CODEWITHSUNDEEP
pythonmultithreading
Toam
Toam

Reputation: 1010

Programmatically exiting python script while multithreading

I have some code which runs routinely, and every now and then (like once a month) the program seems to hang somewhere and I'm not sure where.

I thought I would implement [what has turned out to be not quite] a "quick fix" of checking how long the program has been running for. I decided to use multithreading to call the function, and then while it is running, check the time.

For example:

import datetime
import threading

def myfunc():
  #Code goes here

t=threading.Thread(target=myfunc)
t.start()
d1=datetime.datetime.utcnow()
while threading.active_count()>1:
  if (datetime.datetime.utcnow()-d1).total_seconds()>60:
    print 'Exiting!'
    raise SystemExit(0)

However, this does not close the other thread (myfunc).

What is the best way to go about killing the other thread?

Upvotes: 2

Views: 1102

Answers (2)

Mark Mikofski
Mark Mikofski

Reputation: 20178

There is no way to kill a thread. You must kill the target from within the target. The best way is with a hook and a queue. It goes something like this.

import Threading
from Queue import Queue

# add a kill_hook arg to your function, kill_hook
# is a queue used to pass messages to the main thread
def myfunc(*args, **kwargs, kill_hook=None):
  #Code goes here
  # put this somewhere which is periodically checked.
  # an ideal place to check the hook is when logging
  try:
    if q.get_nowait():  # or use q.get(True, 5) to wait a longer
      print 'Exiting!'
      raise SystemExit(0)
    except Queue.empty:
      pass

q = Queue()  # the queue used to pass the kill call
t=threading.Thread(target=myfunc, args = q)
t.start()
d1=datetime.datetime.utcnow()
while threading.active_count()>1:        
  if (datetime.datetime.utcnow()-d1).total_seconds()>60:
  # if your kill criteria are met, put something in the queue
    q.put(1)

I originally found this answer somewhere online, possibly this. Hope this helps!

Another solution would be to use a separate instance of Python, and monitor the other Python thread, killing it from the system level, with psutils.

Wow, I like the daemon and stealth os._exit solutions too!

Upvotes: 1

Tim Peters
Tim Peters

Reputation: 70582

The docs could be clearer about this. Raising SystemExit tells the interpreter to quit, but "normal" exit processing is still done. Part of normal exit processing is .join()-ing all active non-daemon threads. But your rogue thread never ends, so exit processing waits forever to join it.

As @roippi said, you can do

t.daemon = True

before starting it. Normal exit processing does not wait for daemon threads. Your OS should kill them then when the main process exits.

Another alternative:

import os
os._exit(13)  # whatever exit code you want goes there

That stops the interpreter "immediately", and skips all normal exit processing.

Pick your poison ;-)

Upvotes: 3

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