RFR: 8357086: os::xxx functions returning memory size should return size_t [v23]

[David Holmes]

On Fri, 1 Aug 2025 09:19:55 GMT, Anton Artemov <duke at openjdk.org> wrote:

>> Hi,
>> 
>> in this PR the output value types for functions which return memory are changed, namely:
>> 
>> 
>> static julong available_memory(); --> static bool available_memory(size_t& value);
>> static julong used_memory(); --> static bool used_memory(size_t& value);
>> static julong free_memory(); --> static bool free_memory(size_t& value); 
>> static jlong total_swap_space(); --> static bool total_swap_space(size_t& value);
>> static jlong free_swap_space(); --> static bool free_swap_space(size_t& value); 
>> static julong physical_memory(); --> static size_t physical_memory(size_t& value); 
>> 
>> 
>> The return boolean value, where available, indicates success, whereas the actual value is assigned to the input argument. The following recommended usage pattern is introduced: where applicable, and unsuccessful call is logged. 
>> 
>> `ATTRIBUTE_NODISCARD` macro is added as a placeholder for `[[nodiscard]]`, which will be available with C++17.
>> 
>> Tested in GHA and Tiers 1-5.
>
> Anton Artemov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 24 commits:
> 
>  - 8357086: Fixed merge conflict
>  - 8357086: Removed extra line
>  - 8357086: Made physical_memory() return size_t, added dummy ATTRIBUTE_NODISCARD
>  - 8357086: Small fixes
>  - 8357086: Made physical_memory() return void
>  - 8357086: Fixed behavior of total_swap_space on Linux
>  - 8357086: Addressed reviewer's comments.
>  - 8357086: Fixed void conversion.
>  - 8357086: Addressed reviewer's comments
>  - 8357086: Addressed reviewer's comments
>  - ... and 14 more: https://git.openjdk.org/jdk/compare/d80b5c87...f9b2c6d8

src/hotspot/share/runtime/arguments.cpp line 1507:

> 1505: void Arguments::set_heap_size() {
> 1506:   julong phys_mem;
> 1507:   size_t physical_mem_val = 0;

I'm not seeing why you needed to introduce this as a temporary. ??

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PR Review Comment: https://git.openjdk.org/jdk/pull/25450#discussion_r2250670601