(10) RFR (actually S) 8169881: Remove implicit Handle conversions oop->Handle (original) (raw)

David Holmes david.holmes at oracle.com
Tue Feb 14 01:44:31 UTC 2017

Hi Coleen,

"actually S"? :)

On 14/02/2017 6:10 AM, Coleen Phillimore wrote:

Summary: Pass THREAD to Handle as argument instead of implicit Thread::current() call.

Well there's a bit more to it than that as you also change parameter types so that we (sometimes) avoid:

across method calls. This leads to some puzzling differences eg:

src/share/vm/aot/aotCodeHeap.cpp src/share/vm/classfile/javaClasses.hpp

The change in aotCodeHeap.cpp reverses the use of Handle and oop, but it is unclear why Throwable::print and Throwable::print_stack_trace have different signatures in that regard. They used to both take a Handle but now one takes an oop instead. ??

More generally it is unclear why you made the changes you did in places

I understand why the oop to Handle implicit conversion could be problematic due to the Thread::current() calls, but I don't understand why you couldn't keep (? add?) the Handle to oop implicit conversions ??

src/share/vm/c1/c1_Runtime1.cpp

Aside: I'm a little surprised that there was not a Handle assignment operator or copy constructor such that given:

863 Handle appendix(THREAD, NULL); 970 appendix = cpce->appendix_if_resolved(pool);

that it simply updated the NULL to the desired value, while keeping the THREAD intact.

src/share/vm/ci/ciInstance.cpp

Not at all obvious that replacing Handle with raw oop is correct. I'm not saying it isn't, just that it isn't obvious - and I'll wonder why the Handle was used in the first place.

src/share/vm/classfile/javaClasses.cpp

Why change java_lang_String::as_symbol_or_null to take a Handle instead of an oop if you are simply going to unwrap the Handle to get the oop back. ??? Particular when a caller like src/share/vm/prims/methodHandles.cpp has to create the Handle from oop in the first place.

src/share/vm/jvmci/jvmciCompilerToVM.hpp

It is not at all obvious that JavaArgumentUnboxers are thread-confined! I'm also concerned by API's (unfortunately a number pre-existing) that take a Thread/JavaThread argument but really require it to be the current thread. To that end I'd rather see _thread as _cur_thread and an assertion when it is set.

src/share/vm/oops/cpCache.cpp

Nit: objArrayHandle resolved_references (Thread::current(), ...

Please remove space before (

src/share/vm/prims/jvm.cpp

Nit: need to fix indent on StackWalk::walk call second line.

src/share/vm/prims/jvmtiGetLoadedClasses.cpp

Ditto re _thread -> _cur_thread

src/share/vm/prims/jvmtiImpl.cpp

Nit: space before ( again (on handle constructor)

It's a very small change to a number of files. Notably the new JVMCI files have a lot of implicit conversions from oop to handle. I want to get this change in early for jdk10 to stop this usage. I also added a few HandleMarks where I found that the HandlesArea was growing large.

The addition and removal of the HandleMarks seems problematic because there are no obvious rules being applied. It is hard to know where and when a HandleMark is needed or not. Looking at src/share/vm/jvmci/jvmciCompilerToVM.cpp do we really want to create/destroy the HandleMark on each loop iteration? That would only seem necessary if we know the number of iterations is so high that we might consume all our handle space.

Thanks, David

See bug for more on the motivation of this change.

open webrev at http://cr.openjdk.java.net/~coleenp/8169881.01/webrev bug link https://bugs.openjdk.java.net/browse/JDK-8169881 Tested by running all hotspot jtreg tests with -XX:+CheckUnhandledOops. There weren't any unhandled oops amazingly. Thanks, Coleen

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