VarHandles.java

/*
 * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.lang.invoke;

import jdk.internal.value.NullRestrictedCheckedType;
import jdk.internal.value.ValueClass;
import jdk.internal.vm.annotation.LooselyConsistentValue;
import sun.invoke.util.Wrapper;

import java.lang.foreign.MemoryLayout;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.nio.ByteOrder;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Stream;

import static java.lang.invoke.MethodHandleStatics.UNSAFE;
import static java.lang.invoke.MethodHandleStatics.VAR_HANDLE_SEGMENT_FORCE_EXACT;
import static java.lang.invoke.MethodHandleStatics.VAR_HANDLE_IDENTITY_ADAPT;
import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;

final class VarHandles {

    static VarHandle makeFieldHandle(MemberName f, Class<?> refc, boolean isWriteAllowedOnFinalFields) {
        if (!f.isStatic()) {
            long foffset = MethodHandleNatives.objectFieldOffset(f);
            Class<?> type = f.getFieldType();
            if (!type.isPrimitive()) {
                if (type.isValue()) {
                    int layout = f.getLayout();
                    boolean isAtomic = isAtomicFlat(f);
                    boolean isFlat = f.isFlat();
                    if (isFlat) {
                        if (isAtomic) {
                            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                                    ? new VarHandleFlatValues.FieldInstanceReadOnly(refc, foffset, type, f.getCheckedFieldType(), layout)
                                    : new VarHandleFlatValues.FieldInstanceReadWrite(refc, foffset, type, f.getCheckedFieldType(), layout));
                        } else {
                            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                                    ? new VarHandleNonAtomicFlatValues.FieldInstanceReadOnly(refc, foffset, type, f.getCheckedFieldType(), layout)
                                    : new VarHandleNonAtomicFlatValues.FieldInstanceReadWrite(refc, foffset, type, f.getCheckedFieldType(), layout));
                        }
                    } else {
                        if (isAtomic) {
                            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                                    ? new VarHandleReferences.FieldInstanceReadOnly(refc, foffset, type, f.getCheckedFieldType())
                                    : new VarHandleReferences.FieldInstanceReadWrite(refc, foffset, type, f.getCheckedFieldType()));
                        } else {
                            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                                    ? new VarHandleNonAtomicReferences.FieldInstanceReadOnly(refc, foffset, type, f.getCheckedFieldType())
                                    : new VarHandleNonAtomicReferences.FieldInstanceReadWrite(refc, foffset, type, f.getCheckedFieldType()));
                        }
                    }
                } else {
                    return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleReferences.FieldInstanceReadOnly(refc, foffset, type, f.getCheckedFieldType())
                       : new VarHandleReferences.FieldInstanceReadWrite(refc, foffset, type, f.getCheckedFieldType()));
                }
            }
            else if (type == boolean.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleBooleans.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleBooleans.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == byte.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleBytes.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleBytes.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == short.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleShorts.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleShorts.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == char.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleChars.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleChars.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == int.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleInts.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleInts.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == long.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleLongs.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleLongs.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == float.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleFloats.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleFloats.FieldInstanceReadWrite(refc, foffset));
            }
            else if (type == double.class) {
                return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                       ? new VarHandleDoubles.FieldInstanceReadOnly(refc, foffset)
                       : new VarHandleDoubles.FieldInstanceReadWrite(refc, foffset));
            }
            else {
                throw new UnsupportedOperationException();
            }
        }
        else {
            Class<?> decl = f.getDeclaringClass();
            var vh = makeStaticFieldVarHandle(decl, f, isWriteAllowedOnFinalFields);
            return maybeAdapt(UNSAFE.shouldBeInitialized(decl)
                    ? new LazyInitializingVarHandle(vh, decl)
                    : vh);
        }
    }

    static VarHandle makeStaticFieldVarHandle(Class<?> decl, MemberName f, boolean isWriteAllowedOnFinalFields) {
        Object base = MethodHandleNatives.staticFieldBase(f);
        long foffset = MethodHandleNatives.staticFieldOffset(f);
        Class<?> type = f.getFieldType();
        if (!type.isPrimitive()) {
            assert !f.isFlat() : ("static field is flat in " + decl + "." + f.getName());
            if (type.isValue()) {
                if (isAtomicFlat(f)) {
                    return f.isFinal() && !isWriteAllowedOnFinalFields
                            ? new VarHandleReferences.FieldStaticReadOnly(decl, base, foffset, type, f.getCheckedFieldType())
                            : new VarHandleReferences.FieldStaticReadWrite(decl, base, foffset, type, f.getCheckedFieldType());
                } else {
                    return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                            ? new VarHandleNonAtomicReferences.FieldStaticReadOnly(decl, base, foffset, type, f.getCheckedFieldType())
                            : new VarHandleNonAtomicReferences.FieldStaticReadWrite(decl, base, foffset, type, f.getCheckedFieldType()));
                }
            } else {
                return f.isFinal() && !isWriteAllowedOnFinalFields
                        ? new VarHandleReferences.FieldStaticReadOnly(decl, base, foffset, type, f.getCheckedFieldType())
                        : new VarHandleReferences.FieldStaticReadWrite(decl, base, foffset, type, f.getCheckedFieldType());
            }
        }
        else if (type == boolean.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleBooleans.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleBooleans.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == byte.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleBytes.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleBytes.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == short.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleShorts.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleShorts.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == char.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleChars.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleChars.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == int.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleInts.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleInts.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == long.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleLongs.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleLongs.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == float.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleFloats.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleFloats.FieldStaticReadWrite(decl, base, foffset));
        }
        else if (type == double.class) {
            return maybeAdapt(f.isFinal() && !isWriteAllowedOnFinalFields
                    ? new VarHandleDoubles.FieldStaticReadOnly(decl, base, foffset)
                    : new VarHandleDoubles.FieldStaticReadWrite(decl, base, foffset));
        }
        else {
            throw new UnsupportedOperationException();
        }
    }

