[jdk21u-dev] RFR: 8340547: Starting many threads can delay safepoints [v4]

[Sergey Nazarkin]

On Fri, 1 Aug 2025 16:14:19 GMT, Sergey Nazarkin <snazarki at openjdk.org> wrote:

>> I'd like to backport this fix to fix the issue with starting a lot of threads in a burst. Some users found this to be a barrier to migrating from JDK8. 
>> 
>> The backport is not clean as required to adjust `globals.hpp` and replace `ConditionalMutexLocker` with classic `MutexLocker`. Original fix and discussion are [here](https://github.com/openjdk/jdk/pull/21111)
>> 
>> Tested with `tier1` and reproducers from [JDK-8340547](https://bugs.openjdk.org/browse/JDK-8340547), [JDK-8307970](https://bugs.openjdk.org/browse/JDK-8307970)
>
> Sergey Nazarkin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add extra space to outline new option

The `linux-cross-compile` failures are unrelated; they are PPC64LE and S390X stuck on sysroot creation.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/1365#issuecomment-3150000542