/*
 * Copyright (c) 2012, 2017, 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.
 *
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package com.oracle.svm.core.annotate;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import com.oracle.svm.core.hub.DynamicHub;

Defines that the annotated class should have a Hybrid layout. Hybrid layouts are hybrids between
instance layouts and array layouts. The contents of a specified member array and (optional)
member type id slots are directly placed within the class layout. This saves one indirection when
accessing the array or type id slots.

The array length is located directly after the HUB pointer, like in regular array. Then (if
present) the type id slots follow. Then the instance fields are placed. Then, with the default
GC, there is an optional identity hashcode. At the end of the layout, the array elements are
located.
   +--------------------------------+
   | pointer to DynamicHub          |
   +--------------------------------+
   | Array length                   |
   +--------------------------------+
   | type id slots (optional)|
   |     ...                        |
   +--------------------------------+
   | instance fields                |
   |     ...                        |
   +--------------------------------+
   | identity hashcode (optional)   |
   +--------------------------------+
   | array elements                 |
   :     ...                        :
 Currently only the DynamicHub class has a hybrid layout. /**
 * Defines that the annotated class should have a Hybrid layout. Hybrid layouts are hybrids between
 * instance layouts and array layouts. The contents of a specified member array and (optional)
 * member type id slots are directly placed within the class layout. This saves one indirection when
 * accessing the array or type id slots.
 *
 * <p>
 * The array length is located directly after the HUB pointer, like in regular array. Then (if
 * present) the type id slots follow. Then the instance fields are placed. Then, with the default
 * GC, there is an optional identity hashcode. At the end of the layout, the array elements are
 * located.
 * 
 * <pre>
 *    +--------------------------------+
 *    | pointer to DynamicHub          |
 *    +--------------------------------+
 *    | Array length                   |
 *    +--------------------------------+
 *    | type id slots (optional)|
 *    |     ...                        |
 *    +--------------------------------+
 *    | instance fields                |
 *    |     ...                        |
 *    +--------------------------------+
 *    | identity hashcode (optional)   |
 *    +--------------------------------+
 *    | array elements                 |
 *    :     ...                        :
 * </pre>
 * 
 * Currently only the {@link DynamicHub} class has a hybrid layout.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Hybrid {

    
Specifies a single member array as the hybrid array.
/**
     * Specifies a single member array as the hybrid array.
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    public @interface Array {
    }

    
Specifies a single member type slots.
/**
     * Specifies a single member type slots.
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    public @interface TypeIDSlots {
    }
}