RFR: 8364103: Convert existing sprintf-chains to stringStream [v4]

[Kim Barrett]

On Mon, 8 Sep 2025 09:47:56 GMT, Paul Hübner <phubner at openjdk.org> wrote:

>> Hi all,
>> 
>> This PR refactors `javaClasses`' `print_stack_element_to_stream` to use a `stringStream` instead of manually maintaining a buffer with `os::snprintf` chains.
>> 
>> The JBS issue outlines to do this for all occurrences of `snprintf`-like chains. The majority of the calls to `os::snprintf`, `os::snprintf_checked`, `os::vsnprintf`, etc. occur just once. `LogTagSet::vwrite` is the only place to my knowledge where there remains a `vsnprintf` chain using manual buffer arithmetic. After consulting @jdksjolen, we decided that due to the
>> a) low-level nature of the code, and 
>> b) widespread usage of logging in the VM, 
>> this should probably warrant a larger discussion and/or separate issue. Personally, I feel like the performance & correctness risks of introducing a high-level abstraction here outweighs the benefits. 
>> 
>> I've run tests with JDK tiers 1-3 on macOS (AArch64, x64), Linux (AArch64, x64), and Windows (x64); all green.
>
> Paul Hübner has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update src/hotspot/share/classfile/javaClasses.cpp
>   
>   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>

Looks even better.

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Marked as reviewed by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26894#pullrequestreview-3198195337