Loopy CallSite (original) (raw)

Remi Forax forax at univ-mlv.fr
Sat Jul 12 14:05:10 UTC 2014

It seems that the JIT is lost with whe there is a loopy callsite and never stabilize (or the steady state is after the program ends).

import java.lang.invoke.MethodHandle; import java.lang.invoke.MethodHandles; import java.lang.invoke.MethodType; import java.lang.invoke.MutableCallSite;

public class Loop { static class LoopyCS extends MutableCallSite { public LoopyCS() { super(MethodType.methodType(void.class, int.class));

   MethodHandle target = dynamicInvoker();
   target = MethodHandles.filterArguments(target, 0, FOO);
   target = MethodHandles.guardWithTest(ZERO,
       target,

MethodHandles.dropArguments(MethodHandles.constant(int.class, 0).asType(MethodType.methodType(void.class)), 0, int.class)); setTarget(target); } }

static final MethodHandle FOO, ZERO; static { try { FOO = MethodHandles.lookup().findStatic(Loop.class, "foo", MethodType.methodType(int.class, int.class)); ZERO = MethodHandles.lookup().findStatic(Loop.class, "zero", MethodType.methodType(boolean.class, int.class)); } catch (NoSuchMethodException | IllegalAccessException e) { throw new AssertionError(e); } }

private static boolean zero(int i) { return i != 0; }

private static int foo(int i) { COUNTER++; return i - 1; }

private static int COUNTER = 0;

public static void main(String[] args) throws Throwable { for(int i=0; i<100_000; i++) { new LoopyCS().getTarget().invokeExact(1_000); } System.out.println(COUNTER); } }

cheers, Rémi

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