python3之threading模块(上)

布满荆棘的人生 2023-02-10 08:00 70阅读 0赞

threading模块提供了管理多个线程执行的API。

最简单的用法。就是用一个目标函数实例化一个Thread对象。start()开始工作，join()等待当前线程完成。

import threading
    
    
    def work():
        print("working")
    
    for i in range(5):
         t = threading.Thread(target=work)
         t.start()
         print("please wait!")
         t.join()

结果

working
    please wait!
    working
    please wait!
    working
    please wait!
    working
    please wait!
    working

当然也可以传递参数。

import threading
    
    def work(i):
        print("%i is working" %i)
    for i in range(5):
        t = threading.Thread(target=work,args=(i,))
        t.start()
        print("please wait!")
        t.join()

结果

0 is working
    please wait!
    1 is working
    please wait!
    2 is working
    please wait!
    3 is working
    please wait!
    4 is working
    please wait!

### 确定当前线程 ###

每个Thread实例都有一个带有默认值的名字，也可以传入name参数更改。

import threading
    import time
    def work():
        print(threading.current_thread().getName(),"starting!")
        time.sleep(0.5)
        print(threading.current_thread().getName(),"end!")
    
    t = threading.Thread(name="worker", target=work)
    t.start()
    print("please wait!")
    t.join()

结果

worker starting!
    please wait!
    worker end!

出于线程安全的考虑，我们下面用logging模块输出消息。

### 守护线程与非守护线程 ###

**一般来说，程序都会等待所有线程完成工作之后才退出。而守护线程可以一直运行而不阻塞主程序的退出。传入daemon=True或者调用setDaemon()方法并提供参数True来构造守护线程。**

import threading
    import time
    import logging
    
    def daemon():
        logging.debug("start")
        time.sleep(0.5)
        logging.debug("exite")
    
    def non_deamon():
         logging.debug("start")
         logging.debug("exit")
    
    logging.basicConfig(
         level=logging.DEBUG,
         format='(%(threadName)-10s) %(message)s',
     )
    
    d = threading.Thread(name='deamon', target=daemon, daemon=True)
    t = threading.Thread(name="non-deamon", target=non_deamon)
    d.start()
    t.start()

结果中没有看到守护线程的退出的消息，主程序就已经退出了。

(deamon    ) start
    (non-deamon) start
    (non-deamon) exit

要等待一个守护线程结束，需要使用join()方法。默认下，join会无限阻塞，但可以传入浮点值。在时间内线程即使未完成，join也会强制返回。

import threading
    import time
    import logging
    def daemon():
        logging.debug("start")
        time.sleep(0.5)
        logging.debug("exite")
    
    def non_deamon():
        logging.debug("start")
        logging.debug("exit")
    
    logging.basicConfig(
        level=logging.DEBUG,
        format='(%(threadName)-10s) %(message)s',
    )
    
    d = threading.Thread(name='deamon', target=daemon, daemon=True)
    t = threading.Thread(name="non-deamon", target=non_deamon)
    d.start()
    d.join(0.2)
    t.start()

结果还是没有看到守护线程的结束退出的消息。

deamon    ) start
    (non-deamon) start
    (non-deamon) exit

### 枚举所有线程 ###

threading.enumerate()会返回一个Thread实例的一个列表。由于等待当前主程序终止会引入一种死锁的情况，所以跳过这个线程等待。注意根据电脑配置，合理调节线程睡眠时间，否则会由于缺少logging参数而报错。

![image][]

上述程序各个线程执行的顺序

输出顺序可能不一样，

(Thread-1  ) sleeping 2.50
    (Thread-2  ) sleeping 2.00
    (Thread-3  ) sleeping 0.50
    (MainThread) joining Thread-1
    (Thread-3  ) end!
    (Thread-2  ) end!
    (Thread-1  ) end!
    (MainThread) joining Thread-2
    (MainThread) joining Thread-3

[image]: https://imgconvert.csdnimg.cn/aHR0cHM6Ly9pbWcyMDE4LmNuYmxvZ3MuY29tL2Jsb2cvMTMyMjE0NC8yMDE5MDEvMTMyMjE0NC0yMDE5MDEyNTE4NDcyMzkxNi04NDgzMjA0ODQucG5n?x-oss-process=image/format,png