java Unsafe api with docs, DO NOT use this in production

MyUnsafeFactory.java

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.Map;
import java.util.Objects;

@SuppressWarnings({"WeakerAccess", "unused"})
public class MyUnsafeFactory {

    /**
     * Provides the caller with the capability of performing unsafe
     * operations.
     *
     * <p>The returned {@code Unsafe} object should be carefully guarded
     * by the caller, since it can be used to read and write data at arbitrary
     * memory addresses.  It must never be passed to untrusted code.
     *
     * <p>Most methods in this class are very low-level, and correspond to a
     * small number of hardware instructions (on typical machines).  Compilers
     * are encouraged to optimize these methods accordingly.
     *
     * <p>Here is a suggested idiom for using unsafe operations:
     *
     * <pre> {@code
     * class MyTrustedClass {
     *   private static final Unsafe unsafe = Unsafe.getUnsafe();
     *   ...
     *   private long myCountAddress = ...;
     *   public int getCount() { return unsafe.getByte(myCountAddress); }
     * }}</pre>
     * <p>
     * (It may assist compilers to make the local variable {@code final}.)
     */
    public static IUnsafe getUnsafe() {
        return (IUnsafe) Proxy.newProxyInstance(IUnsafe.class.getClassLoader(),
                new Class<?>[]{IUnsafe.class},
                ((proxy, method, args) -> findMethod(method).invoke(theUnsafe, args)));
    }

    /**
     * Get the RAW instance of unsafe
     *
     * @return unsafe
     */
    public static Object getTheUnsafe() {
        return theUnsafe;
    }

    /**
     * Check if method is available
     *
     * @param name     method name
     * @param argTypes method argument types
     * @return available or not
     */
    public static boolean hasMethod(final String name, final Class<?>... argTypes) {
        return map.containsKey(new MethodDef(name, argTypes));
    }

    @SuppressWarnings({"unused", "WeakerAccess"})
    public static class UnsafeException extends RuntimeException {
        public UnsafeException(String message) {
            super(message);
        }

        public UnsafeException(String message, Throwable cause) {
            super(message, cause);
        }

        public UnsafeException(Throwable cause) {
            super(cause);
        }

        private static final long serialVersionUID = -1201190518070455522L;
    }

    private static final class MethodDef {
        final String methodName;
        final Class<?>[] argTypes;

        private MethodDef(String methodName, Class<?>[] argTypes) {
            this.methodName = methodName;
            this.argTypes = argTypes;
        }

        private MethodDef(final Method method) {
            this.methodName = Objects.requireNonNull(method.getName());
            this.argTypes = Objects.requireNonNull(method.getParameterTypes());
        }

        private static MethodDef of(final Method method) {
            return new MethodDef(method);
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof MethodDef)) return false;
            MethodDef methodDef = (MethodDef) o;
            return methodName.equals(methodDef.methodName) &&
                    Arrays.equals(argTypes, methodDef.argTypes);
        }

        @Override
        public int hashCode() {
            return 31 * Objects.hash(methodName) + Arrays.hashCode(argTypes);
        }
    }

    private static final Class<?> unsafeClass;
    private static final Object theUnsafe;
    private static final Map<MethodDef, Method> map;

    private static Method findMethod(final Method method) {
        final var def = MethodDef.of(method);
        final var theMethod = map.get(def);
        if (theMethod == null) {
            throw new UnsafeException("Method " + method.getName() + " not found");
        }
        return theMethod;
    }

    private static int readInt(String fieldName)
            throws IllegalAccessException, NoSuchFieldException {
        final var field = unsafeClass.getDeclaredField(fieldName);
        return field.getInt(null);
    }

    /**
     * This constant differs from all results that will ever be returned from
     * {@link IUnsafe#staticFieldOffset}, {@link IUnsafe#objectFieldOffset},
     * or {@link IUnsafe#arrayBaseOffset}.
     */
    public static final int INVALID_FIELD_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(boolean[].class)}
     */
    public static final int ARRAY_BOOLEAN_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(byte[].class)}
     */
    public static final int ARRAY_BYTE_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(short[].class)}
     */
    public static final int ARRAY_SHORT_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(char[].class)}
     */
    public static final int ARRAY_CHAR_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(int[].class)}
     */
    public static final int ARRAY_INT_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(long[].class)}
     */
    public static final int ARRAY_LONG_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(float[].class)}
     */
    public static final int ARRAY_FLOAT_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(double[].class)}
     */
    public static final int ARRAY_DOUBLE_BASE_OFFSET;

    /**
     * The value of {@code arrayBaseOffset(Object[].class)}
     */
    public static final int ARRAY_OBJECT_BASE_OFFSET;

