RFR: 8267341: macos attempt_reserve_memory_at(arg1, arg2, true) failure [v5]

[Daniel D.Daugherty]

On Fri, 7 Jan 2022 15:46:56 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:
> 
>   avoid impl details in the comment, reword slightly

Marked as reviewed by dcubed (Reviewer).

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