MemoryLayoutSpecification.java

/*
 * Copyright (c) 2016, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
 *
 * WSO2 Inc. licenses this file to you under the Apache License,
 * Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.wso2.siddhi.core.util.statistics.memory;

/**
 * Describes constant memory overheads for various constructs in a JVM implementation.
 */
public interface MemoryLayoutSpecification {

    /**
     * Returns the fixed overhead of an array of any type or length in this JVM.
     *
     * @return the fixed overhead of an array.
     */
    int getArrayHeaderSize();

    /**
     * Returns the fixed overhead of for any {@link Object} subclass in this JVM.
     *
     * @return the fixed overhead of any object.
     */
    int getObjectHeaderSize();

    /**
     * Returns the quantum field size for a field owned by an object in this JVM.
     *
     * @return the quantum field size for an object.
     */
    int getObjectPadding();

    /**
     * Returns the fixed size of an object reference in this JVM.
     *
     * @return the size of all object references.
     */
    int getReferenceSize();

    /**
     * Returns the quantum field size for a field owned by one of an object's ancestor superclasses
     * in this JVM.
     *
     * @return the quantum field size for a superclass field.
     */
    int getSuperclassFieldPadding();
}