    /**
     * The value of {@code arrayIndexScale(boolean[].class)}
     */
    public static final int ARRAY_BOOLEAN_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(byte[].class)}
     */
    public static final int ARRAY_BYTE_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(short[].class)}
     */
    public static final int ARRAY_SHORT_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(char[].class)}
     */
    public static final int ARRAY_CHAR_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(int[].class)}
     */
    public static final int ARRAY_INT_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(long[].class)}
     */
    public static final int ARRAY_LONG_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(float[].class)}
     */
    public static final int ARRAY_FLOAT_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(double[].class)}
     */
    public static final int ARRAY_DOUBLE_INDEX_SCALE;

    /**
     * The value of {@code arrayIndexScale(Object[].class)}
     */
    public static final int ARRAY_OBJECT_INDEX_SCALE;

    /**
     * The value of {@code addressSize()}
     */
    public static final int ADDRESS_SIZE;

    static {
        try {
            unsafeClass = Class.forName("sun.misc.Unsafe");
            final var theUnsafeField = unsafeClass.getDeclaredField("theUnsafe");
            theUnsafeField.setAccessible(true);
            theUnsafe = theUnsafeField.get(null);

            final Method[] methods = unsafeClass.getMethods();
            @SuppressWarnings("unchecked") final Map.Entry<MethodDef, Method>[] entries = new Map.Entry[methods.length];
            for (int i = 0; i < methods.length; i++) {
                final Method method = methods[i];
                entries[i] = Map.entry(MethodDef.of(method), method);
            }
            map = Map.ofEntries(entries);
            ADDRESS_SIZE = readInt("ADDRESS_SIZE");
            INVALID_FIELD_OFFSET = readInt("INVALID_FIELD_OFFSET");
            ARRAY_BOOLEAN_BASE_OFFSET = readInt("ARRAY_BOOLEAN_BASE_OFFSET");
            ARRAY_BYTE_BASE_OFFSET = readInt("ARRAY_BYTE_BASE_OFFSET");
            ARRAY_SHORT_BASE_OFFSET = readInt("ARRAY_SHORT_BASE_OFFSET");
            ARRAY_CHAR_BASE_OFFSET = readInt("ARRAY_CHAR_BASE_OFFSET");
            ARRAY_INT_BASE_OFFSET = readInt("ARRAY_INT_BASE_OFFSET");
            ARRAY_LONG_BASE_OFFSET = readInt("ARRAY_LONG_BASE_OFFSET");
            ARRAY_FLOAT_BASE_OFFSET = readInt("ARRAY_FLOAT_BASE_OFFSET");
            ARRAY_DOUBLE_BASE_OFFSET = readInt("ARRAY_DOUBLE_BASE_OFFSET");
            ARRAY_OBJECT_BASE_OFFSET = readInt("ARRAY_OBJECT_BASE_OFFSET");
            ARRAY_BOOLEAN_INDEX_SCALE = readInt("ARRAY_BOOLEAN_INDEX_SCALE");
            ARRAY_BYTE_INDEX_SCALE = readInt("ARRAY_BYTE_INDEX_SCALE");
            ARRAY_SHORT_INDEX_SCALE = readInt("ARRAY_SHORT_INDEX_SCALE");
            ARRAY_CHAR_INDEX_SCALE = readInt("ARRAY_CHAR_INDEX_SCALE");
            ARRAY_INT_INDEX_SCALE = readInt("ARRAY_INT_INDEX_SCALE");
            ARRAY_LONG_INDEX_SCALE = readInt("ARRAY_LONG_INDEX_SCALE");
            ARRAY_FLOAT_INDEX_SCALE = readInt("ARRAY_FLOAT_INDEX_SCALE");
            ARRAY_DOUBLE_INDEX_SCALE = readInt("ARRAY_DOUBLE_INDEX_SCALE");
            ARRAY_OBJECT_INDEX_SCALE = readInt("ARRAY_OBJECT_INDEX_SCALE");
        } catch (ClassNotFoundException e) {
            throw new UnsafeException("Unsafe class not found", e);
        } catch (NoSuchFieldException e) {
            throw new UnsafeException(e);
        } catch (IllegalAccessException e) {
            throw new UnsafeException("Can not get unsafe instance", e);
        }
    }

