| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.iapi.services.cache.ClassSize |
| 4 | |
| 5 | Copyright 2002, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.iapi.services.cache; |
| 22 | |
| 23 | import org.apache.derby.iapi.services.sanity.SanityManager; |
| 24 | |
| 25 | import java.lang.Class; |
| 26 | import java.lang.reflect.Field; |
| 27 | import java.lang.Runtime; |
| 28 | import java.lang.InterruptedException; |
| 29 | import java.lang.reflect.Modifier; |
| 30 | |
| 31 | public class ClassSize |
| 32 | { |
| 33 | public static final int refSize; |
| 34 | private static final int objectOverhead = 2; // references, not bytes! |
| 35 | private static final int booleanSize = 4; |
| 36 | private static final int charSize = 4; // Unicode |
| 37 | private static final int shortSize = 4; |
| 38 | private static final int intSize = 4; |
| 39 | private static final int longSize = 8; |
| 40 | private static final int floatSize = 4; |
| 41 | private static final int doubleSize = 8; |
| 42 | private static final int minObjectSize; |
| 43 | |
| 44 | private static boolean dummyCatalog = false; // Used when constructing the catalog to prevent recursion |
| 45 | |
| 46 | static boolean noGuess = false; |
| 47 | // noGuess is used in unit testing. |
| 48 | |
| 49 | static boolean unitTest = false; |
| 50 | // unitTest is used in unit testing |
| 51 | |
| 52 | private static final int[] wildGuess = {0,16}; |
| 53 | /* The standard wild guess of the size of an unknown class, the size of 16 references. |
| 54 | * Used when the security manager will not let us look at the class fields. |
| 55 | */ |
| 56 | |
| 57 | /* Do not let the compiler see ClassSizeCatalog. Otherwise it will try to |
| 58 | * compile it. This may fail because ClassSizeCatalog.java is not created |
| 59 | * until everything else has been compiled. Bury ClassSizeCatalog in a string. |
| 60 | */ |
| 61 | private static java.util.Hashtable catalog; |
| 62 | static |
| 63 | { |
| 64 | try |
| 65 | { |
| 66 | catalog = (java.util.Hashtable) |
| 67 | Class.forName( "org.apache.derby.iapi.services.cache.ClassSizeCatalog").newInstance(); |
| 68 | } |
| 69 | catch( Exception e){}; |
| 70 | |
| 71 | // Figure out whether this is a 32 or 64 bit machine. |
| 72 | Runtime runtime = Runtime.getRuntime(); |
| 73 | long memBase = runtime.totalMemory() - runtime.freeMemory(); |
| 74 | Object[] junk = new Object[10000]; |
| 75 | long memUsed = runtime.totalMemory() - runtime.freeMemory() - memBase; |
| 76 | int sz = (int)((memUsed + junk.length/2)/junk.length); |
| 77 | refSize = ( 4 > sz) ? 4 : sz; |
| 78 | minObjectSize = 4*refSize; |
| 79 | } |
| 80 | |
| 81 | /** |
| 82 | * do not try to use the catalog. |
| 83 | */ |
| 84 | public static void setDummyCatalog() |
| 85 | { |
| 86 | dummyCatalog = true; |
| 87 | } |
| 88 | /** |
| 89 | * Get the estimate of the size of an object reference. |
| 90 | * |
| 91 | * @return the estimate in bytes. |
| 92 | */ |
| 93 | public static int getRefSize() |
| 94 | { |
| 95 | return refSize; |
| 96 | } |
| 97 | |
| 98 | /** |
| 99 | * @return the estimate of the size of a primitive int |
| 100 | */ |
| 101 | public static int getIntSize() |
| 102 | { |
| 103 | return intSize; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * The estimate of the size of a class instance depends on whether the JVM uses 32 or 64 |
| 108 | * bit addresses, that is it depends on the size of an object reference. It is a linear |
