Request for review: 8000797: NPG: is_pseudo_string_at() doesn't work

John Rose john.r.rose at
Wed Feb 20 12:21:56 PST 2013

On Feb 20, 2013, at 11:59 AM, Coleen Phillimore <coleen.phillimore at> wrote:

> On 2/20/2013 2:51 PM, John Rose wrote:
>> On Feb 20, 2013, at 10:20 AM, Coleen Phillimore <coleen.phillimore at> wrote:
>>> Summary: Add JVM_CONSTANT_PseudoString in place of JVM_CONSTANT_Object and use this tag to distinguish patched pseudo strings. The original string is retained if it was present.
>> This is reasonable; it is a good cleanup.  If you can propose a name better than "PseudoString" I'm all ears.
> If the string is really meaningless, maybe it can be deleted and we don't need this JVM_CONSTANT_PseudoString.  The only reason I kept "String" in the name is because I thought the string would have some meaning to be preserved.

The string is meaningless.  It is just a waste of UTF8 symbol table space.

>> Consider getting rid of set_has_pseudo_string.  That flag was present (IIRC) only to tell the GC that there might be non-perm oops in the constant pool.  Do we still need that?
> I'd be happy to.  I noticed it wasn't being used.   Neither is _has_invokedynamic for that matter.   _has_preresolution does do something.

Not any more.  That flag was added for the sake of the internally-generated bytecodes:
changeset:   2522:ddd894528dbc
user:        jrose
date:        Thu Jun 23 17:14:06 2011 -0700
summary:     7056328: JSR 292 invocation sometimes fails in adapters for types not on boot class path

It appears that we can get rid of all those flags.

>>> I'm not sure how class file reconstitution for pseudo-strings is going to work, but I thought it was prudent to leave the Symbol* in the slot for the patched string.
>> If you really wanted to reconstitute a class file for an anonymous class, and if that class has oop patching (pseudo-strings), you would need either to (a) reconstitute the patches array handed to Unsafe.defineAnonymousClass, or (b) accept whatever odd strings were there first, as an approximation.  The "odd strings" are totally insignificant, and are typically something like "CONSTANT_PLACEHOLDER_42" (see InvokerBytecodeGenerator::constantPlaceholder).
> Maybe there isn't a way or API to reconstitute an anonymous class.   I don't know if there is.

If reconstituting a class means recovering the parameters originally passed to defineClass, then anonymous classes with patching are inherently a special case.  I wouldn't worry about it too much.

> I'm not sure how to reconstitute a normal class in the first place.   Maybe Serguei can comment.   If this class cannot be reconsitituted, I'll change this to remove the string in the patched case and won't need JVM_CONSTANT_PseudoString (and the constant for Object can be removed too).

Won't we need a tag that says "this thing is a patched constant"?  JVM_CONSTANT_Patched?

— John
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