    @SuppressWarnings("unused")
    public interface IUnsafe {

        /**
         * Provides the caller with the capability of performing unsafe
         * operations.
         *
         * <p>The returned {@code Unsafe} object should be carefully guarded
         * by the caller, since it can be used to read and write data at arbitrary
         * memory addresses.  It must never be passed to untrusted code.
         *
         * <p>Most methods in this class are very low-level, and correspond to a
         * small number of hardware instructions (on typical machines).  Compilers
         * are encouraged to optimize these methods accordingly.
         *
         * <p>Here is a suggested idiom for using unsafe operations:
         *
         * <pre> {@code
         * class MyTrustedClass {
         *   private static final Unsafe unsafe = Unsafe.getUnsafe();
         *   ...
         *   private long myCountAddress = ...;
         *   public int getCount() { return unsafe.getByte(myCountAddress); }
         * }}</pre>
         * <p>
         * (It may assist compilers to make the local variable {@code final}.)
         *
         * @throws SecurityException if the class loader of the caller
         *                           class is not in the system domain in which all permissions
         *                           are granted.
         */

        static IUnsafe getUnsafe() {
            return MyUnsafeFactory.getUnsafe();
        }

        /// peek and poke operations
        /// (compilers should optimize these to memory ops)

        // These work on object fields in the Java heap.
        // They will not work on elements of packed arrays.

        /**
         * Fetches a value from a given Java variable.
         * More specifically, fetches a field or array element within the given
         * object {@code o} at the given offset, or (if {@code o} is null)
         * from the memory address whose numerical value is the given offset.
         * <p>
         * The results are undefined unless one of the following cases is true:
         * <ul>
         * <li>The offset was obtained from {@link #objectFieldOffset} on
         * the {@link java.lang.reflect.Field} of some Java field and the object
         * referred to by {@code o} is of a class compatible with that
         * field's class.
         *
         * <li>The offset and object reference {@code o} (either null or
         * non-null) were both obtained via {@link #staticFieldOffset}
         * and {@link #staticFieldBase} (respectively) from the
         * reflective {@link Field} representation of some Java field.
         *
         * <li>The object referred to by {@code o} is an array, and the offset
         * is an integer of the form {@code B+N*S}, where {@code N} is
         * a valid index into the array, and {@code B} and {@code S} are
         * the values obtained by {@link #arrayBaseOffset} and {@link
         * #arrayIndexScale} (respectively) from the array's class.  The value
         * referred to is the {@code N}<em>th</em> element of the array.
         *
         * </ul>
         * <p>
         * If one of the above cases is true, the call references a specific Java
         * variable (field or array element).  However, the results are undefined
         * if that variable is not in fact of the type returned by this method.
         * <p>
         * This method refers to a variable by means of two parameters, and so
         * it provides (in effect) a <em>double-register</em> addressing mode
         * for Java variables.  When the object reference is null, this method
         * uses its offset as an absolute address.  This is similar in operation
         * to methods such as {@link #getInt(long)}, which provide (in effect) a
         * <em>single-register</em> addressing mode for non-Java variables.
         * However, because Java variables may have a different layout in memory
         * from non-Java variables, programmers should not assume that these
         * two addressing modes are ever equivalent.  Also, programmers should
         * remember that offsets from the double-register addressing mode cannot
         * be portably confused with longs used in the single-register addressing
         * mode.
         *
         * @param o      Java heap object in which the variable resides, if any, else
         *               null
         * @param offset indication of where the variable resides in a Java heap
         *               object, if any, else a memory address locating the variable
         *               statically
         * @return the value fetched from the indicated Java variable
         * @throws RuntimeException No defined exceptions are thrown, not even
         *                          {@link NullPointerException}
         */

        int getInt(Object o, long offset);

        /**
         * Stores a value into a given Java variable.
         * <p>
         * The first two parameters are interpreted exactly as with
         * {@link #getInt(Object, long)} to refer to a specific
         * Java variable (field or array element).  The given value
         * is stored into that variable.
         * <p>
         * The variable must be of the same type as the method
         * parameter {@code x}.
         *
         * @param o      Java heap object in which the variable resides, if any, else
         *               null
         * @param offset indication of where the variable resides in a Java heap
         *               object, if any, else a memory address locating the variable
         *               statically
         * @param x      the value to store into the indicated Java variable
         * @throws RuntimeException No defined exceptions are thrown, not even
         *                          {@link NullPointerException}
         */

        void putInt(Object o, long offset, int x);

        /**
         * Fetches a reference value from a given Java variable.
         *
         * @see #getInt(Object, long)
         */

        Object getObject(Object o, long offset);

        /**
         * Stores a reference value into a given Java variable.
         * <p>
         * Unless the reference {@code x} being stored is either null
         * or matches the field type, the results are undefined.
         * If the reference {@code o} is non-null, card marks or
         * other store barriers for that object (if the VM requires them)
         * are updated.
         *
         * @see #putInt(Object, long, int)
         */

        void putObject(Object o, long offset, Object x);

        /**
         * @see #getInt(Object, long)
         */

        boolean getBoolean(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putBoolean(Object o, long offset, boolean x);

