RFR: 8333047: Remove arena-size-workaround in jvmtiUtils.cpp

[Thomas Stuefe]

On Tue, 28 May 2024 12:36:41 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> In `JvmtiUtil::single_threaded_resource_area()`, we create a resource area that is supposed to work even if the current thread is not attached yet and there is no associated Thread or the Thread has no valid ResourceArea.
> 
> It contains a workaround:
> 
> 
>     // lazily create the single threaded resource area
>     // pick a size which is not a standard since the pools don't exist yet
>     _single_threaded_resource_area = new (mtInternal) ResourceArea(Chunk::non_pool_size);
> 
> 
> It specifies a non-standard chunk size to circumvent the chunk-pool-based allocation in the RA constructor, ensuring that only malloc is used. This is because in the old days the ChunkPools had been allocated from C-Heap and there was a time window when no chunk pools were live yet.
> 
> This is quirky and a bit ugly. It is also unnecessary since [JDK-8272112](https://bugs.openjdk.org/browse/JDK-8272112) (since JDK 18). We now create chunk pools as global objects, so they are live as soon as the libjvm C++ initialization ran. We can remove this workaround and the comment.
> 
> ---
> 
> Tests: GHAs.
> I also manually called this function, and allocated from the resulting ResourceArea, at the very beginning of CreateJavaVM. I made sure that both allocations and follow-up-chunk-allocation worked even this early in VM life.

@jdksjolen could you take a look? You know the Arena coding behind it, and this PR is, in a very circumvent way, one of the prerequisites for NMT simplifications I plan.

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PR Comment: https://git.openjdk.org/jdk/pull/19425#issuecomment-2135835425