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  1. JDK
  2. JDK-8057846

ClassVerifier::change_sig_to_verificationType temporary symbol creation code is hot

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    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 9
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
    • Resolved In Build:
      b35
    • Verification:
      Not verified

      Backports

        Description

        If one runs a classloader benchmark:
          http://cr.openjdk.java.net/~shade/8053904/benchmarks.jar

        ...with Nashorn-generated class files:
         http://cr.openjdk.java.net/~shade/8053904/classes.jar

        ...and jdk9 executed as:
         $ java -jar benchmarks.jar -wi 0 -i 30 -r 10s -p file=classes.jar

        ...one can produce this profile:
         http://cr.openjdk.java.net/~shade/8053904/class-install-calltree-2.txt

        Looking closely at this profile, one can note an interesting thing: ClassVerifier::change_sig_to_verificationType seems to spend a lot of time creating the temporary symbols:

         ClassVerifier::change_sig_to_verificationType seems to copy the symbols a lot:
          +- 30.740 (9%) ClassVerifier::change_sig_to_verificationType(SignatureStream*,VerificationType*,Thread*)
          | +- 15.070 (4%) SignatureStream::as_symbol(Thread*)
          | +- 14.850 (4%) ClassVerifier::create_temporary_symbol(const Symbol*,int,int,Thread*)

        This seems to be an offending piece of code:

        inline int ClassVerifier::change_sig_to_verificationType(
            SignatureStream* sig_type, VerificationType* inference_type, TRAPS) {
          BasicType bt = sig_type->type();
          switch (bt) {
            case T_OBJECT:
            case T_ARRAY:
              {
                Symbol* name = sig_type->as_symbol(CHECK_0);
                // Create another symbol to save as signature stream unreferences
                // this symbol.
                Symbol* name_copy =
                  create_temporary_symbol(name, 0, name->utf8_length(), CHECK_0);
                assert(name_copy == name, "symbols don't match");
                *inference_type =
                  VerificationType::reference_type(name_copy);
                return 1;
              }

        ...and it comes from a mammoth changeset:

        $ hg log -r 2062
        changeset: 2062:3582bf76420e
        user: coleenp
        date: Thu Jan 27 16:11:27 2011 -0800
        summary: 6990754: Use native memory and reference counting to implement SymbolTable
         
        I think we need to reconsider how we manage symbol lifecycle to evade unreferencing without doing a copy.

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                Assignee:
                coleenp Coleen Phillimore
                Reporter:
                shade Aleksey Shipilev
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