[lxc-devel] attach_wait and threads

[Dorian Eikenberg]

Hi there,

I am currently working on a python script that makes use of the python-lxc library (lxc version is the current git version). I had a timer running that would stop the container if the attach_wait method took to long to return. However the event was not triggered before the attach_wait method returned no matter how long this took.
As far as I know the problem can be fixed by making the Container_attach_and_possibly_wait function in python-lxc/lxc.c GIL-aware. Tested this with the script provided below and it worked fine for me.
Here is a minimal python script which should be able to reproduce the problem given a running container "test":
 
import lxc
import threading


def event():
 print("Hello")


def main():
 container = lxc.Container("test")
 timer = threading.Timer(2, event)
 timer.start()
 container.attach_wait(lxc.attach_run_command, ["/bin/sleep", "7"])
 print("all done")

if __name__ == "__main__":
 main()
 
On my system both prints were executed after approx 7 secs.
After applying the following changes to lcx.c the "Hello" string was printed correctly approx 5 secs ahead of "all done":
 
in Container_attach_and_possibly_wait starting at line 583:

if (wait) {
 Py_BEGIN_ALLOW_THREADS
 ret = lxc_wait_for_pid_status(pid);
 Py_END_ALLOW_THREADS
 (...)
 
I hope this was helpful.
 
Regards,
 
Dorian Eikenberg
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