    static boolean isAtomicFlat(MemberName field) {
        boolean hasAtomicAccess = (field.getModifiers() & Modifier.VOLATILE) != 0 ||
                !(field.getCheckedFieldType() instanceof NullRestrictedCheckedType) ||
                !field.getFieldType().isAnnotationPresent(LooselyConsistentValue.class);
        return hasAtomicAccess && !HAS_OOPS.get(field.getFieldType());
    }

    static boolean isAtomicFlat(Object[] array) {
        Class<?> componentType = array.getClass().componentType();
        boolean hasAtomicAccess = ValueClass.isAtomicArray(array) ||
                !ValueClass.isNullRestrictedArray(array) ||
                !componentType.isAnnotationPresent(LooselyConsistentValue.class);
        return hasAtomicAccess && !HAS_OOPS.get(componentType);
    }

    static final ClassValue<Boolean> HAS_OOPS = new ClassValue<>() {
        @Override
        protected Boolean computeValue(Class<?> c) {
            for (Field f : c.getDeclaredFields()) {
                Class<?> ftype = f.getType();
                if (UNSAFE.isFlatField(f) && HAS_OOPS.get(ftype)) {
                    return true;
                } else if (!ftype.isPrimitive()) {
                    return true;
                }
            }
            return false;
        }
    };

    // Required by instance field handles
    static Field getFieldFromReceiverAndOffset(Class<?> receiverType,
                                               long offset,
                                               Class<?> fieldType) {
        for (Field f : receiverType.getDeclaredFields()) {
            if (Modifier.isStatic(f.getModifiers())) continue;

            if (offset == UNSAFE.objectFieldOffset(f)) {
                assert f.getType() == fieldType;
                return f;
            }
        }
        throw new InternalError("Field not found at offset");
    }

    // Required by instance static field handles
    static Field getStaticFieldFromBaseAndOffset(Class<?> declaringClass,
                                                 long offset,
                                                 Class<?> fieldType) {
        for (Field f : declaringClass.getDeclaredFields()) {
            if (!Modifier.isStatic(f.getModifiers())) continue;

            if (offset == UNSAFE.staticFieldOffset(f)) {
                assert f.getType() == fieldType;
                return f;
            }
        }
        throw new InternalError("Static field not found at offset");
    }

    // This is invoked by non-flat array var handle code when attempting to access a flat array
    public static void checkAtomicFlatArray(Object[] array) {
        if (!isAtomicFlat(array)) {
            throw new IllegalArgumentException("Attempt to perform a non-plain access on a non-atomic array");
        }
    }

    static VarHandle makeArrayElementHandle(Class<?> arrayClass) {
        if (!arrayClass.isArray())
            throw new IllegalArgumentException("not an array: " + arrayClass);

        Class<?> componentType = arrayClass.getComponentType();

        int aoffset = (int) UNSAFE.arrayBaseOffset(arrayClass);
        int ascale = UNSAFE.arrayIndexScale(arrayClass);
        int ashift = 31 - Integer.numberOfLeadingZeros(ascale);

        if (!componentType.isPrimitive()) {
            // Here we always return a reference array element var handle. This is because
            // the access semantics is determined at runtime, when an actual array object is passed
            // to the var handle. The var handle implementation will switch to use flat access
            // primitives if it sees a flat array.
            return maybeAdapt(new VarHandleReferences.Array(aoffset, ashift, arrayClass));
        }
        else if (componentType == boolean.class) {
            return maybeAdapt(new VarHandleBooleans.Array(aoffset, ashift));
        }
        else if (componentType == byte.class) {
            return maybeAdapt(new VarHandleBytes.Array(aoffset, ashift));
        }
        else if (componentType == short.class) {
            return maybeAdapt(new VarHandleShorts.Array(aoffset, ashift));
        }
        else if (componentType == char.class) {
            return maybeAdapt(new VarHandleChars.Array(aoffset, ashift));
        }
        else if (componentType == int.class) {
            return maybeAdapt(new VarHandleInts.Array(aoffset, ashift));
        }
        else if (componentType == long.class) {
            return maybeAdapt(new VarHandleLongs.Array(aoffset, ashift));
        }
        else if (componentType == float.class) {
            return maybeAdapt(new VarHandleFloats.Array(aoffset, ashift));
        }
        else if (componentType == double.class) {
            return maybeAdapt(new VarHandleDoubles.Array(aoffset, ashift));
        }
        else {
            throw new UnsupportedOperationException();
        }
    }

    static VarHandle byteArrayViewHandle(Class<?> viewArrayClass,
                                         boolean be) {
        if (!viewArrayClass.isArray())
            throw new IllegalArgumentException("not an array: " + viewArrayClass);

