如何给Python threading线程加个控制开关

前言

Python3.6.6/threading/threading.Event,如何给每个线程加一个控制开关。

需求分析

在爬虫项目中,threading模块的使用率还是很高的,
每个线程之间独立,如果一个线程成功完成了任务退出了，
其他的线程还要继续跑吗? 会造成资源浪费,如何给线程之间弄个信号源,
一个线程完成任务,其他线程及退出呢?当然可能有很多方法完成目的,
我只把自己使用过的方法做个记录。

实践

test.py

import random
import threading


class Calculation(threading.Thread):

    def __init__(self, signal):
        threading.Thread.__init__(self)
        # 开关控制
        self.singal = signal

    def run(self):
        self.test()
        return

    def test(self):
        while True:
            num = random.randint(0, 100)
            print(threading.currentThread(), num)
            # 如果其他线程完成任务打开开关,当前线程就退出
            if self.singal.isSet():
                print(threading.currentThread(), '其他线程已经完成任务,退出!')
                break
                
            # 如果随机数符合了条件,就把开关打开
            if num == 66:
                print(threading.currentThread(), '当前线程完成任务,退出!')
                self.singal.set()
                break
        return


if __name__ == '__main__':
    # 初始“开关” ，默认值 False
    event_obj = threading.Event()
    # 线程列表
    threads_list = []
    # 开始线程 5个线程
    for thread in range(0, 5):
        threads_list.append(Calculation(signal=event_obj))

    for t in threads_list:
        t.start()

    # for t in threads:
    #     t.join()

看看输出结果,也没什么其他好说的

# 数据太长,删过一部分,重要的流程还在
# \Pythonvenv\py3\Scripts\python.exe test.py
<Calculation(Thread-1, started 24500)> 1
<Calculation(Thread-1, started 24500)> 34
<Calculation(Thread-1, started 24500)> 60
<Calculation(Thread-1, started 24500)> 13
<Calculation(Thread-2, started 24400)> 36
<Calculation(Thread-2, started 24400)> 60
<Calculation(Thread-1, started 24500)> 80
<Calculation(Thread-3, started 13304)> 19
<Calculation(Thread-2, started 24400)> 87
<Calculation(Thread-1, started 24500)> 97
<Calculation(Thread-3, started 13304)> 36
<Calculation(Thread-2, started 24400)> 3
<Calculation(Thread-1, started 24500)> 2
<Calculation(Thread-4, started 18092)> 38
<Calculation(Thread-5, started 16736)> 62
<Calculation(Thread-3, started 13304)> 33
<Calculation(Thread-2, started 24400)> 20
<Calculation(Thread-2, started 24400)> 97
<Calculation(Thread-2, started 24400)> 58
<Calculation(Thread-2, started 24400)> 23
<Calculation(Thread-5, started 16736)> 37
<Calculation(Thread-3, started 13304)> 91
<Calculation(Thread-1, started 24500)> 13
<Calculation(Thread-4, started 18092)> 11
<Calculation(Thread-2, started 24400)> 16
<Calculation(Thread-2, started 24400)> 66
<Calculation(Thread-2, started 24400)> 当前线程完成任务,退出!
<Calculation(Thread-3, started 13304)> 64
<Calculation(Thread-1, started 24500)> 19
<Calculation(Thread-4, started 18092)> 92
<Calculation(Thread-5, started 16736)> 24
<Calculation(Thread-3, started 13304)> 其他线程已经完成任务,退出!
<Calculation(Thread-1, started 24500)> 其他线程已经完成任务,退出!
<Calculation(Thread-4, started 18092)> 其他线程已经完成任务,退出!
<Calculation(Thread-5, started 16736)> 其他线程已经完成任务,退出!

Process finished with exit code 0

知识点

# 定义一个开关
obj = threading.Event() 

# 把开关传进每个线程

# 查看开关的状态,返回True或False,默认值 False
obj.isSet()

# 打开开关,此时值为True
obj.set()

# 关闭开关,此时值为False
obj.clear()

End.