RFR (L, tedious again, sorry) 8189610: Reconcile jvm.h and all jvm_md.h between java.base and hotspot

coleen.phillimore at oracle.com coleen.phillimore at oracle.com
Mon Oct 30 12:07:46 UTC 2017

On 10/28/17 3:46 AM, David Holmes wrote:
> On 28/10/2017 3:47 AM, mandy chung wrote:
>> On 10/27/17 7:08 AM, coleen.phillimore at oracle.com wrote:
>>> On 10/27/17 9:37 AM, David Holmes wrote:
>>>> The one file that is needed is a hotspot file - jvm.h defines the 
>>>> interface that hotspot exports via jvm.cpp.
>>>> If you leave jvm.h in hotspot/prims then a very large chunk of your 
>>>> boilerplate changes are not needed. The JDK code doesn't care what 
>>>> the name of the directory is - whatever it is just gets added as a 
>>>> -I directive (the JDK code will include "jvm.h" not "prims/jvm.h" 
>>>> the way hotspot sources do.
>>>> This isn't something we want to change back or move again later. 
>>>> Whatever we do now we live with.
>>> I think it belongs with jni.h and I think the core libraries group 
>>> would agree.   It seems more natural there than buried in the 
>>> hotspot prims directory.  I guess this is on hold while we have this 
>>> debate.   Sigh.
>>> Actually with -I directives, changing to jvm.h from prims/jvm.h 
>>> would still work.   Maybe we should change the name to jvm.hpp since 
>>> it's jvm.cpp though?   Or maybe just have two divergent copies and 
>>> close this as WNF. 
>> I also think hotspot/prims is not a good location. 
>> src/java.base/share/include is a well-defined location for native 
>> header files.  Maybe internal header files could be placed in 
>> include/internal but this is a separate issue .  I should create an 
>> issue for jvm.h and jmm.h (I looked at the files under the include 
>> directory and jvm.h and jmm.h are the only two internal header files 
>> in the include directory).
> Keeping it in prims avoids the need to touch many hotspot files, and 
> with no changes needed on the JDK side because we use a -I directive 
> to set the include path anyway. This is the exported VM interface so 
> it makes sense to me for it to be located in the VM sources.
> But I'm not going to oppose this either way so it's up to Coleen.

I've already disagreed that this file belongs in 
src/hotspot/share/prims, so the include directive without prims is 
preferred.  This allows putting jvm.h in a new place if/when that is 
agreed upon.
>> I do think removing the duplicated copy of jvm.h is a good change. 
>> This is finally possible with the consolidated repository and we no 
>> longer need to update two copies of jvm.h for any change to the JVM 
> Unfortunately we did not do this though - hence the divergence between 
> the two. The use of int versus long for jint is causing a real problem.
> Coleen also hit the other issue on the head. The JNI and JVM 
> interfaces are C interfaces, not C++. The JDK code that uses them is 
> compiled as C - so all good. But the JVM code that implements them is 
> compiled as C++, and that is why we are getting issues with differing 
> linkage directives.

Well, there is now one source file for jvm.h and jni.h and their machine 
dependent counterparts and 2500 lines of duplicated code is removed with 
this change.  The issues with jint and linkages are resolved and tested 
as well with this changeset.

> David
> -----
>> interface.   This change will work with -I directive setting to the 
>> new location, if changed later.
>> What do you think?
>> Mandy

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