        Class<?> viewComponentType = viewArrayClass.getComponentType();

        if (viewComponentType == long.class) {
            return maybeAdapt(new VarHandleByteArrayAsLongs.ArrayHandle(be));
        }
        else if (viewComponentType == int.class) {
            return maybeAdapt(new VarHandleByteArrayAsInts.ArrayHandle(be));
        }
        else if (viewComponentType == short.class) {
            return maybeAdapt(new VarHandleByteArrayAsShorts.ArrayHandle(be));
        }
        else if (viewComponentType == char.class) {
            return maybeAdapt(new VarHandleByteArrayAsChars.ArrayHandle(be));
        }
        else if (viewComponentType == double.class) {
            return maybeAdapt(new VarHandleByteArrayAsDoubles.ArrayHandle(be));
        }
        else if (viewComponentType == float.class) {
            return maybeAdapt(new VarHandleByteArrayAsFloats.ArrayHandle(be));
        }

        throw new UnsupportedOperationException();
    }

    static VarHandle makeByteBufferViewHandle(Class<?> viewArrayClass,
                                              boolean be) {
        if (!viewArrayClass.isArray())
            throw new IllegalArgumentException("not an array: " + viewArrayClass);

        Class<?> viewComponentType = viewArrayClass.getComponentType();

        if (viewComponentType == long.class) {
            return maybeAdapt(new VarHandleByteArrayAsLongs.ByteBufferHandle(be));
        }
        else if (viewComponentType == int.class) {
            return maybeAdapt(new VarHandleByteArrayAsInts.ByteBufferHandle(be));
        }
        else if (viewComponentType == short.class) {
            return maybeAdapt(new VarHandleByteArrayAsShorts.ByteBufferHandle(be));
        }
        else if (viewComponentType == char.class) {
            return maybeAdapt(new VarHandleByteArrayAsChars.ByteBufferHandle(be));
        }
        else if (viewComponentType == double.class) {
            return maybeAdapt(new VarHandleByteArrayAsDoubles.ByteBufferHandle(be));
        }
        else if (viewComponentType == float.class) {
            return maybeAdapt(new VarHandleByteArrayAsFloats.ByteBufferHandle(be));
        }

        throw new UnsupportedOperationException();
    }

    /**
     * Creates a memory segment view var handle accessing a {@code carrier} element. It has access coordinates
     * {@code (MS, long)} if {@code constantOffset}, {@code (MS, long, (validated) long)} otherwise.
     * <p>
     * The resulting var handle will take a memory segment as first argument (the segment to be dereferenced),
     * and a {@code long} as second argument (the offset into the segment). Both arguments are checked.
     * <p>
     * If {@code constantOffset == false}, the resulting var handle will take a third pre-validated additional
     * offset instead of the given fixed {@code offset}, and caller must ensure that passed additional offset,
     * either to the handle (such as computing through method handles) or as fixed {@code offset} here, is valid.
     *
     * @param carrier the Java carrier type of the element
     * @param enclosing the enclosing layout to perform bound and alignment checks against
     * @param alignmentMask alignment of this accessed element in the enclosing layout
     * @param constantOffset if access path has a constant offset value, i.e. it has no strides
     * @param offset the offset value, if the offset is constant
     * @param byteOrder the byte order
     * @return the created var handle
     */
    static VarHandle memorySegmentViewHandle(Class<?> carrier, MemoryLayout enclosing, long alignmentMask,
                                             boolean constantOffset, long offset, ByteOrder byteOrder) {
        if (!carrier.isPrimitive() || carrier == void.class) {
            throw new IllegalArgumentException("Invalid carrier: " + carrier.getName());
        }
        boolean be = byteOrder == ByteOrder.BIG_ENDIAN;
        boolean exact = VAR_HANDLE_SEGMENT_FORCE_EXACT;

