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PERFORMANCE: Intern Multiple String Constants #4754



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@original-brownbear original-brownbear commented Aug 27, 2017

JRuby interns most Strings that come up in Ruby code just fine in

    public String decodeString() {
        int strLength = decodeInt();

        if (strLength == NULL_STRING) return null;

        byte[] bytes = new byte[strLength]; // FIXME: This seems really innefficient

        String newString = new String(bytes).intern();

        if (RubyInstanceConfig.IR_READING_DEBUG) System.out.println("STR<" + newString + ">");

        return newString;

, but a few duplicates from more dynamic contexts are not caught. In the red-black benchmark, this adds up to ~200kb of wasted memory (memory wise this is irrelevant obviously, but duplicates make call site cache lookups slower and waste CPU cache => fixing all these spots resulted in a visible ~2% speedup in the red-black benchmark for me over very large sample sizes 2k+ runs).

So I:

  • Tracked down spots generating duplicate constants for ASTish code paths
  • Did my best to not introduce duplicate calls to intern by interning in constructors wherever possible instead of further upstream
  • Made sure not intern calls made it into the hot path by checking that the method isn't called in the hot path (checked red-black benchmark and Logstash after warm up and intern was never called in either => I have a bit of confidence)


  • Removed public synchronized void defineAliases(List<String> aliases, String oldName) since it was one of the cases that looked like they would create duplicate String constants but then realized that it's never used (checked for dynamic invocations too)
  • Reduced visibility of public static JavaCallable getMatchingCallable(Ruby runtime, Class<?> javaClass, String methodName, Class<?>[] argumentTypes) since this method was in a path affected by the added intern calls and only used privately => I didn't want to add redundant calls to intern to it, when I can be sure that its only caller interns Strings just fine already
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@original-brownbear original-brownbear commented Aug 27, 2017

this is not ready, closing until fixed ...

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@enebo enebo commented Aug 28, 2017

@original-brownbear also check out symbol_love which is a branch which will be eliminating any String's from existing. Everything will be RubySymbol and we will have backwards compat signatures for people interacting via Java. That branch is not a sure thing for the future but j.l.String needs to go since it limits our compatibility with non-Java-charset encodings.

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@original-brownbear original-brownbear commented Aug 28, 2017

@enebo thanks will take a look :)

@enebo enebo added this to the JRuby milestone Sep 6, 2017
@enebo enebo added this to the JRuby milestone Sep 6, 2017
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2 participants