This patch is the first one of a series of patches improving how the L3
agents update the router HA state to the Neutron server.
This patch partially reverts the previous patch [1]. When the batch
notifier sends events, it calls the callback method passed during the
initialization, in this case AgentMixin.notify_server. The batch
notifier spawns a new thread in charge of sending the notifications and
then wait the specified "batch_interval" time. If the callback method is
not synchronous with the notify thread execution (what [1] implemented),
the thread can finish while the RPC client is still sending the
HA router states. If another HA state update is received, then both
updates can be executed at the same time. It is possible then that a new
router state can be overwritten with an old one still not sent or
processed.
The batch notifier is refactored, to improve what initally was
implemented [2] and then updated [3]. Currently, each new event thread
can update the "pending_events" list. Then, a new thread is spawned to
process this event list. This thread decouples the current execution
from the calling thread, making the event processing a non-blocking
process.
But with the current implementation, each new process will spawn a new
thread, synchronized with the previous and new ones (using a
synchronized decorator). That means, during the batch interval time, the
system can have as many threads waiting as new events received. Those
threads will end secuentially when the previous threads end the batch
interval sleep time.
Instead of this, this patch receives and enqueue each new event and
allows only one thread to be alive while processing the event list. If
at the end of the processing loop new events are stored, the thread will
process then.
[1] I3f555a0c78fbc02d8214f12b62c37d140bc71da1
[2] I2f8cf261f48bdb632ac0bd643a337290b5297fce
[3] I82f403441564955345f47877151e0c457712dd2f
Partial-Bug: #1837635
Change-Id: I20cfa1cf5281198079f5e0dbf195755abc919581
(cherry picked from commit 8b7d2c8a93)
2d849c6fee