        // All carrier types must persist across MethodType erasure
        VarForm form;
        if (carrier == byte.class) {
            form = VarHandleSegmentAsBytes.selectForm(alignmentMask, constantOffset);
        } else if (carrier == char.class) {
            form = VarHandleSegmentAsChars.selectForm(alignmentMask, constantOffset);
        } else if (carrier == short.class) {
            form = VarHandleSegmentAsShorts.selectForm(alignmentMask, constantOffset);
        } else if (carrier == int.class) {
            form = VarHandleSegmentAsInts.selectForm(alignmentMask, constantOffset);
        } else if (carrier == float.class) {
            form = VarHandleSegmentAsFloats.selectForm(alignmentMask, constantOffset);
        } else if (carrier == long.class) {
            form = VarHandleSegmentAsLongs.selectForm(alignmentMask, constantOffset);
        } else if (carrier == double.class) {
            form = VarHandleSegmentAsDoubles.selectForm(alignmentMask, constantOffset);
        } else if (carrier == boolean.class) {
            form = VarHandleSegmentAsBooleans.selectForm(alignmentMask, constantOffset);
        } else {
            throw new IllegalStateException("Cannot get here");
        }

        return maybeAdapt(new SegmentVarHandle(form, be, enclosing, offset, exact));
    }

    private static VarHandle maybeAdapt(VarHandle target) {
        if (!VAR_HANDLE_IDENTITY_ADAPT) return target;
        target = filterValue(target,
                        MethodHandles.identity(target.varType()), MethodHandles.identity(target.varType()));
        MethodType mtype = target.accessModeType(VarHandle.AccessMode.GET);
        for (int i = 0 ; i < mtype.parameterCount() ; i++) {
            target = filterCoordinates(target, i, MethodHandles.identity(mtype.parameterType(i)));
        }
        return target;
    }

    public static VarHandle filterValue(VarHandle target, MethodHandle pFilterToTarget, MethodHandle pFilterFromTarget) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(pFilterToTarget);
        Objects.requireNonNull(pFilterFromTarget);
        //check that from/to filters do not throw checked exceptions
        MethodHandle filterToTarget = adaptForCheckedExceptions(pFilterToTarget);
        MethodHandle filterFromTarget = adaptForCheckedExceptions(pFilterFromTarget);

        List<Class<?>> newCoordinates = new ArrayList<>();
        List<Class<?>> additionalCoordinates = new ArrayList<>();
        newCoordinates.addAll(target.coordinateTypes());

        //check that from/to filters have right signatures
        if (filterFromTarget.type().parameterCount() != filterToTarget.type().parameterCount()) {
            throw newIllegalArgumentException("filterFromTarget and filterToTarget have different arity", filterFromTarget.type(), filterToTarget.type());
        } else if (filterFromTarget.type().parameterCount() < 1) {
            throw newIllegalArgumentException("filterFromTarget filter type has wrong arity", filterFromTarget.type());
        } else if (filterToTarget.type().parameterCount() < 1) {
            throw newIllegalArgumentException("filterToTarget filter type has wrong arity", filterFromTarget.type());
        } else if (filterFromTarget.type().lastParameterType() != filterToTarget.type().returnType() ||
                filterToTarget.type().lastParameterType() != filterFromTarget.type().returnType()) {
            throw newIllegalArgumentException("filterFromTarget and filterToTarget filter types do not match", filterFromTarget.type(), filterToTarget.type());
        } else if (target.varType() != filterFromTarget.type().lastParameterType()) {
            throw newIllegalArgumentException("filterFromTarget filter type does not match target var handle type", filterFromTarget.type(), target.varType());
        } else if (target.varType() != filterToTarget.type().returnType()) {
            throw newIllegalArgumentException("filterFromTarget filter type does not match target var handle type", filterToTarget.type(), target.varType());
        } else if (filterFromTarget.type().parameterCount() > 1) {
            for (int i = 0 ; i < filterFromTarget.type().parameterCount() - 1 ; i++) {
                if (filterFromTarget.type().parameterType(i) != filterToTarget.type().parameterType(i)) {
                    throw newIllegalArgumentException("filterFromTarget and filterToTarget filter types do not match", filterFromTarget.type(), filterToTarget.type());
                } else {
                    newCoordinates.add(filterFromTarget.type().parameterType(i));
                    additionalCoordinates.add((filterFromTarget.type().parameterType(i)));
                }
            }
        }

        return new IndirectVarHandle(target, filterFromTarget.type().returnType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) -> {
                    int lastParameterPos = modeHandle.type().parameterCount() - 1;
                    return switch (mode.at) {
                        case GET -> MethodHandles.collectReturnValue(modeHandle, filterFromTarget);
                        case SET -> MethodHandles.collectArguments(modeHandle, lastParameterPos, filterToTarget);
                        case GET_AND_UPDATE -> {
                            MethodHandle adapter = MethodHandles.collectReturnValue(modeHandle, filterFromTarget);
                            MethodHandle res = MethodHandles.collectArguments(adapter, lastParameterPos, filterToTarget);
                            if (additionalCoordinates.size() > 0) {
                                res = joinDuplicateArgs(res, lastParameterPos,
                                        lastParameterPos + additionalCoordinates.size() + 1,
                                        additionalCoordinates.size());
                            }
                            yield res;
                        }
                        case COMPARE_AND_EXCHANGE -> {
                            MethodHandle adapter = MethodHandles.collectReturnValue(modeHandle, filterFromTarget);
                            adapter = MethodHandles.collectArguments(adapter, lastParameterPos, filterToTarget);
                            if (additionalCoordinates.size() > 0) {
                                adapter = joinDuplicateArgs(adapter, lastParameterPos,
                                        lastParameterPos + additionalCoordinates.size() + 1,
                                        additionalCoordinates.size());
                            }
                            MethodHandle res = MethodHandles.collectArguments(adapter, lastParameterPos - 1, filterToTarget);
                            if (additionalCoordinates.size() > 0) {
                                res = joinDuplicateArgs(res, lastParameterPos - 1,
                                        lastParameterPos + additionalCoordinates.size(),
                                        additionalCoordinates.size());
                            }
                            yield res;
                        }
                        case COMPARE_AND_SET -> {
                            MethodHandle adapter = MethodHandles.collectArguments(modeHandle, lastParameterPos, filterToTarget);
                            MethodHandle res = MethodHandles.collectArguments(adapter, lastParameterPos - 1, filterToTarget);
                            if (additionalCoordinates.size() > 0) {
                                res = joinDuplicateArgs(res, lastParameterPos - 1,
                                        lastParameterPos + additionalCoordinates.size(),
                                        additionalCoordinates.size());
                            }
                            yield res;
                        }
                    };
                });
    }

