ealeon ealeon - 2 months ago 31
Python Question

python subprocess.Popen hanging

child = subprocess.Popen(command,
shell=True,
env=environment,
close_fds=True,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT,
bufsize=1,
)

subout = ""
with child.stdout:
for line in iter(child.stdout.readline, b''):
subout += line
logging.info(subout)
rc = child.wait()


some times (intermittently) this hangs forever.
not sure if it hangs on
iter(child.stdout.readline)
or
child.wait()


i
ps -ef
for the process it Popens and that process no longer exists

my guess is that it has do with bufsize so that child.stdout.readline is going on forever but i have no idea how to test it and as this happens intermittently

I could implement alarm but i m not sure if that's appropriate as i cant really tell whether the popen'd process is just slow or hanging

let's assume that either child.stdout.readline or wait() hangs forever, what actions could i take besides alarm ?

NPE NPE
Answer

You're likely hitting the deadlock that's explained in the documentation:

Popen.wait():

Wait for child process to terminate. Set and return returncode attribute.

Warning: This will deadlock when using stdout=PIPE and/or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use communicate() to avoid that.

The solution is to use Popen.communicate().