ControllerEventManager

ControllerEventManager manages the event queue (of QueuedEvents) and the controller-event-thread for event processing.

ControllerEventManager allows for emitting ControllerEvents (with optional preempting the queue first).

ControllerEventManager is created exclusively for the KafkaController (when started up).

When started, ControllerEventManager simply requests the ControllerEventThread to start processing ControllerEvents.

ControllerEventManager is started when KafkaController is started up.

Figure 1. ControllerEventManager is Created and Started With KafkaController

ControllerEventManager is in one of the possible ControllerStates.

Note	The state of `ControllerEventManager` is exactly the state of the owning KafkaController.

Creating ControllerEventManager Instance

ControllerEventManager takes the following to be created:

Controller ID (i.e. the broker.id of the broker)
ControllerEventProcessor
Time
KafkaTimers per ControllerState (Map[ControllerState, KafkaTimer])

ControllerEventManager initializes the internal properties.

Performance Metrics

ControllerEventManager is a KafkaMetricsGroup with the following performance metrics.

Table 1. ControllerEventManager’s Performance Metrics
Metric Name	Description
`EventQueueTimeMs`
`EventQueueSize`	Number of QueuedEvents in the event queue

The performance metrics are registered in kafka.controller:type=ControllerEventManager group.

Figure 2. Partition in jconsole

Emitting (Enqueuing) Controller Event — `put` Method

put(event: ControllerEvent): QueuedEvent

put creates a new QueuedEvent with the ControllerEvent and adds it at the end of the event queue.

Note	`put` is used when: `ControllerBrokerRequestBatch` is requested to sendEvent `ControllerEventManager` is requested to clearAndPut `KafkaController` is requested to do its operation and emits various events

Starting ControllerEventManager (and ControllerEventThread) — `start` Method

start(): Unit

start simply requests the ControllerEventThread to start processing ControllerEvents.

Note	`ControllerEventThread` is a `ShutdownableThread` that triggers `doWork()` method when started.

Note	`start` is used exclusively when `KafkaController` is requested to start up (when `KafkaServer` is requested to start).

`clearAndPut` Method

clearAndPut(
  event: ControllerEvent): QueuedEvent

clearAndPut…FIXME

Note	`clearAndPut` is used when: `ControllerEventManager` is requested to close (and emit a `ShutdownEventThread` event) `KafkaController` is requested to startup (and registers a `StateChangeHandler` that emits an `Expire` event when `beforeInitializingSession`)

Closing Up — `close` Method

close(): Unit

close simply clears the event queue and emits a ShutdownEventThread event.

In the end, close waits until the shutdown is complete. You should see the following INFO message in the logs:

Shutdown completed

Note	`close` is used exclusively when `KafkaController` is requested to shutdown.

Internal Properties

Name Description

Name	Description
`queue`	Event queue of QueuedEvents (`LinkedBlockingQueue[QueuedEvent]`) that is a Java java.util.concurrent.LinkedBlockingQueue (i.e. an optionally-bounded blocking queue based on linked nodes that orders elements in first-in-first-out fashion)
`_state`	ControllerState: Idle when `ControllerEventManager` is created and right after `ControllerEventThread` has finished processing a controller event State transitions happen per the requested state of the `ControllerEvent` being processed (while `ControllerEventThread` is processing controller events)
`thread`	ControllerEventThread with controller-event-thread thread name

queue

Event queue of QueuedEvents (LinkedBlockingQueue[QueuedEvent]) that is a Java java.util.concurrent.LinkedBlockingQueue (i.e. an optionally-bounded blocking queue based on linked nodes that orders elements in first-in-first-out fashion)

_state

ControllerState:

Idle when ControllerEventManager is created and right after ControllerEventThread has finished processing a controller event
State transitions happen per the requested state of the ControllerEvent being processed (while ControllerEventThread is processing controller events)

thread

ControllerEventThread with controller-event-thread thread name

ControllerEventManager