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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 | +} | |