Native threads (tpool.execute) not working on child process

[Gorka Eguileor]

When the parent process used eventlet tpool to run code in native threads then anything the child tries to run in a native thread will hang forever.

The reason for that is that the parent has initialize the pool of threads and use a flag to mark that it has been initialized, and when the child is forked then it will have the flag saying that it has been initialized and expects the threads to be running, but they are not. So there is no thread to pick up the job when a greenlet queues the job, so the greenthread waits forever to get the result of the operation.

After forking the child needs to tell eventlet's tpool that it is not really initialized.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/oslo.service/+/852450

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.service/+/852450
Committed: https://opendev.org/openstack/oslo.service/commit/67daa4b3c21b4030a965cc8dd106adafc418b70e
Submitter: "Zuul (22348)"
Branch: master

commit 67daa4b3c21b4030a965cc8dd106adafc418b70e
Author: Gorka Eguileor <email address hidden>
Date: Mon Aug 8 17:50:53 2022 +0200

    Fix native threads on child process

    When the parent process used eventlet tpool to run code in native
    threads then anything the child tries to run in a native thread will
    hang forever.

    The reason for that is that the parent has initialize the pool of
    threads and use a flag to mark that it has been initialized, and when
    the child is forked then it will have the flag saying that it has been
    initialized and expects the threads to be running, but they are not. So
    there is no thread to pick up the job when a greenlet queues the job, so
    the greenthread waits forever to get the result of the operation.

    This patch tells eventlet's tpool to clean things up on the child just
    after forking, that way if the child uses native threads tpool will
    spawn all the threads again.

    Closes-Bug: #1983949
    Change-Id: If2421427c48faa976d6c6ee9bafe4d563288037b

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.service 3.3.0 release.