[openstack-dev] [Oslo][Neutron] Fork() safety and oslo.messaging

Ken Giusti kgiusti at gmail.com
Mon Nov 24 19:27:22 UTC 2014

Hi all,

As far as oslo.messaging is concerned, should it be possible for the
main application to safely os.fork() when there is already an active
connection to a messaging broker?

I ask because I'm hitting what appears to be fork-related issues with
the new AMQP 1.0 driver.  I think the same problems have been seen
with the older impl_qpid driver as well [0]

Both drivers utilize a background threading.Thread that handles all
async socket I/O and protocol timers.

In the particular case I'm trying to debug, rpc_workers is set to 4 in
neutron.conf.  As far as I can tell, this causes neutron.service to
os.fork() four workers, but does so after it has created a listener
(and therefore a connection to the broker).

This results in multiple processes all select()'ing the same set of
networks sockets, and stuff breaks :(

Even without the background process, wouldn't this use still result in
sockets being shared across the parent/child processes?   Seems


[0] https://bugs.launchpad.net/oslo.messaging/+bug/1330199

Ken Giusti  (kgiusti at gmail.com)

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