Fix stop race in MonitorScheduler.#19161
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gianm merged 1 commit intoapache:masterfrom Mar 16, 2026
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When MonitorScheduler "stop" is called, it in turn calls "removeMonitor". This calls "monitor" on all monitors. The whole process is synchronized on the MonitorScheduler itself, but it is not synchronized with the regularly-scheduled calls to "monitor". It can lead to "monitor" running concurrently with itself, which can lead to unpredictable behavior in metrics emission. One likely effect of this would be to emit metrics twice, due to the common pattern of snapshot -> emit deltas from previous snapshot -> save snapshot. This patch also removes the unused CompoundMonitor.
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When MonitorScheduler "stop" is called, it in turn calls "removeMonitor". This calls "monitor" on all monitors. The whole process is synchronized on the MonitorScheduler itself, but it is not synchronized with the regularly-scheduled calls to "monitor". It can lead to "monitor" running concurrently with itself, which can lead to unpredictable behavior in metrics emission.
One likely effect of this would be to emit metrics twice, due to the common pattern of snapshot -> emit deltas from previous snapshot -> save snapshot.
This patch also removes the unused CompoundMonitor.