RFR: 8295376: Improve debug agent virtual thread performance when no debugger is attached

[Serguei Spitsyn]

On Fri, 28 Oct 2022 01:47:44 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Thank you for explanation.
>> Moving it inside critical section makes it more safe and clean.
>
> BTW, I also eventually realized that the `waiting_for_active_callbacks` flag is not really even necessary. What is does is save having to do an unnecessary notify each time `active_callbacks` goes back to 0. Instead it only does the notify when it goes to 0 AND we are shutting down the debugger connection. So it does help with performance a little, but I'm not sure if it is even noticeable.

Agreed. I'm for getting rid of this variable and simplifying the code.

-------------

PR: https://git.openjdk.org/jdk/pull/10865