RFR: 8367993: G1: Speed up ConcurrentMark initialization [v3]

[Leo Korinth]

On Wed, 7 Jan 2026 12:58:43 GMT, Leo Korinth <lkorinth at openjdk.org> wrote:

>> This change moves almost all of the ConcurrentMark initialisation from its constructor to the method `G1ConcurrentMark::fully_initialize()`.  Thus, creation time of the VM can be slightly improved by postponing creation of ConcurrentMark. Most time is saved postponing creation of statistics buffers and threads.
>> 
>> It is not obvious that this is the best solution. I have earlier experimented with lazily allocating statistics buffers _only_. One could also initialise a little bit more eagerly (for example the concurrent mark thread) and maybe get a slightly cleaner change. However IMO it seems better to not have ConcurrentMark "half initiated" with a created mark thread, but un-initialised worker threads.
>> 
>> This change is depending on the integration of https://bugs.openjdk.org/browse/JDK-8373253.
>> 
>> I will be out for vacation, and will be back after new year (and will not answer questions during that time), but I thought I get the pull request out now so that you can have a look.
>
> Leo Korinth has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 564 commits:
> 
>  - Merge branch '8373253' into 8367993
>  - Merge branch 'master' into _8373253
>  - Merge branch 'master' into _8367993
>  - 8366058: Outdated comment in WinCAPISeedGenerator
>    
>    Reviewed-by: mullan
>  - 8357258: x86: Improve receiver type profiling reliability
>    
>    Reviewed-by: kvn, vlivanov
>  - 8373704: Improve "SocketException: Protocol family unavailable" message
>    
>    Reviewed-by: lucy, jpai
>  - 8373722: [TESTBUG] compiler/vectorapi/TestVectorOperationsWithPartialSize.java fails intermittently
>    
>    Reviewed-by: jiefu, jbhateja, erfang, qamai
>  - 8343809: Add requires tag to mark tests that are incompatible with exploded image
>    
>    Reviewed-by: alanb, dholmes
>  - 8374465: Spurious dot in documentation for JVMTI ClassLoad
>    
>    Reviewed-by: kbarrett
>  - 8374317: Change GCM IV size to 12 bytes when encrypting/decrypting TLS session ticket
>    
>    Reviewed-by: djelinski, mpowers, ascarpino
>  - ... and 554 more: https://git.openjdk.org/jdk/compare/2aa8aa4b...28ccbb68

I have tested this with tier1-5 without related failures.

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PR Comment: https://git.openjdk.org/jdk/pull/28723#issuecomment-3784140286