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| 1 | /* | ||
| 2 | * Copyright (c) 2003, 2008, Oracle and/or its affiliates. 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 java.lang.management; | ||
| 27 | |||
| 28 | import javax.management.openmbean.CompositeData; | ||
| 29 | |||
| 30 | /** | ||
| 31 | * The management interface for the memory system of | ||
| 32 | * the Java virtual machine. | ||
| 33 | * | ||
| 34 | * <p> A Java virtual machine has a single instance of the implementation | ||
| 35 | * class of this interface. This instance implementing this interface is | ||
| 36 | * an <a href="ManagementFactory.html#MXBean">MXBean</a> | ||
| 37 | * that can be obtained by calling | ||
| 38 | * the {@link ManagementFactory#getMemoryMXBean} method or | ||
| 39 | * from the {@link ManagementFactory#getPlatformMBeanServer | ||
| 40 | * platform <tt>MBeanServer</tt>} method. | ||
| 41 | * | ||
| 42 | * <p>The <tt>ObjectName</tt> for uniquely identifying the MXBean for | ||
| 43 | * the memory system within an MBeanServer is: | ||
| 44 | * <blockquote> | ||
| 45 | * {@link ManagementFactory#MEMORY_MXBEAN_NAME | ||
| 46 | * <tt>java.lang:type=Memory</tt>} | ||
| 47 | * </blockquote> | ||
| 48 | * | ||
| 49 | * It can be obtained by calling the | ||
| 50 | * {@link PlatformManagedObject#getObjectName} method. | ||
| 51 | * | ||
| 52 | * <h4> Memory </h4> | ||
| 53 | * The memory system of the Java virtual machine manages | ||
| 54 | * the following kinds of memory: | ||
| 55 | * | ||
| 56 | * <h4> 1. Heap </h4> | ||
| 57 | * The Java virtual machine has a <i>heap</i> that is the runtime | ||
| 58 | * data area from which memory for all class instances and arrays | ||
| 59 | * are allocated. It is created at the Java virtual machine start-up. | ||
| 60 | * Heap memory for objects is reclaimed by an automatic memory management | ||
| 61 | * system which is known as a <i>garbage collector</i>. | ||
| 62 | * | ||
| 63 | * <p>The heap may be of a fixed size or may be expanded and shrunk. | ||
| 64 | * The memory for the heap does not need to be contiguous. | ||
| 65 | * | ||
| 66 | * <h4> 2. Non-Heap Memory</h4> | ||
| 67 | * The Java virtual machine manages memory other than the heap | ||
| 68 | * (referred as <i>non-heap memory</i>). | ||
| 69 | * | ||
| 70 | * <p> The Java virtual machine has a <i>method area</i> that is shared | ||
| 71 | * among all threads. | ||
| 72 | * The method area belongs to non-heap memory. It stores per-class structures | ||
| 73 | * such as a runtime constant pool, field and method data, and the code for | ||
| 74 | * methods and constructors. It is created at the Java virtual machine | ||
| 75 | * start-up. | ||
| 76 | * | ||
| 77 | * <p> The method area is logically part of the heap but a Java virtual | ||
| 78 | * machine implementation may choose not to either garbage collect | ||
| 79 | * or compact it. Similar to the heap, the method area may be of a | ||
| 80 | * fixed size or may be expanded and shrunk. The memory for the | ||
| 81 | * method area does not need to be contiguous. | ||
| 82 | * | ||
| 83 | * <p>In addition to the method area, a Java virtual machine | ||
| 84 | * implementation may require memory for internal processing or | ||
| 85 | * optimization which also belongs to non-heap memory. | ||
| 86 | * For example, the JIT compiler requires memory for storing the native | ||
| 87 | * machine code translated from the Java virtual machine code for | ||
| 88 | * high performance. | ||
| 89 | * | ||