| 109 | * function of the size of a reference, e.g. |
| 110 | * 24 + 5*r |
| 111 | * where r is the size of a reference (usually 4 or 8 bytes). |
| 112 | * |
| 113 | * This method returns the coefficients of the linear function, e.g. {24, 5} in the above |
| 114 | * example. |
| 115 | * |
| 116 | * @param cl A class whose instance size is to be estimated |
| 117 | * @return an array of 2 integers. The first integer is the constant part of the function, |
| 118 | * the second is the reference size coefficient. |
| 119 | */ |
| 120 | public static int[] getSizeCoefficients( Class cl) |
| 121 | { |
| 122 | int[] coeff = {0, objectOverhead}; |
| 123 | |
| 124 | |
| 125 | |
| 126 | for( ; null != cl; cl = cl.getSuperclass()) |
| 127 | { |
| 128 | Field[] field = cl.getDeclaredFields(); |
| 129 | if( null != field) |
| 130 | { |
| 131 | for( int i = 0; i < field.length; i++) |
| 132 | { |
| 133 | if( ! Modifier.isStatic( field[i].getModifiers())) |
| 134 | { |
| 135 | Class fieldClass = field[i].getType(); |
| 136 | if( fieldClass.isArray() || ! fieldClass.isPrimitive()) |
| 137 | coeff[1]++; |
| 138 | else // Is simple primitive |
| 139 | { |
| 140 | String name = fieldClass.getName(); |
| 141 | |
| 142 | if( name.equals( "int") || name.equals( "I")) |
| 143 | coeff[0] += intSize; |
| 144 | else if( name.equals( "long") || name.equals( "J")) |
| 145 | coeff[0] += longSize; |
| 146 | else if( name.equals( "boolean") || name.equals( "Z")) |
| 147 | coeff[0] += booleanSize; |
| 148 | else if( name.equals( "short") || name.equals( "S")) |
| 149 | coeff[0] += shortSize; |
| 150 | else if( name.equals( "byte") || name.equals( "B")) |
| 151 | coeff[0] += 1; |
| 152 | else if( name.equals( "char") || name.equals( "C")) |
| 153 | coeff[0] += charSize; |
| 154 | else if( name.equals( "float") || name.equals( "F")) |
| 155 | coeff[0] += floatSize; |
| 156 | else if( name.equals( "double") || name.equals( "D")) |
| 157 | coeff[0] += doubleSize; |
| 158 | else // What is this?? |
| 159 | coeff[1]++; // Make a guess: one reference (?) |
| 160 | } |
| 161 | } |
| 162 | } |
| 163 | } |
| 164 | } |
| 165 | return coeff; |
| 166 | } // end of getSizeCoefficients |
| 167 | |
| 168 | /** |
| 169 | * Estimate the static space taken up by a class instance given the coefficients |
| 170 | * returned by getSizeCoefficients. |
| 171 | * |
| 172 | * @param coeff the coefficients |
| 173 | * |
| 174 | * @return the size estimate, in bytes |
| 175 | */ |
| 176 | public static int estimateBaseFromCoefficients( int[] coeff) |
| 177 | { |
| 178 | int size = coeff[0] + coeff[1]*refSize; |
| 179 | // Round up to a multiple of 8 |
| 180 | size = (size + 7)/8; |
| 181 | size *= 8; |
| 182 | return (size < minObjectSize) ? minObjectSize : size; |
| 183 | } // end of estimateBaseFromCoefficients |
| 184 | |
| 185 | /** |
| 186 | * Estimate the static space taken up by a class instance from cataloged coefficients. |
| 187 | * |
| 188 | * @param cls the class |
| 189 | * |
| 190 | * @return the size estimate, in bytes |
| 191 | * |
| 192 | * @see #estimateBaseFromCoefficients |
| 193 | * @see #getSizeCoefficients |
| 194 | * see org.apache.derbyBuild.ClassSizeCrawler |
| 195 | */ |
| 196 | public static int estimateBaseFromCatalog( Class cls) |
| 197 | { |
| 198 | return estimateBaseFromCatalog( cls, false); |
| 199 | } |
| 200 | |
