JDK8/Java8源码在线阅读

/*
 * Copyright (c) 2000, 2002, 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 sun.nio.ch;                                     // Formerly in sun.misc

import java.nio.ByteOrder;
import sun.misc.Unsafe;


// ## In the fullness of time, this class will be eliminated

/**
 * Proxies for objects that reside in native memory.
 */

class NativeObject {                                    // package-private

    protected static final Unsafe unsafe = Unsafe.getUnsafe();

    // Native allocation address;
    // may be smaller than the base address due to page-size rounding
    //
    protected long allocationAddress;

    // Native base address
    //
    private final long address;

    /**
     * Creates a new native object that is based at the given native address.
     */
    NativeObject(long address) {
        this.allocationAddress = address;
        this.address = address;
    }

    /**
     * Creates a new native object allocated at the given native address but
     * whose base is at the additional offset.
     */
    NativeObject(long address, long offset) {
        this.allocationAddress = address;
        this.address = address + offset;
    }

    // Invoked only by AllocatedNativeObject
    //
    protected NativeObject(int size, boolean pageAligned) {
        if (!pageAligned) {
            this.allocationAddress = unsafe.allocateMemory(size);
            this.address = this.allocationAddress;
        } else {
            int ps = pageSize();
            long a = unsafe.allocateMemory(size + ps);
            this.allocationAddress = a;
            this.address = a + ps - (a & (ps - 1));
        }
    }

    /**
     * Returns the native base address of this native object.
     *
     * @return The native base address
     */
    long address() {
        return address;
    }

    long allocationAddress() {
        return allocationAddress;
    }

    /**
     * Creates a new native object starting at the given offset from the base
     * of this native object.
     *
     * @param  offset
     *         The offset from the base of this native object that is to be
     *         the base of the new native object
     *
     * @return The newly created native object
     */
    NativeObject subObject(int offset) {
        return new NativeObject(offset + address);
    }

    /**
     * Reads an address from this native object at the given offset and
     * constructs a native object using that address.
     *
     * @param  offset
     *         The offset of the address to be read.  Note that the size of an
     *         address is implementation-dependent.
     *
     * @return The native object created using the address read from the
     *         given offset
     */
    NativeObject getObject(int offset) {
        long newAddress = 0L;
        switch (addressSize()) {
            case 8:
                newAddress = unsafe.getLong(offset + address);
                break;
            case 4:
                newAddress = unsafe.getInt(offset + address) & 0x00000000FFFFFFFF;
                break;
            default:
                throw new InternalError("Address size not supported");
        }

        return new NativeObject(newAddress);
    }

    /**
     * Writes the base address of the given native object at the given offset
     * of this native object.
     *
     * @param  offset
     *         The offset at which the address is to be written.  Note that the
     *         size of an address is implementation-dependent.
     *
     * @param  ob
     *         The native object whose address is to be written
     */
    void putObject(int offset, NativeObject ob) {
        switch (addressSize()) {
            case 8:
                putLong(offset, ob.address);
                break;
            case 4:
                putInt(offset, (int)(ob.address & 0x00000000FFFFFFFF));
                break;
            default:
                throw new InternalError("Address size not supported");
        }
    }


    /* -- Value accessors: No range checking! -- */

    /**
     * Reads a byte starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the byte
     *
     * @return The byte value read
     */
    final byte getByte(int offset) {
        return unsafe.getByte(offset + address);
    }

    /**
     * Writes a byte at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the byte
     *
     * @param  value
     *         The byte value to be written
     */
    final void putByte(int offset, byte value) {
        unsafe.putByte(offset + address,  value);
    }

    /**
     * Reads a short starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the short
     *
     * @return The short value read
     */
    final short getShort(int offset) {
        return unsafe.getShort(offset + address);
    }

    /**
     * Writes a short at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the short
     *
     * @param  value
     *         The short value to be written
     */
    final void putShort(int offset, short value) {
        unsafe.putShort(offset + address,  value);
    }

    /**
     * Reads a char starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the char
     *
     * @return The char value read
     */
    final char getChar(int offset) {
        return unsafe.getChar(offset + address);
    }

    /**
     * Writes a char at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the char
     *
     * @param  value
     *         The char value to be written
     */
    final void putChar(int offset, char value) {
        unsafe.putChar(offset + address,  value);
    }

    /**
     * Reads an int starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the int
     *
     * @return The int value read
     */
    final int getInt(int offset) {
        return unsafe.getInt(offset + address);
    }

    /**
     * Writes an int at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the int
     *
     * @param  value
     *         The int value to be written
     */
    final void putInt(int offset, int value) {
        unsafe.putInt(offset + address, value);
    }

    /**
     * Reads a long starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the long
     *
     * @return The long value read
     */
    final long getLong(int offset) {
        return unsafe.getLong(offset + address);
    }

    /**
     * Writes a long at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the long
     *
     * @param  value
     *         The long value to be written
     */
    final void putLong(int offset, long value) {
        unsafe.putLong(offset + address, value);
    }

    /**
     * Reads a float starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the float
     *
     * @return The float value read
     */
    final float getFloat(int offset) {
        return unsafe.getFloat(offset + address);
    }

    /**
     * Writes a float at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the float
     *
     * @param  value
     *         The float value to be written
     */
    final void putFloat(int offset, float value) {
        unsafe.putFloat(offset + address, value);
    }

    /**
     * Reads a double starting at the given offset from base of this native
     * object.
     *
     * @param  offset
     *         The offset at which to read the double
     *
     * @return The double value read
     */
    final double getDouble(int offset) {
        return unsafe.getDouble(offset + address);
    }

    /**
     * Writes a double at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the double
     *
     * @param  value
     *         The double value to be written
     */
    final void putDouble(int offset, double value) {
        unsafe.putDouble(offset + address, value);
    }

    /**
     * Returns the native architecture's address size in bytes.
     *
     * @return The address size of the native architecture
     */
    static int addressSize() {

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