RFR(S) [15] : 8249000 : vm.gc.X should take selected JIT into account

[Igor Ignatyev]

Hi Vladimir,

thanks for your review!

`vm.gc` and `vm.gc.X`-s are different beasts (and admittedly, they confuse people a lot), `vm.gc` is set to "X", by jtreg itself, only if there is UseXGC in vm flags, otherwise it's "null". `vm.gc.X` are set by VMProps class, and you can have more than one vm.gc.X == true, as vm.gc.X means that X gc is supported by JVM and it can be selected; so if there are no Use.*GC in vm flags, vm.gc.X will yield true for all GCs which JVM was built with; if one of UseXGC is provided, only corresponding vm.gc.X is true, and all others are false. so to answer your questions, yes `vm.gc` can be "null" (if there are no Use.*GC) , and yes `vm.gc.Z & vm.gc.Serial & vm.gc == null` can be true (if there are no Use.*GC and JVM supports both Z and Serial GCs).

Thanks,
-- Igor 


> On Jul 7, 2020, at 8:00 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
> Nice clean up, Igor
> 
> test/hotspot/jtreg/gc/stress/TestReclaimStringsLeaksMemory.java
> 
> Do we even can have vm.gc=="null" based on code in VMProps.java? At least some GC should be selected ergonomically even if non is specified on command line.
> 
> - * @requires vm.gc=="null" & !vm.graal.enabled & !vm.debug
> + * @requires vm.gc == "null"
> + * @requires !vm.debug

> 
> 
> test/hotspot/jtreg/runtime/cds/appcds/TestZGCWithCDS.java
> 
> Does next combination of @requires ever work? I thought such sequence means 'AND' operation on all such conditions.
> 
>  * @requires vm.gc.Z
>  * @requires vm.gc.Serial
>  * @requires vm.gc == null
> 
> 
> Thanks,
> Vladimir
> 
> On 7/7/20 5:38 PM, Igor Ignatyev wrote:
>> http://cr.openjdk.java.net/~iignatyev/8249000/webrev.00/
>>> 241 lines changed: 34 ins; 5 del; 202 mod;
>> Hi all,
>> could you please review the patch which modifies requires/VMProps to set vm.gc.X to false if Graal is selected and X GC isn't supported by Graal?
>> the patch also replaces @requires similar to `vm.gc.X & !vm.graal.enabled` w/ `vm.gc.X` where it's applicable.
>> from JBS:
>>> not all GCs are supported by Graal JIT, which leads to failures like JDK-8247527 and boilerplate fixes like replacing all `@requires vm.gc.Z` w/ `@requires vm.gc.Z & !vm.graal.enabled`.
>>> 
>>> as vm.gc.X means that X GC can be selected, it would be more natural, less surprising, and much more clear to have it true if the selected JIT supports the said X GC.
>> webrev: http://cr.openjdk.java.net/~iignatyev/8249000/webrev.00/
>> JBS: https://bugs.openjdk.java.net/browse/JDK-8249000
>> testing: test/hotspot/jtreg/{gc,compiler,runtime,serviceability} on {linux,windows,macos}-x64 w/ and w/o Graal as JIT
>> Thanks,
>> -- Igor