        /**
         * @see #getInt(Object, long)
         */

        byte getByte(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putByte(Object o, long offset, byte x);

        /**
         * @see #getInt(Object, long)
         */

        short getShort(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putShort(Object o, long offset, short x);

        /**
         * @see #getInt(Object, long)
         */

        char getChar(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putChar(Object o, long offset, char x);

        /**
         * @see #getInt(Object, long)
         */

        long getLong(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putLong(Object o, long offset, long x);

        /**
         * @see #getInt(Object, long)
         */

        float getFloat(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putFloat(Object o, long offset, float x);

        /**
         * @see #getInt(Object, long)
         */

        double getDouble(Object o, long offset);

        /**
         * @see #putInt(Object, long, int)
         */

        void putDouble(Object o, long offset, double x);

        // These work on values in the C heap.

        /**
         * Fetches a value from a given memory address.  If the address is zero, or
         * does not point into a block obtained from {@link #allocateMemory}, the
         * results are undefined.
         *
         * @see #allocateMemory
         */

        byte getByte(long address);

        /**
         * Stores a value into a given memory address.  If the address is zero, or
         * does not point into a block obtained from {@link #allocateMemory}, the
         * results are undefined.
         *
         * @see #getByte(long)
         */

        void putByte(long address, byte x);

        /**
         * @see #getByte(long)
         */

        short getShort(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putShort(long address, short x);

        /**
         * @see #getByte(long)
         */

        char getChar(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putChar(long address, char x);

        /**
         * @see #getByte(long)
         */

        int getInt(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putInt(long address, int x);

        /**
         * @see #getByte(long)
         */

        long getLong(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putLong(long address, long x);

        /**
         * @see #getByte(long)
         */

        float getFloat(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putFloat(long address, float x);

        /**
         * @see #getByte(long)
         */

        double getDouble(long address);

        /**
         * @see #putByte(long, byte)
         */

        void putDouble(long address, double x);


        /**
         * Fetches a native pointer from a given memory address.  If the address is
         * zero, or does not point into a block obtained from {@link
         * #allocateMemory}, the results are undefined.
         *
         * <p>If the native pointer is less than 64 bits wide, it is extended as
         * an unsigned number to a Java long.  The pointer may be indexed by any
         * given byte offset, simply by adding that offset (as a simple integer) to
         * the long representing the pointer.  The number of bytes actually read
         * from the target address may be determined by consulting {@link
         * #addressSize}.
         *
         * @see #allocateMemory
         */

        long getAddress(long address);

        /**
         * Stores a native pointer into a given memory address.  If the address is
         * zero, or does not point into a block obtained from {@link
         * #allocateMemory}, the results are undefined.
         *
         * <p>The number of bytes actually written at the target address may be
         * determined by consulting {@link #addressSize}.
         *
         * @see #getAddress(long)
         */

        void putAddress(long address, long x);


        /// wrappers for malloc, realloc, free:

        /**
         * Allocates a new block of native memory, of the given size in bytes.  The
         * contents of the memory are uninitialized; they will generally be
         * garbage.  The resulting native pointer will never be zero, and will be
         * aligned for all value types.  Dispose of this memory by calling {@link
         * #freeMemory}, or resize it with {@link #reallocateMemory}.
         *
         * <em>Note:</em> It is the resposibility of the caller to make
         * sure arguments are checked before the methods are called. While
         * some rudimentary checks are performed on the input, the checks
         * are best effort and when performance is an overriding priority,
         * as when methods of this class are optimized by the runtime
         * compiler, some or all checks (if any) may be elided. Hence, the
         * caller must not rely on the checks and corresponding
         * exceptions!
         *
         * @throws RuntimeException if the size is negative or too large
         *                          for the native size_t type
         * @throws OutOfMemoryError if the allocation is refused by the system
         * @see #getByte(long)
         * @see #putByte(long, byte)
         */

        long allocateMemory(long bytes);

        /**
         * Resizes a new block of native memory, to the given size in bytes.  The
         * contents of the new block past the size of the old block are
         * uninitialized; they will generally be garbage.  The resulting native
         * pointer will be zero if and only if the requested size is zero.  The
         * resulting native pointer will be aligned for all value types.  Dispose
         * of this memory by calling {@link #freeMemory}, or resize it with {@link
         * #reallocateMemory}.  The address passed to this method may be null, in
         * which case an allocation will be performed.
         *
         * <em>Note:</em> It is the resposibility of the caller to make
         * sure arguments are checked before the methods are called. While
         * some rudimentary checks are performed on the input, the checks
         * are best effort and when performance is an overriding priority,
         * as when methods of this class are optimized by the runtime
         * compiler, some or all checks (if any) may be elided. Hence, the
         * caller must not rely on the checks and corresponding
         * exceptions!
         *
         * @throws RuntimeException if the size is negative or too large
         *                          for the native size_t type
         * @throws OutOfMemoryError if the allocation is refused by the system
         * @see #allocateMemory
         */

