RFR: 8267341: macos attempt_reserve_memory_at(arg1, arg2, true) failure [v6]

[Gerard Ziemski]

On Mon, 10 Jan 2022 16:21:01 GMT, Gerard Ziemski <gziemski at openjdk.org> wrote:

>> Re-enable **release_multi_mappings** gtest on macOS
>> 
>> This test would occasionally fail on macOS, but thanks to Dan's catch, it turned out that it actually only fails on those test machines that run macOS 10.13.6 or earlier.
>> 
>> The proposed fix simply makes a single call to `os::reserve_memory()` with the `executable` flag `True`, and if that failed forces `executable`  to `False` later in the actual test code (alternatively we could have just also skipped that test portion completely, but this way we actually do something rather than nothing at all).
>> 
>> Tested manually on macOS 10.13.6 and via Mach5
>
> Gerard Ziemski has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add nice comment for the workaround implementation

Thank you David, Dan for the reviews! If you could check this one last time, then maybe I can still push it into jdk18

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PR: https://git.openjdk.java.net/jdk/pull/6960