RFR: 8373839: Disable JVM TI suspension during JNI critical regions

[Patricio Chilano Mateo]

On Thu, 18 Dec 2025 01:24:42 GMT, David Holmes <dholmes at openjdk.org> wrote:

> To ensure JNI critical access to a raw array can't interfere with actions of the debugger, we disable JVM TI suspension whilst JNI critical access is active, as originally suggested by @fisk. We assume the debugger is being operated correctly (ie the thread using the raw array will be suspended), and that the critical section is short so as to not delay debugging too long. 
> 
> The mechanism for this already exists courtesy of the virtual thread support.
> 
> Testing:
>  - tiers 1 - 6 sanity

So this `_is_disable_suspend` flag will prevent the target from processing the async handshake and suspend, but the suspender will still consider the target suspended once `SuspendThreadHandshakeClosure` is done. We would need to check the state of the target and don't consider it "handshake safe" if it's in a JNI critical region.

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PR Comment: https://git.openjdk.org/jdk/pull/28884#issuecomment-3671897422