【python教程】对多线程中join()的详细教程

怼烎@ 2022-09-12 10:59 144阅读 0赞

在 Python 的多线程编程中，经常碰到 thread.join()这样的代码。那么今天咱们用实际代码来解释一下 join 函数的作用。

**一、**  
当一个进程启动之后，会默认产生一个主线程，因为线程是程序执行流的最小单元，当设置多线程时，主线程会创建多个子线程，在python中，默认情况下（其实就是setDaemon(False)），主线程执行完自己的任务以后，就退出了，此时子线程会继续执行自己的任务，直到自己的任务结束，例子见下面。

# 测试多线程中join的功能
    import threading, time
    def doWaiting():
        print 'start waiting1: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(3)
        print 'stop waiting1: ' + time.strftime('%H:%M:%S') + "\n"
    def doWaiting1():
        print 'start waiting2: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(8)
        print 'stop waiting2: ', time.strftime('%H:%M:%S') + "\n"
    tsk = []
    thread1 = threading.Thread(target = doWaiting)
    thread1.start()
    tsk.append(thread1)
    thread2 = threading.Thread(target = doWaiting1)
    thread2.start()
    tsk.append(thread2)
    print 'start join: ' + time.strftime('%H:%M:%S') + "\n"
    
    print 'end join: ' + time.strftime('%H:%M:%S') + "\n"

代码执行结果如下：

start waiting1: 22:24:20
    
    start join: 22:24:20
    start waiting2: 22:24:20
    
    
    end join: 22:24:20
    
    stop waiting1: 22:24:23
    
    stop waiting2:  22:24:28

**二、**  
当我们使用setDaemon(True)方法，设置子线程为守护线程时，主线程一旦执行结束，则全部线程全部被终止执行，可能出现的情况就是，子线程的任务还没有完全执行结束，就被迫停止，例子见下面。

# 测试多线程中join的功能
    ''' 学习中遇到问题没人解答？小编创建了一个Python学习交流QQ群：531509025 寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！ '''
    import threading, time
    def doWaiting():
        print 'start waiting1: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(3)
        print 'stop waiting1: ' + time.strftime('%H:%M:%S') + "\n"
    def doWaiting1():
        print 'start waiting2: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(8)
        print 'stop waiting2: ', time.strftime('%H:%M:%S') + "\n"
    tsk = []
    thread1 = threading.Thread(target = doWaiting)
    thread1.setDaemon(True)
    thread1.start()
    tsk.append(thread1)
    thread2 = threading.Thread(target = doWaiting1)
    thread2.setDaemon(True)
    thread2.start()
    tsk.append(thread2)
    print 'start join: ' + time.strftime('%H:%M:%S') + "\n"
    
    print 'end join: ' + time.strftime('%H:%M:%S') + "\n"

代码执行结果如下：

start waiting1: 22:34:46
    
    start waiting2: 22:34:46
    start join: 22:34:46
    
    
    end join: 22:34:46

**三、**  
没有设置守护线程且没有设置join函数的timeout参数时，主线程将会一直等待，直到子线程全部结束，主线程才结束，程序退出。

代码如下：

# 测试多线程中join的功能
    import threading, time
    def doWaiting():
        print 'start waiting1: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(3)
        print 'stop waiting1: ' + time.strftime('%H:%M:%S') + "\n"
    def doWaiting1():
        print 'start waiting2: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(8)
        print 'stop waiting2: ', time.strftime('%H:%M:%S') + "\n"
    tsk = []
    thread1 = threading.Thread(target = doWaiting)
    thread1.start()
    tsk.append(thread1)
    thread2 = threading.Thread(target = doWaiting1)
    thread2.start()
    tsk.append(thread2)
    print 'start join: ' + time.strftime('%H:%M:%S') + "\n"
    for tt in tsk:
        tt.join()
    print 'end join: ' + time.strftime('%H:%M:%S') + "\n"

代码执行结果如下：

start waiting1: 22:41:50
    
    start join: 22:41:50
    start waiting2: 22:41:50
    
    
    stop waiting1: 22:41:53
    
    stop waiting2:  22:41:58
    
    end join: 22:41:58

**四、**  
当没有设置守护线程且join函数的参数timeout=2时，主线程将会等待多个子线程timeout的累加和这样的一段时间，时间一到，主线程结束，但是并没有杀死子线程，子线程依然可以继续执行，直到子线程全部结束，程序退出。

代码如下：

# 测试多线程中join的功能
    ''' 学习中遇到问题没人解答？小编创建了一个Python学习交流QQ群：531509025 寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！ '''
    import threading, time
    def doWaiting():
        print 'start waiting1: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(3)
        print 'stop waiting1: ' + time.strftime('%H:%M:%S') + "\n"
    def doWaiting1():
        print 'start waiting2: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(8)
        print 'stop waiting2: ', time.strftime('%H:%M:%S') + "\n"
    tsk = []
    thread1 = threading.Thread(target = doWaiting)
    thread1.start()
    tsk.append(thread1)
    thread2 = threading.Thread(target = doWaiting1)
    thread2.start()
    tsk.append(thread2)
    print 'start join: ' + time.strftime('%H:%M:%S') + "\n"
    for tt in tsk:
        tt.join(2)
    print 'end join: ' + time.strftime('%H:%M:%S') + "\n"

代码执行结果如下：

start waiting1: 23:02:34
    
    start waiting2: 23:02:34
    start join: 23:02:34
    
    
    stop waiting1: 23:02:37
    
    end join: 23:02:38
    
    stop waiting2:  23:02:42

**五、**  
当设置守护线程join函数的参数timeout=2时，主线程将会等待多个子线程timeout的累加和这样的一段时间，时间一到，主线程结束，杀死未执行完的子线程，程序退出。

代码如下：

# 测试多线程中join的功能
    ''' 学习中遇到问题没人解答？小编创建了一个Python学习交流QQ群：531509025 寻找有志同道合的小伙伴，互帮互助,群里还有不错的视频学习教程和PDF电子书！ '''
    import threading, time
    def doWaiting():
        print 'start waiting1: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(3)
        print 'stop waiting1: ' + time.strftime('%H:%M:%S') + "\n"
    def doWaiting1():
        print 'start waiting2: ' + time.strftime('%H:%M:%S') + "\n"
        time.sleep(8)
        print 'stop waiting2: ', time.strftime('%H:%M:%S') + "\n"
    tsk = []
    thread1 = threading.Thread(target = doWaiting)
    thread1.setDaemon(True)
    thread1.start()
    tsk.append(thread1)
    thread2 = threading.Thread(target = doWaiting1)
    thread2.setDaemon(True)
    thread2.start()
    tsk.append(thread2)
    print 'start join: ' + time.strftime('%H:%M:%S') + "\n"
    for tt in tsk:
        tt.join(2)
    print 'end join: ' + time.strftime('%H:%M:%S') + "\n"

代码执行结果如下：

start waiting1: 23:23:57
    
    start waiting2: 23:23:57
    start join: 23:23:57
    
    
    stop waiting1: 23:24:00
    
    end join: 23:24:01