RFR: 8357086: os::xxx functions returning memory size should return size_t [v26]

[Anton Artemov]

> 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: Addressed reviewer's comments

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25450/files
  - new: https://git.openjdk.org/jdk/pull/25450/files/fbceea99..f9d9bc4a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25450&range=25
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25450&range=24-25

  Stats: 16 lines in 2 files changed: 2 ins; 3 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/25450.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25450/head:pull/25450

PR: https://git.openjdk.org/jdk/pull/25450