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Editorial Team
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Asked: 2026-05-20T20:58:45+00:00

I’m sure I’m missing something simple, but when using the subprocess module, there is

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I’m sure I’m missing something simple, but when using the subprocess module, there is a very significant wait (> 10 seconds) to starting the first subprocess. The second one starts shortly after the first. Is there any way to fix this? Code below:

EDIT: To add, HWAccess (in proc.py) links a dll. Could this have anything to do with it?
EDIT2: I’ve boiled the test down to starting a SINGLE subprocess and it takes significantly longer to import HWAccess than if I just run proc.py directly from cmd prompt. I don’t see how this has anything to do with the dll specifically if it loads fast from cmd, but not as a sub-process through test.py

test.py: 

import subprocess
import os
import time

print 'STARTING'
proc0 = subprocess.Popen(['python','proc.py','0'])
proc1 = subprocess.Popen(['python','proc.py','1'])

while True: 
    try: pass
    except KeyboardInterrupt: 
    os._exit(0)
except ValueError: 
    pass

proc.py: 

print 'Process starting...'
import HWAccess
print 'HWAccess imported...'
import sys
print 'sys imported...'
import time
print 'time imported...'

print 'hi from ',sys.argv[1]

Edit: After putting the prints in, there is around 5s to reach the first ‘Process starting…’, the second process prints ‘Process starting…’ immediately afterwards. Then there is a ~30 second pause to import HWAccess (takes a matter of seconds running on an individual process), the second process then immediately prints that it too has imported HWAccess… from then on execution is fast. HWAccess links a .dll so I’m wondering if two processes trying to import HWAccess result in some sort of race condition that takes a while to negotiate.

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1 Answer

  1. Editorial Team

    I am not sure if this is the right track, but I remember seeing such delays when starting a process wayyy back (and not at all Python related), and it turned out they were related to some badly configured network settings on my computer. Upon subprocess start-up, it has to set up interprocess communication, and those settings might interfere.

    I remember my problems were related to using a false hostname for the machine, which was not properly configured on the network – can you check to see if it is your case? If it is not a production machine, try not setting a hostname at all, leaving it as “localhost”.

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