    private static MethodHandle joinDuplicateArgs(MethodHandle handle, int originalStart, int dropStart, int length) {
        int[] perms = new int[handle.type().parameterCount()];
        for (int i = 0 ; i < dropStart; i++) {
            perms[i] = i;
        }
        for (int i = 0 ; i < length ; i++) {
            perms[dropStart + i] = originalStart + i;
        }
        for (int i = dropStart + length ; i < perms.length ; i++) {
            perms[i] = i - length;
        }
        return MethodHandles.permuteArguments(handle,
                handle.type().dropParameterTypes(dropStart, dropStart + length),
                perms);
    }

    public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(filters);

        List<Class<?>> targetCoordinates = target.coordinateTypes();
        if (pos < 0 || pos >= targetCoordinates.size()) {
            throw newIllegalArgumentException("Invalid position " + pos + " for coordinate types", targetCoordinates);
        } else if (pos + filters.length > targetCoordinates.size()) {
            throw new IllegalArgumentException("Too many filters");
        }

        if (filters.length == 0) return target;

        List<Class<?>> newCoordinates = new ArrayList<>(targetCoordinates);
        for (int i = 0 ; i < filters.length ; i++) {
            MethodHandle filter = Objects.requireNonNull(filters[i]);
            filter = adaptForCheckedExceptions(filter);
            MethodType filterType = filter.type();
            if (filterType.parameterCount() != 1) {
                throw newIllegalArgumentException("Invalid filter type " + filterType);
            } else if (newCoordinates.get(pos + i) != filterType.returnType()) {
                throw newIllegalArgumentException("Invalid filter type " + filterType + " for coordinate type " + newCoordinates.get(i));
            }
            newCoordinates.set(pos + i, filters[i].type().parameterType(0));
        }

        return new IndirectVarHandle(target, target.varType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) -> MethodHandles.filterArguments(modeHandle, 1 + pos, filters));
    }

    public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(values);

        List<Class<?>> targetCoordinates = target.coordinateTypes();
        if (pos < 0 || pos >= targetCoordinates.size()) {
            throw newIllegalArgumentException("Invalid position " + pos + " for coordinate types", targetCoordinates);
        } else if (pos + values.length > targetCoordinates.size()) {
            throw new IllegalArgumentException("Too many values");
        }

        if (values.length == 0) return target;

        List<Class<?>> newCoordinates = new ArrayList<>(targetCoordinates);
        for (int i = 0 ; i < values.length ; i++) {
            Class<?> pt = newCoordinates.get(pos);
            if (pt.isPrimitive()) {
                Wrapper w = Wrapper.forPrimitiveType(pt);
                w.convert(values[i], pt);
            } else {
                pt.cast(values[i]);
            }
            newCoordinates.remove(pos);
        }

        return new IndirectVarHandle(target, target.varType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) -> MethodHandles.insertArguments(modeHandle, 1 + pos, values));
    }

    public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(newCoordinates);
        Objects.requireNonNull(reorder);

        List<Class<?>> targetCoordinates = target.coordinateTypes();
        MethodHandles.permuteArgumentChecks(reorder,
                MethodType.methodType(void.class, newCoordinates),
                MethodType.methodType(void.class, targetCoordinates));

        return new IndirectVarHandle(target, target.varType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) ->
                        MethodHandles.permuteArguments(modeHandle,
                                methodTypeFor(mode.at, modeHandle.type(), targetCoordinates, newCoordinates),
                                reorderArrayFor(mode.at, newCoordinates, reorder)));
    }

    private static int numTrailingArgs(VarHandle.AccessType at) {
        return switch (at) {
            case GET -> 0;
            case GET_AND_UPDATE, SET -> 1;
            case COMPARE_AND_SET, COMPARE_AND_EXCHANGE -> 2;
        };
    }