| 90 | * <h4>Memory Pools and Memory Managers</h4> | ||
| 91 | * {@link MemoryPoolMXBean Memory pools} and | ||
| 92 | * {@link MemoryManagerMXBean memory managers} are the abstract entities | ||
| 93 | * that monitor and manage the memory system | ||
| 94 | * of the Java virtual machine. | ||
| 95 | * | ||
| 96 | * <p>A memory pool represents a memory area that the Java virtual machine | ||
| 97 | * manages. The Java virtual machine has at least one memory pool | ||
| 98 | * and it may create or remove memory pools during execution. | ||
| 99 | * A memory pool can belong to either the heap or the non-heap memory. | ||
| 100 | * | ||
| 101 | * <p>A memory manager is responsible for managing one or more memory pools. | ||
| 102 | * The garbage collector is one type of memory manager responsible | ||
| 103 | * for reclaiming memory occupied by unreachable objects. A Java virtual | ||
| 104 | * machine may have one or more memory managers. It may | ||
| 105 | * add or remove memory managers during execution. | ||
| 106 | * A memory pool can be managed by more than one memory manager. | ||
| 107 | * | ||
| 108 | * <h4>Memory Usage Monitoring</h4> | ||
| 109 | * | ||
| 110 | * Memory usage is a very important monitoring attribute for the memory system. | ||
| 111 | * The memory usage, for example, could indicate: | ||
| 112 | * <ul> | ||
| 113 | * <li>the memory usage of an application,</li> | ||
| 114 | * <li>the workload being imposed on the automatic memory management system,</li> | ||
| 115 | * <li>potential memory leakage.</li> | ||
| 116 | * </ul> | ||
| 117 | * | ||
| 118 | * <p> | ||
| 119 | * The memory usage can be monitored in three ways: | ||
| 120 | * <ul> | ||
| 121 | * <li>Polling</li> | ||
| 122 | * <li>Usage Threshold Notification</li> | ||
| 123 | * <li>Collection Usage Threshold Notification</li> | ||
| 124 | * </ul> | ||
| 125 | * | ||
| 126 | * Details are specified in the {@link MemoryPoolMXBean} interface. | ||
| 127 | * | ||
| 128 | * <p>The memory usage monitoring mechanism is intended for load-balancing | ||
| 129 | * or workload distribution use. For example, an application would stop | ||
| 130 | * receiving any new workload when its memory usage exceeds a | ||
| 131 | * certain threshold. It is not intended for an application to detect | ||
| 132 | * and recover from a low memory condition. | ||
| 133 | * | ||
| 134 | * <h4>Notifications</h4> | ||
| 135 | * | ||
| 136 | * <p>This <tt>MemoryMXBean</tt> is a | ||
| 137 | * {@link javax.management.NotificationEmitter NotificationEmitter} | ||
| 138 | * that emits two types of memory {@link javax.management.Notification | ||
| 139 | * notifications} if any one of the memory pools | ||
| 140 | * supports a <a href="MemoryPoolMXBean.html#UsageThreshold">usage threshold</a> | ||
| 141 | * or a <a href="MemoryPoolMXBean.html#CollectionThreshold">collection usage | ||
| 142 | * threshold</a> which can be determined by calling the | ||
| 143 | * {@link MemoryPoolMXBean#isUsageThresholdSupported} and | ||
| 144 | * {@link MemoryPoolMXBean#isCollectionUsageThresholdSupported} methods. | ||
| 145 | * <ul> | ||
| 146 | * <li>{@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED | ||
| 147 | * usage threshold exceeded notification} - for notifying that | ||
| 148 | * the memory usage of a memory pool is increased and has reached | ||
| 149 | * or exceeded its | ||
| 150 | * <a href="MemoryPoolMXBean.html#UsageThreshold"> usage threshold</a> value. | ||
| 151 | * </li> | ||
| 152 | * <li>{@link MemoryNotificationInfo#MEMORY_COLLECTION_THRESHOLD_EXCEEDED | ||
