/*

 * Copyright (c) 2000, 2015, 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).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.internal.misc;

import java.lang.reflect.Field;

import java.security.ProtectionDomain;

import sun.reflect.CallerSensitive;

import sun.reflect.Reflection;

import jdk.internal.misc.VM;

import jdk.internal.HotSpotIntrinsicCandidate;

/**

 * A collection of methods for performing low-level, unsafe operations.

 * Although the class and all methods are public, use of this class is

 * limited because only trusted code can obtain instances of it.

 *

 * @author John R. Rose

 * @see #getUnsafe

 */

public final class Unsafe {

    private static native void registerNatives();

    static {

        registerNatives();

        sun.reflect.Reflection.registerMethodsToFilter(Unsafe.class, "getUnsafe");

    }

    private Unsafe() {}

    private static final Unsafe theUnsafe = new Unsafe();

    /**

     * 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>

     *

     * (It may assist compilers to make the local variable {@code final}.)

     *

     * @throws  SecurityException  if a security manager exists and its

     *          {@code checkPropertiesAccess} method doesn't allow

     *          access to the system properties.

     */

    @CallerSensitive

    public static Unsafe getUnsafe() {

        Class<?> caller = Reflection.getCallerClass();

        if (!VM.isSystemDomainLoader(caller.getClassLoader()))

            throw new SecurityException("Unsafe");

        return theUnsafe;

    }

    /// 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}

     */

    @HotSpotIntrinsicCandidate

    public native 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}

     */

    @HotSpotIntrinsicCandidate

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

    /**

     * Fetches a reference value from a given Java variable.

     * @see #getInt(Object, long)

     */

    @HotSpotIntrinsicCandidate

    public native 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)

     */

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native boolean getBoolean(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native byte    getByte(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native short   getShort(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native char    getChar(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native long    getLong(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native float   getFloat(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

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

    @HotSpotIntrinsicCandidate

    public native double  getDouble(Object o, long offset);

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

    @HotSpotIntrinsicCandidate

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

    // These read VM internal data.

    /**

     * Fetches an uncompressed reference value from a given native variable

     * ignoring the VM's compressed references mode.

     *

     * @param address a memory address locating the variable

     * @return the value fetched from the indicated native variable

     */

    public native Object getUncompressedObject(long address);

    /**

     * Fetches the {@link java.lang.Class} Java mirror for the given native

     * metaspace {@code Klass} pointer.

     *

     * @param metaspaceKlass a native metaspace {@code Klass} pointer

     * @return the {@link java.lang.Class} Java mirror

     */

    public native Class<?> getJavaMirror(long metaspaceKlass);

    /**

     * Fetches a native metaspace {@code Klass} pointer for the given Java

     * object.

     *

     * @param o Java heap object for which to fetch the class pointer

     * @return a native metaspace {@code Klass} pointer

     */

    public native long getKlassPointer(Object o);

    // 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

     */

    @HotSpotIntrinsicCandidate

    public native 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)

     */

    @HotSpotIntrinsicCandidate

    public native void    putByte(long address, byte x);

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

    @HotSpotIntrinsicCandidate

    public native short   getShort(long address);

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

    @HotSpotIntrinsicCandidate

    public native void    putShort(long address, short x);

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

    @HotSpotIntrinsicCandidate

    public native char    getChar(long address);

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

    @HotSpotIntrinsicCandidate

    public native void    putChar(long address, char x);

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

    @HotSpotIntrinsicCandidate

    public native int     getInt(long address);

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

    @HotSpotIntrinsicCandidate

    public native void    putInt(long address, int x);

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

    @HotSpotIntrinsicCandidate

    public native long    getLong(long address);

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

    @HotSpotIntrinsicCandidate

    public native void    putLong(long address, long x);

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

    @HotSpotIntrinsicCandidate

    public native float   getFloat(long address);

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

    @HotSpotIntrinsicCandidate

    public native void    putFloat(long address, float x);

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

    @HotSpotIntrinsicCandidate

    public native double  getDouble(long address);

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

    @HotSpotIntrinsicCandidate

    public native 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

     */

    @HotSpotIntrinsicCandidate

    public native 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)

     */

    @HotSpotIntrinsicCandidate

    public native 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}.

     *

     * @throws IllegalArgumentException 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)

     */

    public native 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.

     *

     * @throws IllegalArgumentException 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

     */

    public native 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'.

     *

     * @since 1.7

     */

    public native 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)}.

     */

    public void setMemory(long address, long bytes, byte value) {

        setMemory(null, address, bytes, 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'.

     *

     * @since 1.7

     */

    @HotSpotIntrinsicCandidate

    public native 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)}.

     *

     * Equivalent to {@code copyMemory(null, srcAddress, null, destAddress, bytes)}.

     */

    public void copyMemory(long srcAddress, long destAddress, long bytes) {

        copyMemory(null, srcAddress, null, destAddress, 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.

     *

     * @see #allocateMemory

     */

    public native void freeMemory(long address);

    /// random queries

    /**

     * This constant differs from all results that will ever be returned from

     * {@link #staticFieldOffset}, {@link #objectFieldOffset},

     * or {@link #arrayBaseOffset}.

     */

    public static final int INVALID_FIELD_OFFSET   = -1;

    /**

     * 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)

     */

    public native 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)

     */

    public native 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.

     */

    public native Object staticFieldBase(Field f);