CODEWITHSUNDEEP
pythonwindowspython-2.7winapi
Neil C. Obremski
Neil C. Obremski

Reputation: 20334

How to detach Python child process on Windows (without setsid)?

I'm migrating some process code to Windows which worked well on Posix. Very simply put: the code to launch a subprocess and immediately detach will not work because setsid() is not available:

import os, subprocess, sys
p = subprocess.Popen([sys.executable, '-c', "print 'hello'"], preexec_fn=os.setsid)

I can remove the use of setsid but then the child process ends when the parent ends.

My question is how do I achieve the same effect as setsid on Windows so that the child process lifetime is independent of the parent's?

I'd be willing to use a particular Python package if one exists for this sort of thing. I'm already using psutil for example but I didn't see anything in it that could help me.

Upvotes: 4

Views: 3608

Answers (1)

Neil C. Obremski
Neil C. Obremski

Reputation: 20334

RbMn's comment on my question is in fact the answer. There is no need to detach because processes in Windows are always top-level objects. I tried this out with a sleeper task and it worked fine.

However as eryksun pointed out in the comments here, closing the console window WILL cause the child process to terminate. I also had some stability issues with Waitress and Popen on Windows that I think I've worked through by adding the following bit of code which sets some process creation flags and uses close_fds:

if 'nt' == os.name:
     flags = 0
     flags |= 0x00000008  # DETACHED_PROCESS
     flags |= 0x00000200  # CREATE_NEW_PROCESS_GROUP
     flags |= 0x08000000  # CREATE_NO_WINDOW

     pkwargs = {
         'close_fds': True,  # close stdin/stdout/stderr on child
         'creationflags': flags,
     }

 p = subprocess.Popen([sys.executable, '-c', cmd], **pkwargs)

Upvotes: 6

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