    private static int[] reorderArrayFor(VarHandle.AccessType at, List<Class<?>> newCoordinates, int[] reorder) {
        int numTrailingArgs = numTrailingArgs(at);
        int[] adjustedReorder = new int[reorder.length + 1 + numTrailingArgs];
        adjustedReorder[0] = 0;
        for (int i = 0 ; i < reorder.length ; i++) {
            adjustedReorder[i + 1] = reorder[i] + 1;
        }
        for (int i = 0 ; i < numTrailingArgs ; i++) {
            adjustedReorder[i + reorder.length + 1] = i + newCoordinates.size() + 1;
        }
        return adjustedReorder;
    }

    private static MethodType methodTypeFor(VarHandle.AccessType at, MethodType oldType, List<Class<?>> oldCoordinates, List<Class<?>> newCoordinates) {
        int numTrailingArgs = numTrailingArgs(at);
        MethodType adjustedType = MethodType.methodType(oldType.returnType(), oldType.parameterType(0));
        adjustedType = adjustedType.appendParameterTypes(newCoordinates);
        for (int i = 0 ; i < numTrailingArgs ; i++) {
            adjustedType = adjustedType.appendParameterTypes(oldType.parameterType(1 + oldCoordinates.size() + i));
        }
        return adjustedType;
    }

    public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle pFilter) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(pFilter);
        MethodHandle filter = adaptForCheckedExceptions(pFilter);

        List<Class<?>> targetCoordinates = target.coordinateTypes();
        if (pos < 0 || pos >= targetCoordinates.size()) {
            throw newIllegalArgumentException("Invalid position " + pos + " for coordinate types", targetCoordinates);
        } else if (filter.type().returnType() != void.class && filter.type().returnType() != targetCoordinates.get(pos)) {
            throw newIllegalArgumentException("Invalid filter type " + filter.type() + " for coordinate type " + targetCoordinates.get(pos));
        }

        List<Class<?>> newCoordinates = new ArrayList<>(targetCoordinates);
        if (filter.type().returnType() != void.class) {
            newCoordinates.remove(pos);
        }
        newCoordinates.addAll(pos, filter.type().parameterList());

        return new IndirectVarHandle(target, target.varType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) -> MethodHandles.collectArguments(modeHandle, 1 + pos, filter));
    }

    public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
        Objects.requireNonNull(target);
        Objects.requireNonNull(valueTypes);

        List<Class<?>> targetCoordinates = target.coordinateTypes();
        if (pos < 0 || pos > targetCoordinates.size()) {
            throw newIllegalArgumentException("Invalid position " + pos + " for coordinate types", targetCoordinates);
        }

        if (valueTypes.length == 0) return target;

        List<Class<?>> newCoordinates = new ArrayList<>(targetCoordinates);
        newCoordinates.addAll(pos, List.of(valueTypes));

        return new IndirectVarHandle(target, target.varType(), newCoordinates.toArray(new Class<?>[0]),
                (mode, modeHandle) -> MethodHandles.dropArguments(modeHandle, 1 + pos, valueTypes));
    }

    private static MethodHandle adaptForCheckedExceptions(MethodHandle target) {
        Class<?>[] exceptionTypes = exceptionTypes(target);
        if (exceptionTypes != null) { // exceptions known
            if (Stream.of(exceptionTypes).anyMatch(VarHandles::isCheckedException)) {
                throw newIllegalArgumentException("Cannot adapt a var handle with a method handle which throws checked exceptions");
            }
            return target; // no adaptation needed
        } else {
            MethodHandle handler = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_VarHandles_handleCheckedExceptions);
            MethodHandle zero = MethodHandles.zero(target.type().returnType()); // dead branch
            handler = MethodHandles.collectArguments(zero, 0, handler);
            return MethodHandles.catchException(target, Throwable.class, handler);
        }
    }

    static void handleCheckedExceptions(Throwable throwable) throws Throwable {
        if (isCheckedException(throwable.getClass())) {
            throw new IllegalStateException("Adapter handle threw checked exception", throwable);
        }
        throw throwable;
    }

    static Class<?>[] exceptionTypes(MethodHandle handle) {
        if (handle instanceof DirectMethodHandle directHandle) {
            byte refKind = directHandle.member.getReferenceKind();
            MethodHandleInfo info = new InfoFromMemberName(
                    MethodHandles.Lookup.IMPL_LOOKUP,
                    directHandle.member,
                    refKind);
            if (MethodHandleNatives.refKindIsMethod(refKind)) {
                return info.reflectAs(Method.class, MethodHandles.Lookup.IMPL_LOOKUP)
                        .getExceptionTypes();
            } else if (MethodHandleNatives.refKindIsField(refKind)) {
                return new Class<?>[0];
            } else if (MethodHandleNatives.refKindIsConstructor(refKind)) {
                return info.reflectAs(Constructor.class, MethodHandles.Lookup.IMPL_LOOKUP)
                        .getExceptionTypes();
            } else {
                throw new AssertionError("Cannot get here");
            }
        } else if (handle instanceof DelegatingMethodHandle delegatingMh) {
            return exceptionTypes(delegatingMh.getTarget());
        } else if (handle instanceof NativeMethodHandle) {
            return new Class<?>[0];
        }

        assert handle instanceof BoundMethodHandle : "Unexpected handle type: " + handle;
        // unknown
        return null;
    }

    private static boolean isCheckedException(Class<?> clazz) {
        return Throwable.class.isAssignableFrom(clazz) &&
                !RuntimeException.class.isAssignableFrom(clazz) &&
                !Error.class.isAssignableFrom(clazz);
    }

