对Python线程中join步骤的疑问

对Python线程中join方法的疑问
代码如下：
import threading
import time
from random import randint

class MyThread(threading.Thread):
    def __init__(self,id):
        threading.Thread.__init__(self)
        self.id=id
    def run(self):
        x = randint(1,10)
        time.sleep(x)
        print "Thread %d sleeped %d sec." % (self.id, x)

def main():
    threads = []
    for i in range(10):
        threads.append(MyThread(i))

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

    print "main done!"

if __name__=="__main__":
    main()

结果：
Thread 4 sleeped 1 sec.
Thread 5 sleeped 1 sec.
Thread 9 sleeped 1 sec.
Thread 0 sleeped 2 sec.
Thread 3 sleeped 4 sec.
Thread 7 sleeped 6 sec.
Thread 8 sleeped 6 sec.
Thread 1 sleeped 7 sec.
Thread 2 sleeped 8 sec.
Thread 6 sleeped 8 sec.
main done!

在main()里执行t.join(), 我的理解应该是main所在的线程挂起，直到t执行完后再执行main.
当第一个t.join()后，main挂起，执行”Thread 0“. 但为什么for循环里的't.join()'语句在‘Thread 0’结束前就又执行了？
‘t.join()’在main里，应该是main的一部分。为什么它没有被挂起，还是照常执行？
而 print "main done!", 与main一起挂起了，直到Thead 0-9都结束后才执行？

------解决方案--------------------

引用:

在main()里执行t.join(), 我的理解应该是main所在的线程挂起，直到t执行完后再执行main.

确实是这样,见下面代码运行的输出.

引用:

当第一个t.join()后，main挂起，执行”Thread 0“. 但为什么for循环里的't.join()'语句在‘Thread 0’结束前就又执行了？

你怎么知道"for循环里的't.join()'语句在‘Thread 0’结束前就又执行了"?如果for循环继续执行了,"main done"应该是最先输出的,但你的运行结果不是这样.

下面的例子更明显一些:



import threading

import time

from random import randint


class MyThread(threading.Thread):

    def __init__(self,id):

        threading.Thread.__init__(self)

        self.id=id

    def run(self):

        x = randint(1,10)

        time.sleep(x)

        print "Thread %d sleeped %d sec." % (self.id, x)


def main():

    threads = []

    for i in range(10):

        threads.append(MyThread(i))

    

    for t in threads:

        t.start()

    for t in threads:

        print "waiting for thread:", t.id

        t.join()

        print "thread", t.id, "ended."


    print "main done!"


if __name__=="__main__":

    main()

输出:



waiting for thread: 0

Thread 3 sleeped 1 sec.

Thread 5 sleeped 4 sec.

Thread 9 sleeped 6 sec.

Thread 0 sleeped 7 sec.

thread 0 ended.

waiting for thread: 1

Thread 8 sleeped 9 sec.

 Thread 6 sleeped 9 sec.

Thread 7 sleeped 9 sec.

Thread 1 sleeped 10 sec.

thread 1 ended.

waiting for thread: 2

Thread 4 sleeped 10 sec.

Thread 2 sleeped 10 sec.

thread 2 ended.

waiting for thread: 3

thread 3 ended.

waiting for thread: 4

thread 4 ended.

waiting for thread: 5

thread 5 ended.

waiting for thread: 6

thread 6 ended.

waiting for thread: 7

thread 7 ended.

waiting for thread: 8

thread 8 ended.

waiting for thread: 9

thread 9 ended.

main done!

对Python线程中join步骤的疑问

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