Comment 24 for bug 1543094

Reviewed: https://review.openstack.org/314810
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=c871a43383e6bd40a358087663267da41b7bf1ec
Submitter: Jenkins
Branch: stable/mitaka

commit c871a43383e6bd40a358087663267da41b7bf1ec
Author: Kevin Benton <email address hidden>
Date: Tue Apr 5 23:06:00 2016 -0700

    Add semaphore to ML2 create_port db operation

    This adds a semaphore scoped to the network ID of a port
    creation in ML2 to ensure that all workers on a single server
    only try to allocate an IP for that network one at a time.

    This will alleviate the deadlock error retry mechanism being
    exceeded due to the related bug. It reduces the number of contenders
    for a single IP allocation from number of workers to number of servers.

    It will unblock the switch to pluggable ipam while the IP allocation
    strategy is being revamped to be less racey.

    Partial-Bug: #1543094
    Change-Id: Ieafdd640777d4654fcd0ebb65ace25c30151c412
    (cherry picked from commit db817a9e39dbed10383cb2c70c0f95d4b1795aec)