| 201 | private static int estimateBaseFromCatalog( Class cls, boolean addToCatalog) |
| 202 | { |
| 203 | if( dummyCatalog) |
| 204 | return 0; |
| 205 | |
| 206 | if( SanityManager.DEBUG) |
| 207 | SanityManager.ASSERT( catalog != null, "The class size catalog could not be initialized."); |
| 208 | |
| 209 | int[] coeff = (int[]) catalog.get( cls.getName()); |
| 210 | if( coeff == null) |
| 211 | { |
| 212 | try |
| 213 | { |
| 214 | coeff = getSizeCoefficients( cls); |
| 215 | } |
| 216 | catch( Throwable t) |
| 217 | { |
| 218 | if( noGuess) |
| 219 | return -2; |
| 220 | coeff = wildGuess; |
| 221 | } |
| 222 | if( addToCatalog) |
| 223 | catalog.put( cls.getName(), coeff); |
| 224 | } |
| 225 | return estimateBaseFromCoefficients( coeff); |
| 226 | } // end of estimateBaseFromCatalog |
| 227 | |
| 228 | |
| 229 | /** |
| 230 | * Estimate the static space taken up by a class instance. Save the coefficients |
| 231 | * in a catalog. |
| 232 | * |
| 233 | * @param cls the class |
| 234 | * |
| 235 | * @return the size estimate, in bytes |
| 236 | * |
| 237 | * @see #estimateBaseFromCoefficients |
| 238 | * @see #getSizeCoefficients |
| 239 | * see org.apache.derbyBuild.ClassSizeCrawler |
| 240 | */ |
| 241 | public static int estimateAndCatalogBase( Class cls) |
| 242 | { |
| 243 | return estimateBaseFromCatalog( cls, true); |
| 244 | } // end of estimateAndCatalogBase |
| 245 | |
| 246 | /** |
| 247 | * Estimate the static space taken up by the fields of a class. This includes the space taken |
| 248 | * up by by references (the pointer) but not by the referenced object. So the estimated |
| 249 | * size of an array field does not depend on the size of the array. Similarly the size of |
| 250 | * an object (reference) field does not depend on the object. |
| 251 | * |
| 252 | * @return the size estimate in bytes. |
| 253 | * |
| 254 | * Note that this method will throw a SecurityException if the SecurityManager does not |
| 255 | * let this class execute the method Class.getDeclaredFields(). If this is a concern try |
| 256 | * to compute the size coefficients at build time. |
| 257 | * see org.apache.derbyBuild.ClassSizeCrawler |
| 258 | * @see #estimateBaseFromCatalog |
| 259 | */ |
| 260 | public static int estimateBase( Class cl) |
| 261 | { |
| 262 | return estimateBaseFromCoefficients( getSizeCoefficients( cl)); |
| 263 | } // End of estimateBase |
| 264 | |
| 265 | /** |
| 266 | * @return the estimated overhead of an array. The estimated size of an x[n] array is |
| 267 | * estimateArrayOverhead() + n*sizeOf(x). |
| 268 | */ |
| 269 | public static int estimateArrayOverhead() |
| 270 | { |
| 271 | return minObjectSize; |
| 272 | } |
| 273 | |
| 274 | /** |
| 275 | * Estimate the size of a Hashtable entry. In Java 1.2 we can use Map.entry, but this is not |
| 276 | * available in earlier versions of Java. |
| 277 | * |
| 278 | * @return the estimate, in bytes |
| 279 | */ |
| 280 | public static int estimateHashEntrySize() |
| 281 | { |
| 282 | return objectOverhead + 3*refSize; |
| 283 | } |
| 284 | |
| 285 | /** |
| 286 | * Estimate the size of a string. |
| 287 | * |
| 288 | * @return the estimated size, in bytes |
| 289 | */ |
| 290 | public static int estimateMemoryUsage( String str) |
| 291 | { |
| 292 | if( null == str) |
| 293 | return 0; |
| 294 | // Since Java uses Unicode assume that each character takes 2 bytes |
| 295 | return 2*str.length(); |
| 296 | } |
| 297 | } |