refactor: Getting rid of (un)assigningCb

[dorjesinpo]

One more step converging CSL/non-CSL

[bmq-oss-ci]

Build 371 of commit 547f190 has completed with FAILURE

[bmq-oss-ci]

Build 374 of commit f2eb61b has completed with FAILURE

[kaikulimu]

This approach doesn't actually work. Assignment is a different story than unassignment. During first pending assignment, the queue does not exist in ClusterState yet, so qcit won't find anything, and thus won't set anything to k_ASSIGNING.

Lemma: If the queue exists in ClusterState, then it is never in k_ASSIGNING state.

Therefore, we need a separate collection to keep track of k_ASSIGNING queues, and once assignment at ClusterState completes, we need to remove the corresponding entry.

[bmq-oss-ci]

Build 387 of commit ea72c8e has completed with FAILURE

[kaikulimu]

Some notes for myself

• ClusterQueueHelper::onQueueAssigned:

  • Legacy mode: Same observer callback, but skipped due to immediate return
  • FSM mode: Observer callback of ClusterState::assignQueue

• ClusterQueueHelper::onQueueAssigning:

  • Legacy mode: Called during ClusterStateManager::assignQueue, ClusterStateManager::registerQueueInfo, ClusterStateManager::processQueueAssignmentRequest, ClusterStateManager::processQueueAssignmentAdvisory
  • FSM mode: Called during ClusterStateManager::assignQueue, ClusterStateManager::registerQueueInfo, ClusterStateManager::processQueueAssignmentRequest

  Both modes share the same first three codepaths via ClusterUtil
  All above methods eventually forwards to ClusterUtil::assignQueue

• ClusterQueueHelper::onQueueUnassigned:

  • Legacy mode: Same observer callback, but skipped due to immediate return
  • FSM mode: Observer callback of ClusterState::unassignQueue

• ClusterQueueHelper::onQueueUnassigning:

  • Legacy mode: Called during ClusterStateManager::processQueueUnAssignmentAdvisory
  • FSM mode: no-op

  In legacy mode, on the leader, removeQueueRaw is called during ClusterQueueHelper::gcExpiredQueues

Places where ClusterQueueHelper::QueueContextMap d_queues are inserted to:

1. ClusterQueueHelper::onQueueAssigned
2. ClusterQueueHelper::openQueue
3. ClusterQueueHelper::onQueueAssigning

If a brand new queue is being opened, ClusterQueueHelper::openQueue will create a new QueueContext. Then, the queue assignment flow will use this context instead of creating its own.

[kaikulimu]

Reviewing, should be done by Dev 5

[kaikulimu]

Progress update:
Queue unassignment flow has been reviewed.
Now moving on to queue assignment flow.

I have refrained from posting my review, in case my perception on queue unassignment aspects changes after I review queue assignment flow.

[kaikulimu]

Review done. Thanks for the hard work! This part of the code is not easy to navigate.

[bmq-oss-ci]

Build 404 of commit 263600c has completed with FAILURE

[kaikulimu]

lgtm