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

Coleen Phillimore coleen.phillimore at oracle.com
Wed Feb 20 12:27:22 PST 2013

On 2/20/2013 3:21 PM, John Rose wrote:

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

On 2/20/2013 2:51 PM, John Rose wrote: On Feb 20, 2013, at 10:20 AM, Coleen Phillimore <coleen.phillimore at oracle.com <mailto:coleen.phillimore at oracle.com>> wrote:

Summary: Add JVMCONSTANTPseudoString in place of JVMCONSTANTObject 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 JVMCONSTANTPseudoString. 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 sethaspseudostring. 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 hasinvokedynamic for that matter. haspreresolution 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.

Awesome.

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 "CONSTANTPLACEHOLDER42" (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.

Okay, it would probably be done with patching and never recover the string constant.

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 JVMCONSTANTPseudoString (and the constant for Object can be removed too). Won't we need a tag that says "this thing is a patched constant"? JVMCONSTANTPatched?

If I null out the Symbol* value in JVM_CONSTANT_String, I won't need a special constant pool constant. I missed some places to add JVM_CONSTANT_PseudoString in my edit (as you noticed with loadable_constant). I hate this extra constant.

I want to revert to the original change (to null out the Symbol* to indicate it's patched), and add the Object tag and flags cleanup.

Thanks for the info how this works. I'll send out another webrev later.

Coleen

— John

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