Python：Child进程退出，使其线程继续运行

Question

While working on a project using the multiprocessing module in python I observed some strange behaviour.

Lets assume that my main program p1 created a process p2 using multiprocessing module. The process p2 created a thread in itself called p2_t1 . There is no code block in p2 after creating this thread, so it exits(i am NOT calling exit, so it would just return from main) leaving p2_t1 dangling. I can confirm this via strace

Example code in p1 that creates a child process

p = Process(target=RunService,args=(/*some args*/),name="p2")

Example code of p2 :

def RunService():
    try:
        /*do something here*/
    except Exception,e:
        /*create a new thread*/

    /*nothing here so basically this process exits leaving the thread dangling*/

This however does not happen if a thread(call is p1_t1 ) is created within p1 . p1 doesnot exit until the created thread p1_t1 runs.

Example code in this case for p1

try:
  /*do something here*/
except Exception,e:
  /*create a new thread*/

    /*nothing here so basically process should end*/

In this case the process doesnot exit and keeps running until the thread is running. Any explanations?

Answer 1

Without any code to speak of, it is hard to tell what's happening, but I would try making your thread a daemon thread and then wait on it with p2. When the tread finished, then p2 should shut down properly, killing off the thread. Something like this:

t1 = threading.Thread(target=somefunc, args=((2,)))
t1.setDaemon(True)
t1.start()
t1.join()

good luck, Mike