2.start()

    # 等待上面的2个线程执行完毕....
    time.sleep(2)

    print("-----in main Thread g_num = %d---" % g_num)

if __name__ == "__main__":
    main()

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