_Example.java

package net.burningtnt.javatest.dmh;

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

public final class Example {
    private static final MethodHandleLinker<Runnable> LINKER = new MethodHandleLinker<>(Runnable.class, "run", MethodType.methodType(void.class));

    public static void main(String[] args) throws Throwable {
        Runnable runnable = LINKER.of(MethodHandles.lookup().findStatic(
                Example.class, "run", MethodType.methodType(void.class)
        ));

        runnable.run();
    }

    private static void run() {
        System.out.println("run1");
    }
}

MethodHandleLinker.java

/*
 * MethodHandleLinker

 * Copyright (c) 2024 Burning_TNT<[email protected]>

 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:

 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package net.burningtnt.javatest.dmh;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Array;
import java.lang.reflect.Field;

public final class MethodHandleLinker<T> {
    private static final String DMH_CLASS = MethodHandleLinker.class.getName().replace('.', '/');
    private static final String IMPL_CLASS = DMH_CLASS + "$LinkerImpl";

    private static final ThreadLocal<MethodHandle> PENDING_MH = new ThreadLocal<>();

    @SuppressWarnings("unused")
    private static MethodHandle getMH() {
        MethodHandle mh = PENDING_MH.get();
        PENDING_MH.remove();
        return mh;
    }

    private static final MethodHandle CLASS_DEFINER = locateClassDefiner();

    @SuppressWarnings("all")
    private static MethodHandle locateClassDefiner() {
        MethodHandles.Lookup LOOKUP = MethodHandles.lookup();

        Exception e1;
        try {
            Class<?> clazz = Class.forName("sun.misc.Unsafe");
            MethodHandle mh = LOOKUP.findVirtual(clazz, "defineAnonymousClass", MethodType.methodType(Class.class, Class.class, byte[].class, Object[].class));

            Field f = clazz.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            return MethodHandles.insertArguments(MethodHandles.insertArguments(mh, 0, f.get(null), MethodHandleLinker.class), 1, (Object) null);
        } catch (Exception e) {
            e1 = e;
        }

        try {
            Class<?> classOptionClass = Class.forName("java.lang.invoke.MethodHandles$Lookup$ClassOption");

            Object[] options = (Object[]) Array.newInstance(classOptionClass, 1);
            options[0] = classOptionClass.getField("NESTMATE").get(null);

            MethodHandle mh = LOOKUP.findVirtual(MethodHandles.Lookup.class, "defineHiddenClass", MethodType.methodType(MethodHandles.Lookup.class, byte[].class, boolean.class, options.getClass()));

            return MethodHandles.filterReturnValue(MethodHandles.insertArguments(mh.bindTo(LOOKUP), 1, false, options), LOOKUP.findVirtual(MethodHandles.Lookup.class, "lookupClass", MethodType.methodType(Class.class)));
        } catch (Exception e2) {
            IllegalStateException e = new IllegalStateException("Cannot initialize CLASS_DEFINER");
            e.addSuppressed(e1);
            e.addSuppressed(e2);
            throw e;
        }
    }

    private enum VMStackType {
        OBJECT(Opcodes.ALOAD, Opcodes.ARETURN, 1),
        NUMBER(Opcodes.ILOAD, Opcodes.IRETURN, 1),
        FLOAT(Opcodes.FLOAD, Opcodes.FRETURN, 1),
        DOUBLE(Opcodes.DLOAD, Opcodes.DRETURN, 2),
        LONG(Opcodes.LLOAD, Opcodes.LRETURN, 2),
        VOID(-1, Opcodes.RETURN, 0);

        private final int loadingOpcode, returnOpcode, stackWidth;

        VMStackType(int loadingOpcode, int returnOpcode, int stackWidth) {
            this.loadingOpcode = loadingOpcode;
            this.returnOpcode = returnOpcode;
            this.stackWidth = stackWidth;
        }

        public static VMStackType of(Class<?> clazz) {
            if (!clazz.isPrimitive()) {
                return OBJECT;
            } else if (clazz == int.class || clazz == short.class || clazz == char.class || clazz == byte.class || clazz == boolean.class) {
                return NUMBER;
            } else if (clazz == float.class) {
                return FLOAT;
            } else if (clazz == double.class) {
                return DOUBLE;
            } else if (clazz == long.class) {
                return LONG;
            } else {
                return VOID;
            }
        }
    }

    private final byte[] classBytes;

    public MethodHandleLinker(Class<T> interfaceClass, String methodName, MethodType methodType) {
        ClassWriter cw = new ClassWriter(0);
        cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL, IMPL_CLASS, null, "java/lang/Object", new String[]{
                interfaceClass.getName().replace('.', '/')
        });
        {
            FieldVisitor fv = cw.visitField(Opcodes.ACC_PRIVATE | Opcodes.ACC_STATIC | Opcodes.ACC_FINAL, "MH", "Ljava/lang/invoke/MethodHandle;", null, null);
            fv.visitEnd();
        }
        {
            MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC | Opcodes.ACC_STATIC, "<clinit>", "()V", null, null);
            mv.visitCode();
            mv.visitMethodInsn(Opcodes.INVOKESTATIC, DMH_CLASS, "getMH", "()Ljava/lang/invoke/MethodHandle;", false);
            mv.visitFieldInsn(Opcodes.PUTSTATIC, IMPL_CLASS, "MH", "Ljava/lang/invoke/MethodHandle;");
            mv.visitInsn(Opcodes.RETURN);
            mv.visitMaxs(1, 0);
            mv.visitEnd();
        }
        {
            MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
            mv.visitCode();
            mv.visitVarInsn(Opcodes.ALOAD, 0);
            mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
            mv.visitInsn(Opcodes.RETURN);
            mv.visitMaxs(1, 1);
            mv.visitEnd();
        }
        {
            String methodDesc = methodType.toMethodDescriptorString();
            MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, methodName, methodDesc, null, null);
            mv.visitCode();
            mv.visitFieldInsn(Opcodes.GETSTATIC, IMPL_CLASS, "MH", "Ljava/lang/invoke/MethodHandle;");

            int stackMAX = 1, l = methodType.parameterCount();
            for (int i = 0; i < l; i++) {
                VMStackType type = VMStackType.of(methodType.parameterType(i));
                if (type == VMStackType.VOID) {
                    throw new AssertionError("Parameters should NOT be void.");
                }
                mv.visitVarInsn(type.loadingOpcode, stackMAX);
                stackMAX += type.stackWidth;
            }

            mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/invoke/MethodHandle", "invokeExact", methodDesc, false);

            VMStackType type = VMStackType.of(methodType.returnType());
            mv.visitInsn(type.returnOpcode);

            stackMAX = Math.max(stackMAX, 1 + type.stackWidth);
            mv.visitMaxs(stackMAX, stackMAX);
            mv.visitEnd();
        }
        cw.visitEnd();

        classBytes = cw.toByteArray();
    }

    @SuppressWarnings("unchecked")
    public T buildBinding(MethodHandle mh) {
        try {
            PENDING_MH.set(mh);
            return (T) ((Class<?>) CLASS_DEFINER.invokeExact(classBytes)).getConstructor().newInstance();
        } catch (Throwable e) {
            throw new IllegalArgumentException("Cannot define the linker.", e);
        }
    }
}