Review-Request: Fix of JDK-8034775 neglects to account for non-JIT VMs

[Severin Gehwolf]

Hi David,

On Tue, 2014-04-29 at 20:07 +1000, David Holmes wrote:
> On 28/04/2014 9:42 PM, Severin Gehwolf wrote:
> > Hi,
> >
> > Bug: JI-9011998 (I don't seem to be able to create JDK bugs)
> > Webrev: http://jerboaa.fedorapeople.org/bugs/openjdk/JI-9011998/v1/
> >
> > The fix for JDK-8034775 introduced a start-up check requiring the number
> > of compiler threads to be >= 1, which does not make sense for non-JIT
> > VMs such as the zero JVM variant. This causes zero JVMs to fail
> > initialization with:
> >
> > CICompilerCount of 0 is invalid; must be at least 1
> > Error: Could not create the Java Virtual Machine.
> > Error: A fatal exception has occurred. Program will exit.
> >
> > This is caused by a wrong start-up check in
> > src/share/vm/runtime/arguments.cpp where a minimal value of 1 is
> > required no matter the JVM variant.
> >
> > The proposed fix uses the defined CI_COMPILER_COUNT pre-processor
> > constant over a static 1 to pass to verify_min_value(). Since
> > CI_COMPILER_COUNT is going to be defined differently for JVM variants it
> > will make the lower water mark check correct for all JVM variants.
> >
> > There was an error in defining CI_COMPILER_COUNT as well. On line 196 in
> > src/share/vm/runtime/globals.hpp CI_COMPILER_COUNT is defined to be 0
> > (since COMPILER1, COMPILER2 and SHARK are not defined for a Zero build.
> > Then on line 201 in src/share/vm/runtime/globals.hpp the "else" branch
> > of ifdef COMPILER2 is entered and the earlier definition of
> > CI_COMPILER_COUNT (with value 0) overridden to 1.
> 
> I don't see that. There are nested if-else branches:

Doh! Yes, you are right. Good catch!

>   167 #if !defined(COMPILER1) && !defined(COMPILER2) && !defined(SHARK)
>   ...
>   196     #define CI_COMPILER_COUNT 0
>   197 #else

That's the else I've missed :(

>   198
>   199     #ifdef COMPILER2
>   200         #define CI_COMPILER_COUNT 2
>   201     #else
>   202         #define CI_COMPILER_COUNT 1
>   203     #endif // COMPILER2
>   204
>   205 #endif // no compilers

Updated webrev removing the changes to src/share/vm/runtime/globals.hpp:
http://jerboaa.fedorapeople.org/bugs/openjdk/JI-9011998/v2/

As to why the if on line 167 is entered I'm still unsure. Apparently one
of COMPILER1, COMPILER2, SHARK is defined for a --with-jvm-variants=zero
build. It's not apparent to me which it is and why :-/

config.log has this and the build machine is F20:
configure --enable-option-checking=fatal
--with-boot-jdk=/usr/lib/jvm/java-1.8.0-openjdk.x86_64
--with-debug-level=slowdebug --disable-zip-debug-info
--enable-unlimited-crypto --with-zlib=system --with-giflib=system
--with-stdc++lib=dynamic --with-num-cores=8 --with-jvm-variants=zero

More thoughts?

Cheers,
Severin

> > I've amended test/compiler/startup/NumCompilerThreadsCheck.java so as to
> > verify that the lower water mark for Zero JVMs is 0.
> >
> > Thoughts?
> >
> > Cheers,
> > Severin
> >