RFR: 8367149: Add ergonomic construction for creating ad-hoc VMErrorCallback

[Albert Mingkun Yang]

On Tue, 9 Sep 2025 06:26:32 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> Add a class OnVMError which uses the VMErrorCallback mechanism which is an ergonomic construction for creating ad-hoc VMErrorCallback which automatically calls the provided invocable f if a VM crash occurs within its lifetime. Can be used to instrument a build for more detailed contextual information gathering. Especially useful when hunting down intermittent bugs, or issues only reproducible in environments where access to a debugger is not readily available. Example use:
> ```C++
>   {
>     // Note the lambda is invoked after an error occurs within this thread,
>     // and during on_error's lifetime. If state prior to the crash is required,
>     // capture a copy of it first.
>     auto important_value = get_the_value();
> 
>     OnVMError on_error([&](outputStream* st) {
>       // Dump the important bits.
>       st->print("Prior value: ");
>       important_value.print_on(st);
>       st->print("During crash: ")
>       get_the_value().print_on(st);
>       // Dump whole the whole state.
>       this->print_on(st);
>     });
> 
>     // Sometimes doing a thing will crash the VM.
>     do_a_thing();
>   }
> 
> 
> C++17 class template argument deduction finally makes these sort of constructions ergonomic to use without the need for auto and helper construction methods.

Minor comments/suggestions on the doc.

src/hotspot/share/utilities/vmError.hpp line 254:

> 252: };
> 253: 
> 254: // Ergonomic construction for creating ad-hoc VMErrorCallback which automatically

Does `Ergonomic construction` have specific meanings in cpp/this context? If not, I wonder if `lightweight` is clearer, as it is less technical.

src/hotspot/share/utilities/vmError.hpp line 278:

> 276: 
> 277:     // Sometimes doing a thing will crash the VM.
> 278:     do_a_thing();

// When VM crashes, the above lambda will be invoked and print relevant info.
might_cause_vm_crash();

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Marked as reviewed by ayang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27159#pullrequestreview-3205163906
PR Review Comment: https://git.openjdk.org/jdk/pull/27159#discussion_r2336080660
PR Review Comment: https://git.openjdk.org/jdk/pull/27159#discussion_r2336064339