        @SuppressWarnings("JavaDoc")
        long reallocateMemory(long address, long bytes);

        /**
         * Sets all bytes in a given block of memory to a fixed value
         * (usually zero).
         *
         * <p>This method determines a block's base address by means of two parameters,
         * and so it provides (in effect) a <em>double-register</em> addressing mode,
         * as discussed in {@link #getInt(Object, long)}.  When the object reference is null,
         * the offset supplies an absolute base address.
         *
         * <p>The stores are in coherent (atomic) units of a size determined
         * by the address and length parameters.  If the effective address and
         * length are all even modulo 8, the stores take place in 'long' units.
         * If the effective address and length are (resp.) even modulo 4 or 2,
         * the stores take place in units of 'int' or 'short'.
         *
         * <em>Note:</em> It is the resposibility of the caller to make
         * sure arguments are checked before the methods are called. While
         * some rudimentary checks are performed on the input, the checks
         * are best effort and when performance is an overriding priority,
         * as when methods of this class are optimized by the runtime
         * compiler, some or all checks (if any) may be elided. Hence, the
         * caller must not rely on the checks and corresponding
         * exceptions!
         *
         * @throws RuntimeException if any of the arguments is invalid
         * @since 1.7
         */

        void setMemory(Object o, long offset, long bytes, byte value);

        /**
         * Sets all bytes in a given block of memory to a fixed value
         * (usually zero).  This provides a <em>single-register</em> addressing mode,
         * as discussed in {@link #getInt(Object, long)}.
         *
         * <p>Equivalent to {@code setMemory(null, address, bytes, value)}.
         */

        void setMemory(long address, long bytes, byte value);

        /**
         * Sets all bytes in a given block of memory to a copy of another
         * block.
         *
         * <p>This method determines each block's base address by means of two parameters,
         * and so it provides (in effect) a <em>double-register</em> addressing mode,
         * as discussed in {@link #getInt(Object, long)}.  When the object reference is null,
         * the offset supplies an absolute base address.
         *
         * <p>The transfers are in coherent (atomic) units of a size determined
         * by the address and length parameters.  If the effective addresses and
         * length are all even modulo 8, the transfer takes place in 'long' units.
         * If the effective addresses and length are (resp.) even modulo 4 or 2,
         * the transfer takes place in units of 'int' or 'short'.
         *
         * <em>Note:</em> It is the resposibility of the caller to make
         * sure arguments are checked before the methods are called. While
         * some rudimentary checks are performed on the input, the checks
         * are best effort and when performance is an overriding priority,
         * as when methods of this class are optimized by the runtime
         * compiler, some or all checks (if any) may be elided. Hence, the
         * caller must not rely on the checks and corresponding
         * exceptions!
         *
         * @throws RuntimeException if any of the arguments is invalid
         * @since 1.7
         */

        void copyMemory(Object srcBase, long srcOffset,
                        Object destBase, long destOffset,
                        long bytes);

        /**
         * Sets all bytes in a given block of memory to a copy of another
         * block.  This provides a <em>single-register</em> addressing mode,
         * as discussed in {@link #getInt(Object, long)}.
         * <p>
         * Equivalent to {@code copyMemory(null, srcAddress, null, destAddress, bytes)}.
         */

        void copyMemory(long srcAddress, long destAddress, long bytes);

        /**
         * Disposes of a block of native memory, as obtained from {@link
         * #allocateMemory} or {@link #reallocateMemory}.  The address passed to
         * this method may be null, in which case no action is taken.
         *
         * <em>Note:</em> It is the resposibility of the caller to make
         * sure arguments are checked before the methods are called. While
         * some rudimentary checks are performed on the input, the checks
         * are best effort and when performance is an overriding priority,
         * as when methods of this class are optimized by the runtime
         * compiler, some or all checks (if any) may be elided. Hence, the
         * caller must not rely on the checks and corresponding
         * exceptions!
         *
         * @throws RuntimeException if any of the arguments is invalid
         * @see #allocateMemory
         */

        void freeMemory(long address);

        /// random queries


        /**
         * Reports the location of a given field in the storage allocation of its
         * class.  Do not expect to perform any sort of arithmetic on this offset;
         * it is just a cookie which is passed to the unsafe heap memory accessors.
         *
         * <p>Any given field will always have the same offset and base, and no
         * two distinct fields of the same class will ever have the same offset
         * and base.
         *
         * <p>As of 1.4.1, offsets for fields are represented as long values,
         * although the Sun JVM does not use the most significant 32 bits.
         * However, JVM implementations which store static fields at absolute
         * addresses can use long offsets and null base pointers to express
         * the field locations in a form usable by {@link #getInt(Object, long)}.
         * Therefore, code which will be ported to such JVMs on 64-bit platforms
         * must preserve all bits of static field offsets.
         *
         * @see #getInt(Object, long)
         */

        long objectFieldOffset(Field f);

