多线程笔记

多线程,适用于 io 密集型
1.子线程没有运行结束时,主线程不要运行
用到join()方法,会将其阻塞在,在主线程结束后,对其释放

start_time = time.time()
t1 = threading.Thread(target=get_list_html)
t2 = threading.Thread(target=get_detail_html)
t1.start()
t2.start()
t1.join()
t2.join()

print(time.time() - start_time)

2.主线程不需要等待子线程结束,只要主线程结束,子线程就强制结束.守护线程,守护线程要在开始之前

t1.setDaemon(True)
t2.setDaemon(True)
t1.start()
t2.start()

3.线程间的通信:
3.1通过全局变量通信

import time
import threading

detail_url_list = []


class GetListHtml(threading.Thread):

    def __init__(self, url_list):
        super(GetListHtml, self).__init__()
        self.url_list = url_list

    def run(self):
        print('开始获取列表页')
        for i in range(30):
            time.sleep(1)
            url = f'www.baidu.com/{i}'
            self.url_list.append(url)
            print('已经获取到列表页')


class GetDetailHtml(threading.Thread):

    def __init__(self, url_list):
        super(GetDetailHtml, self).__init__()
        self.url_list = url_list

    def run(self):
        while True:
            if self.url_list:
                print('开始获取列表页详情')
                url = self.url_list.pop()
                print(f'已经获取到列表页-{url}')
                time.sleep(2)


if __name__ == '__main__':
    t1 = GetListHtml(detail_url_list)
    t2 = GetDetailHtml(detail_url_list)
    t3 = GetDetailHtml(detail_url_list)
    t1.start()
    t2.start()
    t3.start()

3.2多线程的安全性,不安全
用安全的队列 from queue import Queue
join里面有计数器,会在put的时候加1,task_done的时候减一,当局计数器是0的时候,会马上阻塞

加锁
lock.acquire(),lock.release
死锁,资源竞争的情况