So why is this first argument not declared as a MethodHandle?
Thanks - Ioi On 4/9/18 1:00 PM, Attila Szegedi wrote:
invokeExact_MT000_LFL_V is a static method and its first declared argument type is java.lang.Object, not MethodHandle. So aload_0 will load a reference with static type of Object, hence making a checkcast necessary to cast it to a MethodHandle. HTH, Attila.On 2018. Apr 9., at 21:49, Ioi Lam <ioi....@oracle.com> wrote: I am looking at the code generated by MethodHandleNatives.linkMethod: (note the output was edited for brevity) $ cat HelloMH.java import java.lang.invoke.*; public class HelloMH { public static void main(String ...args) throws Throwable { MethodHandles.Lookup lookup = MethodHandles.lookup(); MethodType mt = MethodType.methodType(void.class, float.class); MethodHandle mh = lookup.findStatic(HelloMH.class, "callme", mt); mh.invokeExact(4.0f); } private static void callme(float x) { System.out.println("Hello MH.invoke: " + x); Thread.dumpStack(); } } $ javac HelloMH.java $ java -Djava.lang.invoke.MethodHandle.DUMP_CLASS_FILES=true \ -XX:+UnlockDiagnosticVMOptions -XX:+ShowHiddenFrames -cp . HelloMH [...] Hello MH.invoke: 4.0 java.lang.Exception: Stack trace at java.base/java.lang.Thread.dumpStack(Thread.java:1434) at HelloMH.callme(HelloMH.java:13) at java.base/java.lang.invoke.LambdaForm$DM.invokeStatic_LF_V() at java.base/java.lang.invoke.LambdaForm$MH.invokeExact_MT_LFL_V() at HelloMH.main(HelloMH.java:8) $ javap -c 'DUMP_CLASS_FILES/java/lang/invoke/LambdaForm$MH.class' final class java.lang.invoke.LambdaForm$MH { static void invokeExact_MT000_LFL_V(java.lang.Object, float, java.lang.Object); Code: 0: aload_0 1: checkcast #14 // class java/lang/invoke/MethodHandle 4: dup ... Why is the checkcast necessary here? I thought the verifier would ensure that local#0 must of type MethodHandle. Is this checkcast needed only for reflective invocation of MethodHandle.invokeExact()? Thanks - Ioi _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev_______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
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