        /**
         * Reports the location of a given static field, in conjunction with {@link
         * #staticFieldBase}.
         * <p>Do not expect to perform any sort of arithmetic on this offset;
         * it is just a cookie which is passed to the unsafe heap memory accessors.
         *
         * <p>Any given field will always have the same offset, and no two distinct
         * fields of the same class will ever have the same offset.
         *
         * <p>As of 1.4.1, offsets for fields are represented as long values,
         * although the Sun JVM does not use the most significant 32 bits.
         * It is hard to imagine a JVM technology which needs more than
         * a few bits to encode an offset within a non-array object,
         * However, for consistency with other methods in this class,
         * this method reports its result as a long value.
         *
         * @see #getInt(Object, long)
         */

        long staticFieldOffset(Field f);

        /**
         * Reports the location of a given static field, in conjunction with {@link
         * #staticFieldOffset}.
         * <p>Fetch the base "Object", if any, with which static fields of the
         * given class can be accessed via methods like {@link #getInt(Object,
         * long)}.  This value may be null.  This value may refer to an object
         * which is a "cookie", not guaranteed to be a real Object, and it should
         * not be used in any way except as argument to the get and put routines in
         * this class.
         */

        Object staticFieldBase(Field f);

        /**
         * Detects if the given class may need to be initialized. This is often
         * needed in conjunction with obtaining the static field base of a
         * class.
         *
         * @return false only if a call to {@code ensureClassInitialized} would have no effect
         */

        boolean shouldBeInitialized(Class<?> c);

        /**
         * Ensures the given class has been initialized. This is often
         * needed in conjunction with obtaining the static field base of a
         * class.
         */

        void ensureClassInitialized(Class<?> c);

        /**
         * Reports the offset of the first element in the storage allocation of a
         * given array class.  If {@link #arrayIndexScale} returns a non-zero value
         * for the same class, you may use that scale factor, together with this
         * base offset, to form new offsets to access elements of arrays of the
         * given class.
         *
         * @see #getInt(Object, long)
         * @see #putInt(Object, long, int)
         */

        int arrayBaseOffset(Class<?> arrayClass);

        /**
         * Reports the scale factor for addressing elements in the storage
         * allocation of a given array class.  However, arrays of "narrow" types
         * will generally not work properly with accessors like {@link
         * #getByte(Object, long)}, so the scale factor for such classes is reported
         * as zero.
         *
         * @see #arrayBaseOffset
         * @see #getInt(Object, long)
         * @see #putInt(Object, long, int)
         */

        int arrayIndexScale(Class<?> arrayClass);

        /**
         * Reports the size in bytes of a native pointer, as stored via {@link
         * #putAddress}.  This value will be either 4 or 8.  Note that the sizes of
         * other primitive types (as stored in native memory blocks) is determined
         * fully by their information content.
         */

        int addressSize();


        /**
         * Reports the size in bytes of a native memory page (whatever that is).
         * This value will always be a power of two.
         */

        int pageSize();


        /// random trusted operations from JNI:

        /**
         * Defines a class but does not make it known to the class loader or system dictionary.
         * <p>
         * For each CP entry, the corresponding CP patch must either be null or have
         * the a format that matches its tag:
         * <ul>
         * <li>Integer, Long, Float, Double: the corresponding wrapper object type from java.lang
         * <li>Utf8: a string (must have suitable syntax if used as signature or name)
         * <li>Class: any java.lang.Class object
         * <li>String: any object (not just a java.lang.String)
         * <li>InterfaceMethodRef: (NYI) a method handle to invoke on that call site's arguments
         * </ul>
         *
         * @param hostClass context for linkage, access control, protection domain, and class loader
         * @param data      bytes of a class file
         * @param cpPatches where non-null entries exist, they replace corresponding CP entries in data
         */

        Class<?> defineAnonymousClass(Class<?> hostClass, byte[] data, Object[] cpPatches);

        /**
         * Allocates an instance but does not run any constructor.
         * Initializes the class if it has not yet been.
         */

        Object allocateInstance(Class<?> cls)
                throws InstantiationException;

        /**
         * Throws the exception without telling the verifier.
         */

        void throwException(Throwable ee);

