Java tutorial
/** * Copyright The Apache Software Foundation * * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF 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.apache.hadoop.hbase.util; import java.lang.reflect.Field; import java.lang.reflect.Modifier; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentSkipListMap; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; /** * Class for determining the "size" of a class, an attempt to calculate the * actual bytes that an object of this class will occupy in memory * * The core of this class is taken from the Derby project */ @InterfaceAudience.Private public class ClassSize { static final Log LOG = LogFactory.getLog(ClassSize.class); private static int nrOfRefsPerObj = 2; /** Array overhead */ public static final int ARRAY; /** Overhead for ArrayList(0) */ public static final int ARRAYLIST; /** Overhead for ByteBuffer */ public static final int BYTE_BUFFER; /** Overhead for an Integer */ public static final int INTEGER; /** Overhead for entry in map */ public static final int MAP_ENTRY; /** Object overhead is minimum 2 * reference size (8 bytes on 64-bit) */ public static final int OBJECT; /** Reference size is 8 bytes on 64-bit, 4 bytes on 32-bit */ public static final int REFERENCE; /** String overhead */ public static final int STRING; /** Overhead for TreeMap */ public static final int TREEMAP; /** Overhead for ConcurrentHashMap */ public static final int CONCURRENT_HASHMAP; /** Overhead for ConcurrentHashMap.Entry */ public static final int CONCURRENT_HASHMAP_ENTRY; /** Overhead for ConcurrentHashMap.Segment */ public static final int CONCURRENT_HASHMAP_SEGMENT; /** Overhead for ConcurrentSkipListMap */ public static final int CONCURRENT_SKIPLISTMAP; /** Overhead for ConcurrentSkipListMap Entry */ public static final int CONCURRENT_SKIPLISTMAP_ENTRY; /** Overhead for ReentrantReadWriteLock */ public static final int REENTRANT_LOCK; /** Overhead for AtomicLong */ public static final int ATOMIC_LONG; /** Overhead for AtomicInteger */ public static final int ATOMIC_INTEGER; /** Overhead for AtomicBoolean */ public static final int ATOMIC_BOOLEAN; /** Overhead for CopyOnWriteArraySet */ public static final int COPYONWRITE_ARRAYSET; /** Overhead for CopyOnWriteArrayList */ public static final int COPYONWRITE_ARRAYLIST; /** Overhead for timerange */ public static final int TIMERANGE; /** Overhead for TimeRangeTracker */ public static final int TIMERANGE_TRACKER; /** Overhead for KeyValueSkipListSet */ public static final int KEYVALUE_SKIPLIST_SET; /* Are we running on jdk7? */ private static final boolean JDK7; static { final String version = System.getProperty("java.version"); // Verify String looks like this: 1.6.0_29 if (!version.matches("\\d\\.\\d\\..*")) { throw new RuntimeException("Unexpected version format: " + version); } // Convert char to int int major = (int) (version.charAt(0) - '0'); int minor = (int) (version.charAt(2) - '0'); JDK7 = major == 1 && minor == 7; } /** * Method for reading the arc settings and setting overheads according * to 32-bit or 64-bit architecture. */ static { //Default value is set to 8, covering the case when arcModel is unknown if (is32BitJVM()) { REFERENCE = 4; } else { REFERENCE = 8; } OBJECT = 2 * REFERENCE; ARRAY = align(3 * REFERENCE); ARRAYLIST = align(OBJECT + align(REFERENCE) + align(ARRAY) + (2 * Bytes.SIZEOF_INT)); //noinspection PointlessArithmeticExpression BYTE_BUFFER = align(OBJECT + align(REFERENCE) + align(ARRAY) + (5 * Bytes.SIZEOF_INT) + (3 * Bytes.SIZEOF_BOOLEAN) + Bytes.SIZEOF_LONG); INTEGER = align(OBJECT + Bytes.SIZEOF_INT); MAP_ENTRY = align(OBJECT + 5 * REFERENCE + Bytes.SIZEOF_BOOLEAN); TREEMAP = align(OBJECT + (2 * Bytes.SIZEOF_INT) + align(7 * REFERENCE)); // STRING is different size in jdk6 and jdk7. Just use what we estimate as size rather than // have a conditional on whether jdk7. STRING = (int) estimateBase(String.class, false); // CONCURRENT_HASHMAP is different size in jdk6 and jdk7; it looks like its different between // 23.6-b03 and 23.0-b21. Just use what we estimate as size rather than have a conditional on // whether jdk7. CONCURRENT_HASHMAP = (int) estimateBase(ConcurrentHashMap.class, false); CONCURRENT_HASHMAP_ENTRY = align(REFERENCE + OBJECT + (3 * REFERENCE) + (2 * Bytes.SIZEOF_INT)); CONCURRENT_HASHMAP_SEGMENT = align( REFERENCE + OBJECT + (3 * Bytes.SIZEOF_INT) + Bytes.SIZEOF_FLOAT + ARRAY); // The size changes from jdk7 to jdk8, estimate the size rather than use a conditional CONCURRENT_SKIPLISTMAP = (int) estimateBase(ConcurrentSkipListMap.class, false); CONCURRENT_SKIPLISTMAP_ENTRY = align(align(OBJECT + (3 * REFERENCE)) + /* one node per entry */ align((OBJECT + (3 * REFERENCE)) / 