//    /**
//     * A helper program to generate the VarHandleGuards class with a set of
//     * static guard methods each of which corresponds to a particular shape and
//     * performs a type check of the symbolic type descriptor with the VarHandle
//     * type descriptor before linking/invoking to the underlying operation as
//     * characterized by the operation member name on the VarForm of the
//     * VarHandle.
//     * <p>
//     * The generated class essentially encapsulates pre-compiled LambdaForms,
//     * one for each method, for the most set of common method signatures.
//     * This reduces static initialization costs, footprint costs, and circular
//     * dependencies that may arise if a class is generated per LambdaForm.
//     * <p>
//     * A maximum of L*T*S methods will be generated where L is the number of
//     * access modes kinds (or unique operation signatures) and T is the number
//     * of variable types and S is the number of shapes (such as instance field,
//     * static field, or array access).
//     * If there are 4 unique operation signatures, 5 basic types (Object, int,
//     * long, float, double), and 3 shapes then a maximum of 60 methods will be
//     * generated.  However, the number is likely to be less since there
//     * be duplicate signatures.
//     * <p>
//     * Each method is annotated with @LambdaForm.Compiled to inform the runtime
//     * that such methods should be treated as if a method of a class that is the
//     * result of compiling a LambdaForm.  Annotation of such methods is
//     * important for correct evaluation of certain assertions and method return
//     * type profiling in HotSpot.
//     */
//    public static class GuardMethodGenerator {
//
//        static final String GUARD_METHOD_SIG_TEMPLATE = "<RETURN> <NAME>_<SIGNATURE>(<PARAMS>)";
//
//        static final String GUARD_METHOD_TEMPLATE =
//                """
//                @ForceInline
//                @LambdaForm.Compiled
//                @Hidden
//                static final <METHOD> throws Throwable {
//                    boolean direct = handle.checkAccessModeThenIsDirect(ad);
//                    if (direct && handle.vform.methodType_table[ad.type] == ad.symbolicMethodTypeErased) {
//                        <RESULT_ERASED>MethodHandle.linkToStatic(<LINK_TO_STATIC_ARGS>);<RETURN_ERASED>
//                    } else {
//                        MethodHandle mh = handle.getMethodHandle(ad.mode);
//                        <RETURN>mh.asType(ad.symbolicMethodTypeInvoker).invokeBasic(<LINK_TO_INVOKER_ARGS>);
//                    }
//                }""";
//
//        static final String GUARD_METHOD_TEMPLATE_V =
//                """
//                @ForceInline
//                @LambdaForm.Compiled
//                @Hidden
//                static final <METHOD> throws Throwable {
//                    boolean direct = handle.checkAccessModeThenIsDirect(ad);
//                    if (direct && handle.vform.methodType_table[ad.type] == ad.symbolicMethodTypeErased) {
//                        MethodHandle.linkToStatic(<LINK_TO_STATIC_ARGS>);
//                    } else if (direct && handle.vform.getMethodType_V(ad.type) == ad.symbolicMethodTypeErased) {
//                        MethodHandle.linkToStatic(<LINK_TO_STATIC_ARGS>);
//                    } else {
//                        MethodHandle mh = handle.getMethodHandle(ad.mode);
//                        mh.asType(ad.symbolicMethodTypeInvoker).invokeBasic(<LINK_TO_INVOKER_ARGS>);
//                    }
//                }""";
//
//        // A template for deriving the operations
//        // could be supported by annotating VarHandle directly with the
//        // operation kind and shape
//        interface VarHandleTemplate {
//            Object get();
//
//            void set(Object value);
//
//            boolean compareAndSet(Object actualValue, Object expectedValue);
//
//            Object compareAndExchange(Object actualValue, Object expectedValue);
//
//            Object getAndUpdate(Object value);
//        }
//
//        record HandleType(Class<?> receiver, Class<?>... intermediates) {
//        }
//
//        /**
//         * @param args parameters
//         */
//        public static void main(String[] args) {
//            System.out.println("package java.lang.invoke;");
//            System.out.println();
//            System.out.println("import jdk.internal.vm.annotation.ForceInline;");
//            System.out.println("import jdk.internal.vm.annotation.Hidden;");
//            System.out.println();
//            System.out.println("// This class is auto-generated by " +
//                               GuardMethodGenerator.class.getName() +
//                               ". Do not edit.");
//            System.out.println("final class VarHandleGuards {");
//
//            System.out.println();
//
//            // Declare the stream of shapes
//            List<HandleType> hts = List.of(
//                    // Object->T
//                    new HandleType(Object.class),
//
//                    // <static>->T
//                    new HandleType(null),
//
//                    // Array[index]->T
//                    new HandleType(Object.class, int.class),
//
//                    // MS[base]->T
//                    new HandleType(Object.class, long.class),
