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

[Johan Sjölen]

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.

Today, the ChunkPools are allocated before main through static initialization. That means that the ChunkPools exists when main starts executing, so this is safe.

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Marked as reviewed by jsjolen (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19425#pullrequestreview-2084558186