| 153 | * collection usage threshold exceeded notification} - for notifying that | ||
| 154 | * the memory usage of a memory pool is greater than or equal to its | ||
| 155 | * <a href="MemoryPoolMXBean.html#CollectionThreshold"> | ||
| 156 | * collection usage threshold</a> after the Java virtual machine | ||
| 157 | * has expended effort in recycling unused objects in that | ||
| 158 | * memory pool.</li> | ||
| 159 | * </ul> | ||
| 160 | * | ||
| 161 | * <p> | ||
| 162 | * The notification emitted is a {@link javax.management.Notification} | ||
| 163 | * instance whose {@link javax.management.Notification#setUserData | ||
| 164 | * user data} is set to a {@link CompositeData CompositeData} | ||
| 165 | * that represents a {@link MemoryNotificationInfo} object | ||
| 166 | * containing information about the memory pool when the notification | ||
| 167 | * was constructed. The <tt>CompositeData</tt> contains the attributes | ||
| 168 | * as described in {@link MemoryNotificationInfo#from | ||
| 169 | * MemoryNotificationInfo}. | ||
| 170 | * | ||
| 171 | * <hr> | ||
| 172 | * <h4>NotificationEmitter</h4> | ||
| 173 | * The <tt>MemoryMXBean</tt> object returned by | ||
| 174 | * {@link ManagementFactory#getMemoryMXBean} implements | ||
| 175 | * the {@link javax.management.NotificationEmitter NotificationEmitter} | ||
| 176 | * interface that allows a listener to be registered within the | ||
| 177 | * <tt>MemoryMXBean</tt> as a notification listener. | ||
| 178 | * | ||
| 179 | * Below is an example code that registers a <tt>MyListener</tt> to handle | ||
| 180 | * notification emitted by the <tt>MemoryMXBean</tt>. | ||
| 181 | * | ||
| 182 | * <blockquote><pre> | ||
| 183 | * class MyListener implements javax.management.NotificationListener { | ||
| 184 | * public void handleNotification(Notification notif, Object handback) { | ||
| 185 | * // handle notification | ||
| 186 | * .... | ||
| 187 | * } | ||
| 188 | * } | ||
| 189 | * | ||
| 190 | * MemoryMXBean mbean = ManagementFactory.getMemoryMXBean(); | ||
| 191 | * NotificationEmitter emitter = (NotificationEmitter) mbean; | ||
| 192 | * MyListener listener = new MyListener(); | ||
| 193 | * emitter.addNotificationListener(listener, null, null); | ||
| 194 | * </pre></blockquote> | ||
| 195 | * | ||
| 196 | * @see ManagementFactory#getPlatformMXBeans(Class) | ||
| 197 | * @see <a href="../../../javax/management/package-summary.html"> | ||
| 198 | * JMX Specification.</a> | ||
| 199 | * @see <a href="package-summary.html#examples"> | ||
| 200 | * Ways to Access MXBeans</a> | ||
| 201 | * | ||
| 202 | * @author Mandy Chung | ||
| 203 | * @since 1.5 | ||
| 204 | */ | ||
| 205 | public interface MemoryMXBean extends PlatformManagedObject { | ||
| 206 | /** | ||
| 207 | * Returns the approximate number of objects for which | ||
| 208 | * finalization is pending. | ||
| 209 | * | ||
| 210 | * @return the approximate number objects for which finalization | ||
| 211 | * is pending. | ||
| 212 | */ | ||
| 213 | public int getObjectPendingFinalizationCount(); | ||
| 214 | |||
| 215 | /** | ||
| 216 | * Returns the current memory usage of the heap that | ||
| 217 | * is used for object allocation. The heap consists | ||
| 218 | * of one or more memory pools. The <tt>used</tt> | ||
| 219 | * and <tt>committed</tt> size of the returned memory | ||
| 220 | * usage is the sum of those values of all heap memory pools | ||
| 221 | * whereas the <tt>init</tt> and <tt>max</tt> size of the | ||
