Comment 7 for bug 1548190

Reviewed: https://review.openstack.org/452623
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=37de2f6c4c831a8f4515eee9938996936dd2776c
Submitter: Jenkins
Branch: stable/newton

commit 37de2f6c4c831a8f4515eee9938996936dd2776c
Author: Kevin Benton <email address hidden>
Date: Fri Nov 18 04:25:32 2016 -0700

    Lock in DHCP agent based on network_id

    All cache operations and dnsmasq process operations
    are scoped to a network ID so we can always safely
    perform concurrent actions on different network IDs.
    This patch adjusts the DHCP agent to lock based on
    network ID rather than having a global lock for every
    operation.

    sync_state calls are still protected with a reader/writer
    lock to ensure that when sync_state needs to run, all
    other operations are blocked.

    Related-Bug: #1548190
    Change-Id: I56010dc801d82be56f12e834c5164316872c2f8b
    (cherry picked from commit d1930cefd27448eefc373a229a26f8da25581983)

    Squashed this this commit since tests fail otherwise:

    Always acquire network.id lock in dhcp port update

    Looking at the cache before aqcuiring a lock may cause the
    agent to mistakenly think the network doesn't exist when it
    is actually being wired in parallel.

    Always acquiring the network-based semaphore will ensure that
    the network isn't currently being setup in another coroutine.

    Closes-Bug: #1659919
    Change-Id: I99ae71e3c5b1cd91dca3f6c80b04d2ecb79de64f
    (cherry picked from commit 38de22bf2d4c0879a84db4fbc9fa030f181affc0)