        /**
         * Atomically updates Java variable to {@code x} if it is currently
         * holding {@code expected}.
         *
         * <p>This operation has memory semantics of a {@code volatile} read
         * and write.  Corresponds to C11 atomic_compare_exchange_strong.
         *
         * @return {@code true} if successful
         */

        boolean compareAndSwapObject(Object o, long offset,
                                     Object expected,
                                     Object x);

        /**
         * Atomically updates Java variable to {@code x} if it is currently
         * holding {@code expected}.
         *
         * <p>This operation has memory semantics of a {@code volatile} read
         * and write.  Corresponds to C11 atomic_compare_exchange_strong.
         *
         * @return {@code true} if successful
         */

        boolean compareAndSwapInt(Object o, long offset,
                                  int expected,
                                  int x);

        /**
         * Atomically updates Java variable to {@code x} if it is currently
         * holding {@code expected}.
         *
         * <p>This operation has memory semantics of a {@code volatile} read
         * and write.  Corresponds to C11 atomic_compare_exchange_strong.
         *
         * @return {@code true} if successful
         */

        boolean compareAndSwapLong(Object o, long offset,
                                   long expected,
                                   long x);

        /**
         * Fetches a reference value from a given Java variable, with volatile
         * load semantics. Otherwise identical to {@link #getObject(Object, long)}
         */

        Object getObjectVolatile(Object o, long offset);

        /**
         * Stores a reference value into a given Java variable, with
         * volatile store semantics. Otherwise identical to {@link #putObject(Object, long, Object)}
         */

        void putObjectVolatile(Object o, long offset, Object x);

        /**
         * Volatile version of {@link #getInt(Object, long)}
         */

        int getIntVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putInt(Object, long, int)}
         */

        void putIntVolatile(Object o, long offset, int x);

        /**
         * Volatile version of {@link #getBoolean(Object, long)}
         */

        boolean getBooleanVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putBoolean(Object, long, boolean)}
         */

        void putBooleanVolatile(Object o, long offset, boolean x);

        /**
         * Volatile version of {@link #getByte(Object, long)}
         */

        byte getByteVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putByte(Object, long, byte)}
         */

        void putByteVolatile(Object o, long offset, byte x);

        /**
         * Volatile version of {@link #getShort(Object, long)}
         */

        short getShortVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putShort(Object, long, short)}
         */

        void putShortVolatile(Object o, long offset, short x);

        /**
         * Volatile version of {@link #getChar(Object, long)}
         */

        char getCharVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putChar(Object, long, char)}
         */

        void putCharVolatile(Object o, long offset, char x);

        /**
         * Volatile version of {@link #getLong(Object, long)}
         */

        long getLongVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putLong(Object, long, long)}
         */

        void putLongVolatile(Object o, long offset, long x);

        /**
         * Volatile version of {@link #getFloat(Object, long)}
         */

        float getFloatVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putFloat(Object, long, float)}
         */

        void putFloatVolatile(Object o, long offset, float x);

        /**
         * Volatile version of {@link #getDouble(Object, long)}
         */

        double getDoubleVolatile(Object o, long offset);

        /**
         * Volatile version of {@link #putDouble(Object, long, double)}
         */

        void putDoubleVolatile(Object o, long offset, double x);

        /**
         * Version of {@link #putObjectVolatile(Object, long, Object)}
         * that does not guarantee immediate visibility of the store to
         * other threads. This method is generally only useful if the
         * underlying field is a Java volatile (or if an array cell, one
         * that is otherwise only accessed using volatile accesses).
         * <p>
         * Corresponds to C11 atomic_store_explicit(..., memory_order_release).
         */

        void putOrderedObject(Object o, long offset, Object x);

        /**
         * Ordered/Lazy version of {@link #putIntVolatile(Object, long, int)}
         */

        void putOrderedInt(Object o, long offset, int x);

        /**
         * Ordered/Lazy version of {@link #putLongVolatile(Object, long, long)}
         */

        void putOrderedLong(Object o, long offset, long x);

        /**
         * Unblocks the given thread blocked on {@code park}, or, if it is
         * not blocked, causes the subsequent call to {@code park} not to
         * block.  Note: this operation is "unsafe" solely because the
         * caller must somehow ensure that the thread has not been
         * destroyed. Nothing special is usually required to ensure this
         * when called from Java (in which there will ordinarily be a live
         * reference to the thread) but this is not nearly-automatically
         * so when calling from native code.
         *
         * @param thread the thread to unpark.
         */

        void unpark(Object thread);

        /**
         * Blocks current thread, returning when a balancing
         * {@code unpark} occurs, or a balancing {@code unpark} has
         * already occurred, or the thread is interrupted, or, if not
         * absolute and time is not zero, the given time nanoseconds have
         * elapsed, or if absolute, the given deadline in milliseconds
         * since Epoch has passed, or spuriously (i.e., returning for no
         * "reason"). Note: This operation is in the Unsafe class only
         * because {@code unpark} is, so it would be strange to place it
         * elsewhere.
         */

        void park(boolean isAbsolute, long time);