//
//                    // MS[base][offset]->T
//                    new HandleType(Object.class, long.class, long.class)
//            );
//
//            Stream.of(VarHandleTemplate.class.getMethods()).<MethodType>
//                    mapMulti((m, sink) -> {
//                        for (var ht : hts) {
//                            for (var bt : LambdaForm.BasicType.ARG_TYPES) {
//                                sink.accept(generateMethodType(m, ht.receiver, bt.btClass, ht.intermediates));
//                            }
//                        }
//                    }).
//                    distinct().
//                    map(GuardMethodGenerator::generateMethod).
//                    forEach(System.out::println);
//
//            System.out.println("}");
//        }
//
//        static MethodType generateMethodType(Method m, Class<?> receiver, Class<?> value, Class<?>... intermediates) {
//            Class<?> returnType = m.getReturnType() == Object.class
//                                  ? value : m.getReturnType();
//
//            List<Class<?>> params = new ArrayList<>();
//            if (receiver != null)
//                params.add(receiver);
//            java.util.Collections.addAll(params, intermediates);
//            for (var p : m.getParameters()) {
//                params.add(value);
//            }
//            return MethodType.methodType(returnType, params);
//        }
//
//        static String generateMethod(MethodType mt) {
//            Class<?> returnType = mt.returnType();
//
//            var params = new java.util.LinkedHashMap<String, Class<?>>();
//            params.put("handle", VarHandle.class);
//            for (int i = 0; i < mt.parameterCount(); i++) {
//                params.put("arg" + i, mt.parameterType(i));
//            }
//            params.put("ad", VarHandle.AccessDescriptor.class);
//
//            // Generate method signature line
//            String RETURN = className(returnType);
//            String NAME = "guard";
//            String SIGNATURE = getSignature(mt);
//            String PARAMS = params.entrySet().stream().
//                    map(e -> className(e.getValue()) + " " + e.getKey()).
//                    collect(java.util.stream.Collectors.joining(", "));
//            String METHOD = GUARD_METHOD_SIG_TEMPLATE.
//                    replace("<RETURN>", RETURN).
//                    replace("<NAME>", NAME).
//                    replace("<SIGNATURE>", SIGNATURE).
//                    replace("<PARAMS>", PARAMS);
//
//            // Generate method
//            params.remove("ad");
//
//            List<String> LINK_TO_STATIC_ARGS = new ArrayList<>(params.keySet());
//            LINK_TO_STATIC_ARGS.add("handle.vform.getMemberName(ad.mode)");
//
//            List<String> LINK_TO_INVOKER_ARGS = new ArrayList<>(params.keySet());
//            LINK_TO_INVOKER_ARGS.set(0, LINK_TO_INVOKER_ARGS.get(0) + ".asDirect()");
//
//            RETURN = returnType == void.class
//                     ? ""
//                     : returnType == Object.class
//                       ? "return "
//                       : "return (" + returnType.getName() + ") ";
//
//            String RESULT_ERASED = returnType == void.class
//                                   ? ""
//                                   : returnType != Object.class
//                                     ? "return (" + returnType.getName() + ") "
//                                     : "Object r = ";
//
//            String RETURN_ERASED = returnType != Object.class
//                                   ? ""
//                                   : "\n        return ad.returnType.cast(r);";
//
//            String template = returnType == void.class
//                              ? GUARD_METHOD_TEMPLATE_V
//                              : GUARD_METHOD_TEMPLATE;
//            return template.
//                    replace("<METHOD>", METHOD).
//                    replace("<NAME>", NAME).
//                    replaceAll("<RETURN>", RETURN).
//                    replace("<RESULT_ERASED>", RESULT_ERASED).
//                    replace("<RETURN_ERASED>", RETURN_ERASED).
//                    replaceAll("<LINK_TO_STATIC_ARGS>", String.join(", ", LINK_TO_STATIC_ARGS)).
//                    replace("<LINK_TO_INVOKER_ARGS>", String.join(", ", LINK_TO_INVOKER_ARGS))
//                    .indent(4);
//        }
//
//        static String className(Class<?> c) {
//            String n = c.getName();
//            if (n.startsWith("java.lang.")) {
//                n = n.replace("java.lang.", "");
//                if (n.startsWith("invoke.")) {
//                    n = n.replace("invoke.", "");
//                }
//            }
//            return n.replace('$', '.');
//        }
//
//        static String getSignature(MethodType m) {
//            StringBuilder sb = new StringBuilder(m.parameterCount() + 1);
//
//            for (int i = 0; i < m.parameterCount(); i++) {
//                Class<?> pt = m.parameterType(i);
//                sb.append(getCharType(pt));
//            }
//
//            sb.append('_').append(getCharType(m.returnType()));
//
//            return sb.toString();
//        }
//
//        static char getCharType(Class<?> pt) {
//            return Wrapper.forBasicType(pt).basicTypeChar();
//        }
//    }
}