Subprocess.popen not creating independent process

Question

I have a piece of code that is in charge of spawning new independent processes (which should live after the main process terminates).

When I run this code using 'run' from PyCharm they do get spawned independently and stay alive even after their parent terminates.

The problem is when running from a cmd shell (in windows), they get spawned but it seems as if they are bound to the spawning shell (Not the python script), so the main script finishes but the shell stays active and once I close it the processes gets terminated.

service_path = "some_service_path"
service_arguments = "some arguments"
python_execution_location = os.path.join(os.environ["PYTHON3_ROOT"], "python.exe")
execution_value = "{} {} {}".format(python_execution_location, service_path, service_arguments)
my_process = subprocess.Popen(execution_value, shell=True)

@Abhineet Why should that change anything? According to the documentation setting shell=true sets the CREATE_NEW_CONSOLE flag to true by default, meaning it should be completley independent. — Rohi, Mar 18 '19 at 06:34
okay, I read about that. Are you trying to run some service code using Python.exe? And when you say, the child terminates, you mean the Python.exe and service, both of them terminates on closing the console, right? — Abhineet, Mar 18 '19 at 06:56
The python scripts are "services" which need to get raised by the main python script (main process). When I close the shell all processes terminate. — Rohi, Mar 18 '19 at 07:00
@Rohi - Does this help? https://stackoverflow.com/questions/32808730/running-python-script-as-a-windows-background-process — Scott Skiles, Mar 20 '19 at 14:38
@ScottSkiles I wasn’t aware of the pythonw.exe so I learned something new. But unfortunately it doesn’t help me because I do want the console to be visible. I just want the spawned processes to not be bound to it. — Rohi, Mar 20 '19 at 21:18
In *PyCharm*, when the main script ends, it also kills the child (which is not what you claim that you're experiencing). On *cmd* it works the same way that you described. So are you talking about Windows services or some processes that must remain running (Windows services also do that :) )? What about their output (and error) streams, do you care what they contain (do you care whether it has a console)? Also, do you need to interact with the "services"? What's your *Python* version? — CristiFati, Mar 26 '19 at 18:44

score 2 · Accepted Answer · answered Mar 22 '19 at 17:41

In windows, you could make use of creationflags option of Popen.

DETACHED_PROCESS = 8 # bit mask taken from the linked doc below
subprocess.Popen(executable, creationflags=DETACHED_PROCESS, close_fds=True)

Which will create a detached process (demon process).

https://learn.microsoft.com/en-us/windows/desktop/ProcThread/process-creation-flags

For console processes, the new process does not inherit its parent's console (the default). The new process can call the AllocConsole function at a later time to create a console. For more information, see Creation of a Console.

Just use `subprocess.DETACHED_PROCESS`. – user136036 Jun 29 '22 at 14:49 — user136036, Jun 29 '22 at 14:49

score 1 · Answer 2 · answered Mar 24 '19 at 17:21

1

You might need to send a creationflags arg to make it a seperate process altogether

subprocess.Popen(executable, creationflags=subprocess.CREATE_NEW_PROCESS_GROUP, close_fds=True)

python.org link

answered Mar 24 '19 at 17:21

Anirudh Panchangam

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Subprocess.popen not creating independent process

2 Answers2