RFR: 8371380: [LOOM] The debug agent should avoid enabling VIRTUAL_THREAD_START/END events when possible [v5]

[Serguei Spitsyn]

On Thu, 4 Dec 2025 00:19:25 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Don't enabled VIRTUAL_THREAD_START/END events unless absolutely necessary. Solves performance issues when trying to debug apps that create a lot of virtual threads. Details in first comment.
>> 
>> With these changes the Skynet benchmark no longer shows any slowdown when launching with debugging enabled or when attaching the debugger.
>> 
>> Tested with all tier2, tier3, tier5, and tier6 CI testing (with filters to only run svc tests).
>
> Chris Plummer has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Fixed typo in comment
>  - Add comment for virtualThreadStartEventsEnabledForDeferredEventMode

Looks good.

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Marked as reviewed by sspitsyn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28485#pullrequestreview-3542659993