1 /*
   2  * Copyright (c) 2019, Red Hat Inc. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.internal.misc;
  27 
  28 /**
  29  * A class used to expose details of the underlying hardware that
  30  * configure the operation of class Unsafe.  This class is
  31  * package-protected as the only intended client is class Unsafe.
  32  *
  33  * @since 13
  34  *
  35  * @implNote
  36 
  37  * The JVM injects values into all the static fields of this class
  38  * during JVM initialization. A static initialization block is used to
  39  * initialize these values but that is only done to communicate that
  40  * each static final field is not statically foldable, and to avoid
  41  * any possible circular dependency during vm initialization. The
  42  * values assigned in the static block may not correspond to the
  43  * hardware-specific constants installed by the JVM.
  44  */
  45 
  46 final class UnsafeConstants {
  47 
  48     /**
  49      * This constructor is private because the class is not meant to
  50      * be instantiated.
  51      */
  52     private UnsafeConstants() {}
  53 
  54     /**
  55      * The size in bytes of a native pointer, as stored via {@link
  56      * #putAddress}.  This value will be either 4 or 8.  Note that the
  57      * sizes of other primitive types (as stored in native memory
  58      * blocks) is determined fully by their information content.
  59      *
  60      * @implNote
  61      * The actual value for this field is injected by JVM. A static
  62      * initialization block is used to set the value here to
  63      * communicate that this static final field is not statically
  64      * foldable, and to avoid any possible circular dependency during
  65      * vm initialization.
  66      */
  67 
  68     static final int ADDRESS_SIZE;
  69 
  70     /**
  71      * The size in bytes of a native memory page (whatever that is).
  72      * This value will always be a power of two.
  73      *
  74      * @implNote
  75      * The actual value for this field is injected by JVM. A static
  76      * initialization block is used to set the value here to
  77      * communicate that this static final field is not statically
  78      * foldable, and to avoid any possible circular dependency during
  79      * vm initialization.
  80      */
  81 
  82     static final int PAGE_SIZE;
  83     
  84     /**
  85      * flag whose value is true if and only if the native endianness
  86      * of this platform is big.
  87      */
  88     
  89     static final boolean BIG_ENDIAN;
  90 
  91     /**
  92      * flag whose value is true if and only if the platform can
  93      * perform unaligned accesses
  94      */
  95     
  96     static final boolean UNALIGNED_ACCESS;
  97 
  98     static {
  99         ADDRESS_SIZE = 0;
 100         PAGE_SIZE = 0;
 101         BIG_ENDIAN = false;
 102         UNALIGNED_ACCESS = false;
 103     }
 104 }