1. 守護(hù)線程

1. 使用setDaemon(True)把所有的子線程都變成了主線程的守護(hù)線程，因此當(dāng)主進(jìn)程結(jié)束后，子線程也會(huì)隨之結(jié)束。所以當(dāng)主線程結(jié)束后，整個(gè)程序就退出了。
2. 把子進(jìn)程設(shè)置為守護(hù)線程，必須在start()之前設(shè)置。
3. 為了讓守護(hù)線程執(zhí)行結(jié)束之后，主線程再結(jié)束，我們可以使用join方法，讓主線程等待子線程執(zhí)行
4. join()在start()之后。

#!/usr/bin/env python
# coding:utf-8


import threading
import time


def run(n):
    print(f'task {n}')
    time.sleep(1)
    print('2s')
    time.sleep(1)
    print('1s')
    time.sleep(1)
    print('0s')
    time.sleep(1)


if __name__ == '__main__':
    t1 = threading.Thread(target=run, args=('t1',))
    t1.setDaemon(True)  # 把子進(jìn)程設(shè)置為守護(hù)線程，必須在start()之前設(shè)置
    t1.start()
    t1.join()  # 設(shè)置主線程等待子線程結(jié)束
    print('main thread end.')

2. 多線程共享全局變量

1. 線程是進(jìn)程的執(zhí)行單元，進(jìn)程是系統(tǒng)分配資源的最小單位，所以在同一個(gè)進(jìn)程中的多線程是共享資源的。

#!/usr/bin/env python
# coding:utf-8

import threading
import time

global_num = 100


def work1():
    global global_num
    for i in range(3):
        global_num += 1
    print(f'in work1 global_num is :{global_num}')


def work2():
    global global_num
    print(f'in work2 global_num is {global_num}')


if __name__ == '__main__':
    t1 = threading.Thread(target=work1)
    t1.start()
    time.sleep(1)
    t2 = threading.Thread(target=work2)
    t2.start()
# output:
in work1 global_num is :103
in work2 global_num is 103