MonitorActivity processor generating false inactivity files

MonitorActivity generates false inactivity reports (with big ratio), if the FlowFiles are coming less frequent, than the 2/3 of the configured threshold. This happens only in cluster monitoring scope, where only primary node reports, and only non-primary nodes have FlowFiles to process.

This is because, the processor synchronizes the common state only 3 times within the threshold: 1T/3, 2T/3, 3T/3. If the FlowFile hits the non-primary node between the second (2T/3) and the third sync point (3T/3), then the state from the non-primary node will only be shared with the primary node, when the last sync point comes. And as sync points are relativeley calculated by each node, there is a race condition in terms of which happens first: the primary node reads the common state, or the non-primary node writes the new state. In case of the former, primary node will generate a false indication.

[PRIMARY] - SY0 ---- SY1 ----- SY2 ---- SY3 ---- SY4 ----
                     /         /        /      / ? /
[C STATE] ------X---:---------:--------:-------:X-:------
               /        /        /             /
[SLAVE N] -- FF1 ---- SY1 ---- SY2 -- FF2 -- SY3 --------