RFR: 8213269: convert test/hotspot/jtreg/runtime/memory/RunUnitTestsConcurrently to gtest [v6]

[Thomas Stuefe]

On Wed, 3 Mar 2021 14:51:24 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Okay so you're right that we can't account in NMT and with our malloc guards for the memory that is allocated with std::vector, so I'm convinced that Misha should change this.  Hopefully we can figure out how to make std::vector work in the future, because Misha's 2 lines for it look quite nice.
>> Do you think using std:: would increase build times? My suspicion is that the Access barrier templates are to blame, but building hotspot is a fraction of building the whole jdk, which does seem to take a long time.
>
> Using the C++ Standard Library has long been, and as yet remains, forbidden in HotSpot code.  In particular, using standard containers hasn't played nicely with HotSpot's native memory tracking.  A small number of uses of standard library facilities has crept into some of the gtests; I think jfr is the only "offender" at present.  That shouldn't have been allowed, and there are some configuration and build kludges that were required to make that work.

> Okay so you're right that we can't account in NMT and with our malloc guards for the memory that is allocated with std::vector, so I'm convinced that Misha should change this. Hopefully we can figure out how to make std::vector work in the future, because Misha's 2 lines for it look quite nice.
> Do you think using std:: would increase build times? My suspicion is that the Access barrier templates are to blame, but building hotspot is a fraction of building the whole jdk, which does seem to take a long time.

Well, yesterday I saw to my annoyance that upgrading from g++-7 to g++-9 increased jdk build time by about 30-40%, so I today I am very aware of build times :-/ But you are right of course, its just the hotspot, so maybe its not such a big deal.

I am a bit apprehensive about introducing STL (had to port the STL to outlier platforms in the past and god that was terrible) but mainly I'd like to have a public discussion before starting to use it. And if the majority thinks its okay then I am okay with it too oc. I have been wrong before. Kim said STL quality is very high nowadays.

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PR: https://git.openjdk.java.net/jdk/pull/2436