Mark Payne created NIFI-16495:
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Summary: ProcessSession can silently drop or overwrite state
updates when another writer changes state
Key: NIFI-16495
URL: https://issues.apache.org/jira/browse/NIFI-16495
Project: Apache NiFi
Issue Type: Bug
Components: Core Framework
Reporter: Mark Payne
Assignee: Mark Payne
When a {{ProcessSession}} commits a state update made with {{setState}},
{{clearState}}, or {{replaceState}}, {{StandardProcessSession}} reads the
stored state, compares its version with the version the session assigned to its
own update, and calls {{setState}} only if the two differ. This compares
against the wrong version. If another writer stores state exactly once after
the session read it, the versions match and the session's update is silently
dropped. If the other writer stores state more than once, the session
overwrites it. The read and the write are also separate calls, so another
writer can store state between them.
The session should keep the {{StateMap}} it read before building its update
and, on commit, call {{StateManager.replace}} with that {{StateMap}}. That
stores the update only if no other writer changed the state since the session
read it, as the {{ProcessSession.setState}} JavaDoc describes, and does so in
one call instead of two. Each State Provider's {{replace}} must accept the
{{StateMap}} instance the session received.
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