        /**
         * Gets the load average in the system run queue assigned
         * to the available processors averaged over various periods of time.
         * This method retrieves the given {@code nelem} samples and
         * assigns to the elements of the given {@code loadavg} array.
         * The system imposes a maximum of 3 samples, representing
         * averages over the last 1,  5,  and  15 minutes, respectively.
         *
         * @param loadavg an array of double of size nelems
         * @param nelems  the number of samples to be retrieved and
         *                must be 1 to 3.
         * @return the number of samples actually retrieved; or -1
         * if the load average is unobtainable.
         */

        int getLoadAverage(double[] loadavg, int nelems);

        // The following contain CAS-based Java implementations used on
        // platforms not supporting native instructions

        /**
         * Atomically adds the given value to the current value of a field
         * or array element within the given object {@code o}
         * at the given {@code offset}.
         *
         * @param o      object/array to update the field/element in
         * @param offset field/element offset
         * @param delta  the value to add
         * @return the previous value
         * @since 1.8
         */

        int getAndAddInt(Object o, long offset, int delta);

        /**
         * Atomically adds the given value to the current value of a field
         * or array element within the given object {@code o}
         * at the given {@code offset}.
         *
         * @param o      object/array to update the field/element in
         * @param offset field/element offset
         * @param delta  the value to add
         * @return the previous value
         * @since 1.8
         */

        long getAndAddLong(Object o, long offset, long delta);

        /**
         * Atomically exchanges the given value with the current value of
         * a field or array element within the given object {@code o}
         * at the given {@code offset}.
         *
         * @param o        object/array to update the field/element in
         * @param offset   field/element offset
         * @param newValue new value
         * @return the previous value
         * @since 1.8
         */

        int getAndSetInt(Object o, long offset, int newValue);

        /**
         * Atomically exchanges the given value with the current value of
         * a field or array element within the given object {@code o}
         * at the given {@code offset}.
         *
         * @param o        object/array to update the field/element in
         * @param offset   field/element offset
         * @param newValue new value
         * @return the previous value
         * @since 1.8
         */

        long getAndSetLong(Object o, long offset, long newValue);

        /**
         * Atomically exchanges the given reference value with the current
         * reference value of a field or array element within the given
         * object {@code o} at the given {@code offset}.
         *
         * @param o        object/array to update the field/element in
         * @param offset   field/element offset
         * @param newValue new value
         * @return the previous value
         * @since 1.8
         */

        Object getAndSetObject(Object o, long offset, Object newValue);


        /**
         * Ensures that loads before the fence will not be reordered with loads and
         * stores after the fence; a "LoadLoad plus LoadStore barrier".
         * <p>
         * Corresponds to C11 atomic_thread_fence(memory_order_acquire)
         * (an "acquire fence").
         * <p>
         * A pure LoadLoad fence is not provided, since the addition of LoadStore
         * is almost always desired, and most current hardware instructions that
         * provide a LoadLoad barrier also provide a LoadStore barrier for free.
         *
         * @since 1.8
         */

        void loadFence();

        /**
         * Ensures that loads and stores before the fence will not be reordered with
         * stores after the fence; a "StoreStore plus LoadStore barrier".
         * <p>
         * Corresponds to C11 atomic_thread_fence(memory_order_release)
         * (a "release fence").
         * <p>
         * A pure StoreStore fence is not provided, since the addition of LoadStore
         * is almost always desired, and most current hardware instructions that
         * provide a StoreStore barrier also provide a LoadStore barrier for free.
         *
         * @since 1.8
         */

        void storeFence();

        /**
         * Ensures that loads and stores before the fence will not be reordered
         * with loads and stores after the fence.  Implies the effects of both
         * loadFence() and storeFence(), and in addition, the effect of a StoreLoad
         * barrier.
         * <p>
         * Corresponds to C11 atomic_thread_fence(memory_order_seq_cst).
         *
         * @since 1.8
         */

        void fullFence();

        /**
         * Invokes the given direct byte buffer's cleaner, if any.
         *
         * @param directBuffer a direct byte buffer
         * @throws NullPointerException     if {@code directBuffer} is null
         * @throws IllegalArgumentException if {@code directBuffer} is non-direct,
         *                                  or is a {@link java.nio.Buffer#slice slice}, or is a
         *                                  {@link java.nio.Buffer#duplicate duplicate}
         * @since 9
         */
        void invokeCleaner(java.nio.ByteBuffer directBuffer);
    }

}