RFR: 8336299: Improve GCLocker stall diagnostics

[Neethu Prasad]

On Wed, 24 Jul 2024 08:27:49 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> It might also be nice to give an example of such a new message in the CR.

updated PR summary. 
Examples are as below


1. Last thread exiting. Performing GC after exiting critical section. Thread "main" 0 locked.

2. Thread exiting critical region Thread "main" 0 locked.

3. Thread stalled by JNI critical section. Resumed after 586ms. Thread "Thread-0".

4. Thread blocked to enter critical region. Resumed after 1240ms. Thread "SIGINT handler".

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PR Comment: https://git.openjdk.org/jdk/pull/20277#issuecomment-2264414125