RFR: 8357086: os::xxx functions returning memory size should return size_t [v34]

[David Holmes]

On Thu, 21 Aug 2025 12:30:40 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, an 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 incrementally with one additional commit since the last revision:
> 
>   8357086: Fixed method name in assert in os_windows.cpp
>   
>   Co-authored-by: Stefan Karlsson <stefan.karlsson at oracle.com>

One comment below but otherwise I think everything I have been concerned about has been addressed. Thanks for your patience.

src/hotspot/share/utilities/globalDefinitions.hpp line 60:

> 58: 
> 59: // Dummy placeholder for use of [[nodiscard]]
> 60: #define ATTRIBUTE_NODISCARD

I think you can just use `[[nodiscard]]` directly now. We are going to allow it and the guide is just going through the official update process.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25450#pullrequestreview-3153982860
PR Review Comment: https://git.openjdk.org/jdk/pull/25450#discussion_r2299817113