2)); /* one index per two entries */ REENTRANT_LOCK = align(OBJECT + (3 * REFERENCE)); ATOMIC_LONG = align(OBJECT + Bytes.SIZEOF_LONG); ATOMIC_INTEGER = align(OBJECT + Bytes.SIZEOF_INT); ATOMIC_BOOLEAN = align(OBJECT + Bytes.SIZEOF_BOOLEAN); COPYONWRITE_ARRAYSET = align(OBJECT + REFERENCE); COPYONWRITE_ARRAYLIST = align(OBJECT + (2 * REFERENCE) + ARRAY); TIMERANGE = align(ClassSize.OBJECT + Bytes.SIZEOF_LONG * 2 + Bytes.SIZEOF_BOOLEAN); TIMERANGE_TRACKER = align(ClassSize.OBJECT + Bytes.SIZEOF_LONG * 2); KEYVALUE_SKIPLIST_SET = align(OBJECT + REFERENCE); } /** * The estimate of the size of a class instance depends on whether the JVM * uses 32 or 64 bit addresses, that is it depends on the size of an object * reference. It is a linear function of the size of a reference, e.g. * 24 + 5*r where r is the size of a reference (usually 4 or 8 bytes). * * This method returns the coefficients of the linear function, e.g. {24, 5} * in the above example. * * @param cl A class whose instance size is to be estimated * @param debug debug flag * @return an array of 3 integers. The first integer is the size of the * primitives, the second the number of arrays and the third the number of * references. */ @SuppressWarnings("unchecked") private static int[] getSizeCoefficients(Class cl, boolean debug) { int primitives = 0; int arrays = 0; //The number of references that a new object takes int references = nrOfRefsPerObj; int index = 0; for (; null != cl; cl = cl.getSuperclass()) { Field[] field = cl.getDeclaredFields(); if (null != field) { for (Field aField : field) { if (Modifier.isStatic(aField.getModifiers())) continue; Class fieldClass = aField.getType(); if (fieldClass.isArray()) { arrays++; references++; } else if (!fieldClass.isPrimitive()) { references++; } else {// Is simple primitive String name = fieldClass.getName(); if (name.equals("int") || name.equals("I")) primitives += Bytes.SIZEOF_INT; else if (name.equals("long") || name.equals("J")) primitives += Bytes.SIZEOF_LONG; else if (name.equals("boolean") || name.equals("Z")) primitives += Bytes.SIZEOF_BOOLEAN; else if (name.equals("short") || name.equals("S")) primitives += Bytes.SIZEOF_SHORT; else if (name.equals("byte") || name.equals("B")) primitives += Bytes.SIZEOF_BYTE; else if (name.equals("char") || name.equals("C")) primitives += Bytes.SIZEOF_CHAR; else if (name.equals("float") || name.equals("F")) primitives += Bytes.SIZEOF_FLOAT; else if (name.equals("double") || name.equals("D")) primitives += Bytes.SIZEOF_DOUBLE; } if (debug) { if (LOG.isDebugEnabled()) { LOG.debug("" + index + " " + aField.getName() + " " + aField.getType()); } } index++; } } } return new int[] { primitives, arrays, references }; } /** * Estimate the static space taken up by a class instance given the * coefficients returned by getSizeCoefficients. * * @param coeff the coefficients * * @param debug debug flag * @return the size estimate, in bytes */ private static long estimateBaseFromCoefficients(int[] coeff, boolean debug) { long prealign_size = coeff[0] + align(coeff[1] * ARRAY) + coeff[2] * REFERENCE; // Round up to a multiple of 8 long size = align(prealign_size); if (debug) { if (LOG.isDebugEnabled()) { LOG.debug("Primitives=" + coeff[0] + ", arrays=" + coeff[1] + ", references(includes " + nrOfRefsPerObj + " for object overhead)=" + coeff[2] + ", refSize " + REFERENCE + ", size=" + size + ", prealign_size=" + prealign_size); } } return size; } /** * Estimate the static space taken up by the fields of a class. This includes * the space taken up by by references (the pointer) but not by the referenced * object. So the estimated size of an array field does not depend on the size * of the array. Similarly the size of an object (reference) field does not * depend on the object. * * @param cl class * @param debug debug flag * @return the size estimate in bytes. */ @SuppressWarnings("unchecked") public static long estimateBase(Class cl, boolean debug) { return estimateBaseFromCoefficients(getSizeCoefficients(cl, debug), debug); } /** * Aligns a number to 8. * @param num number to align to 8 * @return smallest number >= input that is a multiple of 8 */ public static int align(int num) { return (int) (align((long) num)); } /** * Aligns a number to 8. * @param num number to align to 8 * @return smallest number >= input that is a multiple of 8 */ public static long align(long num) { //The 7 comes from that the alignSize is 8 which is the number of bytes //stored and sent together return ((num + 7) >> 3) << 3; } /** * Determines if we are running in a 32-bit JVM. Some unit tests need to * know this too. */ public static boolean is32BitJVM() { return System.getProperty("sun.arch.data.model").equals("32"); } }