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https://issues.apache.org/jira/browse/NIFI-16383?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Pierre Villard updated NIFI-16383:
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Status: Patch Available (was: Open)
> Make FlowController node connection state access lock-free
> ----------------------------------------------------------
>
> Key: NIFI-16383
> URL: https://issues.apache.org/jira/browse/NIFI-16383
> Project: Apache NiFi
> Issue Type: Improvement
> Reporter: Pierre Villard
> Assignee: Pierre Villard
> Priority: Major
>
> *FlowController#getNodeConnectionState()* currently acquires the
> FlowController read lock before reading the local node connection status.
> This can cause a circular wait during startup flow synchronization:
> # FlowController#synchronize() holds the write lock while loading the flow.
> # Controller Services are enabled on lifecycle threads, while the
> synchronization thread waits for enablement.
> # A Controller Service can call NodeTypeProvider#getNodeConnectionState()
> from customValidate().
> # FlowController#getNodeConnectionState() then waits for the read lock,
> which cannot be acquired while synchronization holds the write lock.
> # Synchronization waits for validation, and validation waits for
> synchronization to release the lock.
> This reproduces the same class of 30-second Controller Service enablement
> stall addressed for isClustered() by NIFI-16153.
> The lock is not required for memory visibility:
> * configuredForClustering is final.
> * connectionStatus is volatile.
> * NodeConnectionStatus is immutable.
> Update FlowController#getNodeConnectionState() to read these fields without
> acquiring the FlowController read lock. Preserve the existing return
> semantics:
> * Return STANDALONE when clustering is not configured.
> * Return DISCONNECTED when clustering is configured but no local status is
> available.
> * Otherwise map the local framework connection state to the API
> NodeConnectionState.
> Add focused coverage proving that the accessor:
> * Returns the correct state without taking the FlowController read lock.
> * Can be called from Controller Service validation while flow
> synchronization holds the write lock.
> * Does not block Controller Service enablement or cause the synchronization
> timeout.
> This change allows components to use
> NodeTypeProvider#getNodeConnectionState() during startup validation to defer
> decisions while the node is CONNECTING, without reintroducing the
> flow-synchronization lock inversion.
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