ResolvedMethodTableHash.java

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/*
 * @test
 * @bug 8249719
 * @summary ResolvedMethodTable hash function should take method class into account
 * @run main/othervm/manual -Xmx256m -XX:MaxMetaspaceSize=256m ResolvedMethodTableHash 200000
 */

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.List;

// The test generates thousands MethodHandles to the methods of the same name
// and the same signature. This should not take too long, unless Method hash
// function takes only the name and the signature as an input.
public class ResolvedMethodTableHash extends ClassLoader {

    // Generate a MethodHandle for ClassName.m()
    private MethodHandle generate(String className) throws ReflectiveOperationException {
        byte[] buf = new byte[100];
        int size = writeClass(buf, className);
        Class<?> cls = defineClass(null, buf, 0, size);
        return MethodHandles.publicLookup().findStatic(cls, "m", MethodType.methodType(void.class));
    }

    private MethodHandle generateWithSameName() throws ReflectiveOperationException {
        byte[] buf = new byte[100];
        int size = writeClass(buf, "MH$$");
        // use different classloader instances to load the classes with the same name
        Class<?> cls = new ResolvedMethodTableHash().defineClass(null, buf, 0, size);
        return MethodHandles.publicLookup().findStatic(cls, "m", MethodType.methodType(void.class));
    }

    // Produce a class file with the given name and a single method:
    //     public static native void m();
    private int writeClass(byte[] buf, String className) {
        return ByteBuffer.wrap(buf)
                .putInt(0xCAFEBABE)       // magic
                .putInt(50)               // version: 50
                .putShort((short) 7)      // constant_pool_count: 7
                .put((byte) 7).putShort((short) 2)
                .put((byte) 1).putShort((short) className.length()).put(className.getBytes())
                .put((byte) 7).putShort((short) 4)
                .put((byte) 1).putShort((short) 16).put("java/lang/Object".getBytes())
                .put((byte) 1).putShort((short) 1).put("m".getBytes())
                .put((byte) 1).putShort((short) 3).put("()V".getBytes())
                .putShort((short) 0x21)   // access_flags: public super
                .putShort((short) 1)      // this_class: #1
                .putShort((short) 3)      // super_class: #3
                .putShort((short) 0)      // interfaces_count: 0
                .putShort((short) 0)      // fields_count: 0
                .putShort((short) 1)      // methods_count: 1
                .putShort((short) 0x109)  //   access_flags: public static native
                .putShort((short) 5)      //   name_index: #5
                .putShort((short) 6)      //   descriptor_index: #6
                .putShort((short) 0)      //   attributes_count: 0
                .putShort((short) 0)      // attributes_count: 0
                .position();
    }

    public static void main(String[] args) throws Exception {
        ResolvedMethodTableHash generator = new ResolvedMethodTableHash();
        List<MethodHandle> handles = new ArrayList<>();

        int count = args.length > 0 ? Integer.parseInt(args[0]) : 200000;

        for (int i = 0; i < count; i++) {
            // prevents metaspace oom
            if (i % 20 != 0) {
                handles.add(generator.generate("MH$" + i));
            } else {
                handles.add(generator.generateWithSameName());
            }
            if (i % 1000 == 0) {
                System.out.println("Generated " + i + " handles");
            }
        }

        System.out.println("Test passed");
    }
}