RFR: JDK-8281460: Let ObjectMonitor have its own NMT category

[David Holmes]

On Tue, 8 Feb 2022 08:10:05 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> It would be useful to distinguish ObjectMonitor allocations in NMT, as a simple way to both to see the needed footprint as well as the number of allocated monitors.
> 
> Note, this needs [JDK-8281450](https://bugs.openjdk.java.net/browse/JDK-8281450) as a prerequisite.

I think mtSynchronizer was for VM synchronization objects: mutexes, semaphore etc. Not ObjectMonitors. But as always if these conventions are not clearly known then "misuse" can creep in.

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PR: https://git.openjdk.java.net/jdk/pull/7378