The role of python thread join

Few facts

1 python default parameters after the thread is created, regardless of whether the main thread is executed, will wait for the child thread to complete the execution before exiting, with or without join results

2 If the thread is created and the daemon is set to true, that is, thread.setDaemon(True), the main thread will automatically exit after execution, and will not wait for the execution result of the child thread. And as the main thread exits, the child thread also dies.

3 The role of the join method is blocking, waiting for the end of the child thread, the join method has a parameter is timeout, that is, if the main thread waits for timeout, the child thread has not finished, the main thread forcibly ends the child thread.

4 If the thread daemon attribute is False, the timeout parameter in the join is invalid. The main thread will wait for the end of the child thread.

5 If the thread daemon attribute is True, the timeout parameter in the join is valid. The main thread will wait for the timeout time and end the child thread. There is a pit here, that is, if there are N child threads join (timeout) at the same time, then the main thread will wait for the maximum timeout of N * timeout, because each child thread's timeout start time is the last child thread timeout. Moment.

Test code and run results:

import threading, time

def doThreadTest():

print 'start thread time:', time.strftime('%H:%M:%S')

time.sleep(10)

print 'stop thread time:', time.strftime('%H:%M:%S')

threads = []

for i in range(3):

thread1 = threading.Thread(target = doThreadTest)

thread1.setDaemon(True)

threads.append(thread1)

for t in threads:

t.start()

for t in threads:

t.join(1)

print 'stop main thread'

If comment out thread1.setDaemon(True), the result is

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