| 222 | * returned memory usage represents the setting of the heap | ||
| 223 | * memory which may not be the sum of those of all heap | ||
| 224 | * memory pools. | ||
| 225 | * <p> | ||
| 226 | * The amount of used memory in the returned memory usage | ||
| 227 | * is the amount of memory occupied by both live objects | ||
| 228 | * and garbage objects that have not been collected, if any. | ||
| 229 | * | ||
| 230 | * <p> | ||
| 231 | * <b>MBeanServer access</b>:<br> | ||
| 232 | * The mapped type of <tt>MemoryUsage</tt> is | ||
| 233 | * <tt>CompositeData</tt> with attributes as specified in | ||
| 234 | * {@link MemoryUsage#from MemoryUsage}. | ||
| 235 | * | ||
| 236 | * @return a {@link MemoryUsage} object representing | ||
| 237 | * the heap memory usage. | ||
| 238 | */ | ||
| 239 | public MemoryUsage getHeapMemoryUsage(); | ||
| 240 | |||
| 241 | /** | ||
| 242 | * Returns the current memory usage of non-heap memory that | ||
| 243 | * is used by the Java virtual machine. | ||
| 244 | * The non-heap memory consists of one or more memory pools. | ||
| 245 | * The <tt>used</tt> and <tt>committed</tt> size of the | ||
| 246 | * returned memory usage is the sum of those values of | ||
| 247 | * all non-heap memory pools whereas the <tt>init</tt> | ||
| 248 | * and <tt>max</tt> size of the returned memory usage | ||
| 249 | * represents the setting of the non-heap | ||
| 250 | * memory which may not be the sum of those of all non-heap | ||
| 251 | * memory pools. | ||
| 252 | * | ||
| 253 | * <p> | ||
| 254 | * <b>MBeanServer access</b>:<br> | ||
| 255 | * The mapped type of <tt>MemoryUsage</tt> is | ||
| 256 | * <tt>CompositeData</tt> with attributes as specified in | ||
| 257 | * {@link MemoryUsage#from MemoryUsage}. | ||
| 258 | * | ||
| 259 | * @return a {@link MemoryUsage} object representing | ||
| 260 | * the non-heap memory usage. | ||
| 261 | */ | ||
| 262 | public MemoryUsage getNonHeapMemoryUsage(); | ||
| 263 | |||
| 264 | /** | ||
| 265 | * Tests if verbose output for the memory system is enabled. | ||
| 266 | * | ||
| 267 | * @return <tt>true</tt> if verbose output for the memory | ||
| 268 | * system is enabled; <tt>false</tt> otherwise. | ||
| 269 | */ | ||
| 270 | public boolean isVerbose(); | ||
| 271 | |||
| 272 | /** | ||
| 273 | * Enables or disables verbose output for the memory | ||
| 274 | * system. The verbose output information and the output stream | ||
| 275 | * to which the verbose information is emitted are implementation | ||
| 276 | * dependent. Typically, a Java virtual machine implementation | ||
| 277 | * prints a message whenever it frees memory at garbage collection. | ||
| 278 | * | ||
| 279 | * <p> | ||
| 280 | * Each invocation of this method enables or disables verbose | ||
| 281 | * output globally. | ||
| 282 | * | ||
| 283 | * @param value <tt>true</tt> to enable verbose output; | ||
| 284 | * <tt>false</tt> to disable. | ||
| 285 | * | ||
| 286 | * @exception java.lang.SecurityException if a security manager | ||
| 287 | * exists and the caller does not have | ||
| 288 | * ManagementPermission("control"). | ||
| 289 | */ | ||
| 290 | public void setVerbose(boolean value); | ||
| 291 | |||
| 292 | /** | ||
| 293 | * Runs the garbage collector. | ||
| 294 | * The call <code>gc()</code> is effectively equivalent to the | ||
| 295 | * call: | ||
| 296 | * <blockquote><pre> | ||
| 297 | * System.gc() | ||
| 298 | * </pre></blockquote> | ||
| 299 | * | ||
| 300 | * @see java.lang.System#gc() | ||
| 301 | */ | ||
| 302 | public void gc(); | ||
| 303 | |||
| 304 | } | ||