RFR 8245289: Clean up offset code in JavaClasses

[David Holmes]

Hi Coleen,

On 28/05/2020 10:48 pm, coleen.phillimore at oracle.com wrote:
> Summary: Make offset member names consistent and private, move static 
> initializations near owning classes
> 
> This one is better.  I gave up on the X macros because they didn't save 
> typing.  The changes here were to add underscores to offset field names, 
> remove _in_bytes for offset accessors and add asserts that the offset is 
> non-zero, made java_lang_ref_Reference offset fields private, and moved 
> static member definitions closer to the class instead of some random 
> place in javaClasses.cpp.

I focused on the javaClasses.* changes rather than the incidental 
changes due to the _in_bytes removal.

src/hotspot/share/classfile/javaClasses.hpp

  892   static void serialize_offsets(SerializeClosure* f) NOT_CDS_RETURN;

You dropped the NOT_CDS_RETURN in the new code.

---

src/hotspot/share/classfile/javaClasses.inline.hpp

I'm confused about the removal of the initialization assertions. I would 
have expected this, for example,

  33 void java_lang_String::set_coder(oop string, jbyte coder) {
  34   string->byte_field_put(_coder_offset, coder);

to be expressed using coder_offset():

  33 void java_lang_String::set_coder(oop string, jbyte coder) {
  34   string->byte_field_put(coder_offset(), coder);

so that we still get an initialization check. Though I see that 
initialization checks are an area where there remains a lot of 
inconsistency - it's not clear when we can rely solely on the "_x_offset 
!= 0" check versus the "_initialized==true" check, and there are many 
methods with no initialization check at all.

Thanks,
David
-----

> See discussion for 8243996 Remove hardcoded field offsets for more 
> details. 
> https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-May/041732.html
> 
> Tested with tier1-6.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/2020/8245289.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8245289
> 
> Thanks,
> Coleen