We already have JFR JavaMonitorInflate event, which tells when the monitor is inflated. We are missing JavaMonitorDeflate event, which would tell us when the monitor is deflated. This makes it hard to see the monitor lifecycle, and/or estimate the population of currently inflated monitors. I believe we should add JavaMonitorDeflate event. It would also be useful to have the statistics for the number of currently used/deflating monitors. Deflation event alone would require post-processing to investigate this, so it would be good to have the statistics event as well.

This would also replace two of the RT counters that are going away in JDK-8348829.

Monitor deflation is done asynchronously in MonitorDeflationThread, so the additional overhead of recording the deflation events would likely be performance neutral.