- /*
- * @(#)MemoryPoolMXBean.java 1.18 04/04/20
- *
- * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
- * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- */
-
- package java.lang.management;
-
- /**
- * The management interface for a memory pool. A memory pool
- * represents the memory resource managed by the Java virtual machine
- * and is managed by one or more {@link MemoryManagerMXBean memory managers}.
- *
- * <p> A Java virtual machine has one or more instances of the
- * implementation class of this interface. An instance
- * implementing this interface is
- * an <a href="ManagementFactory.html#MXBean">MXBean</a>
- * that can be obtained by calling
- * the {@link ManagementFactory#getMemoryPoolMXBeans} method or
- * from the {@link ManagementFactory#getPlatformMBeanServer
- * platform <tt>MBeanServer</tt>} method.
- *
- * <p>The <tt>ObjectName</tt> for uniquely identifying the MXBean for
- * a memory pool within an <tt>MBeanServer</tt> is:
- * <blockquote>
- * {@link ManagementFactory#MEMORY_POOL_MXBEAN_DOMAIN_TYPE
- * <tt>java.lang:type=MemoryPool</tt>}<tt>,name=</tt><i>pool's name</i>
- * </blockquote>
- *
- * <h4>Memory Type</h4>
- * <p>The Java virtual machine has a heap for object allocation and also
- * maintains non-heap memory for the method area and the Java virtual
- * machine execution. The Java virtual machine can have one or more
- * memory pools. Each memory pool represents a memory area
- * of one of the following types:
- * <ul>
- * <li>{@link MemoryType#HEAP heap}</li>
- * <li>{@link MemoryType#NON_HEAP non-heap}</li>
- * </ul>
- *
- * <h4>Memory Usage Monitoring</h4>
- *
- * A memory pool has the following attributes:
- * <ul>
- * <li><a href="Usage">Memory usage</a></li>
- * <li><a href="PeakUsage">Peak memory usage</a></li>
- * <li><a href="UsageThreshold">Usage Threshold</a></li>
- * <li><a href="CollectionThreshold">Collection Usage Threshold</a>
- * (only supported by some <em>garbage-collected</em> memory pools)</li>
- * </ul>
- *
- * <h4><a name="Usage">1. Memory Usage</a></h4>
- *
- * The {@link #getUsage} method provides an estimate
- * of the current usage of a memory pool.
- * For a garbage-collected memory pool, the amount of used memory
- * includes the memory occupied by all objects in the pool
- * including both <em>reachable</em> and <em>unreachable</em> objects.
- *
- * <p>In general, this method is a lightweight operation for getting
- * an approximate memory usage. For some memory pools, for example,
- * when objects are not packed contiguously, this method may be
- * an expensive operation that requires some computation to determine
- * the current memory usage. An implementation should document when
- * this is the case.
- *
- * <h4><a name="PeakUsage">2. Peak Memory Usage</a></h4>
- *
- * The Java virtual machine maintains the peak memory usage of a memory
- * pool since the virtual machine was started or the peak was reset.
- * The peak memory usage is returned by the {@link #getPeakUsage} method
- * and reset by calling the {@link #resetPeakUsage} method.
- *
- * <h4><a name="UsageThreshold">3. Usage Threshold</a></h4>
- *
- * Each memory pool has a manageable attribute
- * called the <i>usage threshold</i> which has a default value supplied
- * by the Java virtual machine. The default value is platform-dependent.
- * The usage threshold can be set via the
- * {@link #setUsageThreshold setUsageThreshold} method.
- * If the threshold is set to a positive value, the usage threshold crossing
- * checking is enabled in this memory pool.
- * If the usage threshold is set to zero, usage
- * threshold crossing checking on this memory pool is disabled.
- * The {@link MemoryPoolMXBean#isUsageThresholdSupported} method can
- * be used to determine if this functionality is supported.
- * <p>
- * A Java virtual machine performs usage threshold crossing checking on a
- * memory pool basis at its best appropriate time, typically,
- * at garbage collection time.
- * Each memory pool maintains a {@link #getUsageThresholdCount
- * usage threshold count} that will get incremented
- * every time when the Java virtual machine
- * detects that the memory pool usage is crossing the threshold.
- * <p>
- * This manageable usage threshold attribute is designed for monitoring the
- * increasing trend of memory usage with low overhead.
- * Usage threshold may not be appropriate for some memory pools.
- * For example, a generational garbage collector, a common garbage collection
- * algorithm used in many Java virtual machine implementations,
- * manages two or more generations segregating objects by age.
- * Most of the objects are allocated in
- * the <em>youngest generation</em> (say a nursery memory pool).
- * The nursery memory pool is designed to be filled up and
- * collecting the nursery memory pool will free most of its memory space
- * since it is expected to contain mostly short-lived objects
- * and mostly are unreachable at garbage collection time.
- * In this case, it is more appropriate for the nursery memory pool
- * not to support a usage threshold. In addition,
- * if the cost of an object allocation
- * in one memory pool is very low (for example, just atomic pointer exchange),
- * the Java virtual machine would probably not support the usage threshold
- * for that memory pool since the overhead in comparing the usage with
- * the threshold is higher than the cost of object allocation.
- *
- * <p>
- * The memory usage of the system can be monitored using
- * <a href="#Polling">polling</a> or
- * <a href="#Notification">threshold notification</a> mechanisms.
- *
- * <ol type="a">
- * <li><a name="Polling"><b>Polling</b></a>
- * <p>
- * An application can continuously monitor its memory usage
- * by calling either the {@link #getUsage} method for all
- * memory pools or the {@link #isUsageThresholdExceeded} method
- * for those memory pools that support a usage threshold.
- * Below is example code that has a thread delicated for
- * task distribution and processing. At every interval,
- * it will determine if it should receive and process new tasks based
- * on its memory usage. If the memory usage exceeds its usage threshold,
- * it will redistribute all outstanding tasks to other VMs and
- * stop receiving new tasks until the memory usage returns
- * below its usage threshold.
- *
- * <pre>
- * // Assume the usage threshold is supported for this pool.
- * // Set the threshold to myThreshold above which no new tasks
- * // should be taken.
- * pool.setUsageThreshold(myThreshold);
- * ....
- *
- * boolean lowMemory = false;
- * while (true) {
- * if (pool.isUsageThresholdExceeded()) {
- * // potential low memory, so redistribute tasks to other VMs
- * lowMemory = true;
- * redistributeTasks();
- * // stop receiving new tasks
- * stopReceivingTasks();
- * } else {
- * if (lowMemory) {
- * // resume receiving tasks
- * lowMemory = false;
- * resumeReceivingTasks();
- * }
- * // processing outstanding task
- * ...
- * }
- * // sleep for sometime
- * try {
- * Thread.sleep(sometime);
- * } catch (InterruptedException e) {
- * ...
- * }
- * }
- * </pre>
- *
- * <hr>
- * The above example does not differentiate the case where
- * the memory usage has temporarily dropped below the usage threshold
- * from the case where the memory usage remains above the threshould
- * between two iterations. The usage threshold count returned by
- * the {@link #getUsageThresholdCount} method
- * can be used to determine
- * if the memory usage has returned below the threshold
- * between two polls.
- * <p>
- * Below shows another example that takes some action if a
- * memory pool is under low memory and ignores the memory usage
- * changes during the action processing time.
- *
- * <pre>
- * // Assume the usage threshold is supported for this pool.
- * // Set the threshold to myThreshold which determines if
- * // the application will take some action under low memory condition.
- * pool.setUsageThreshold(myThreshold);
- *
- * int prevCrossingCount = 0;
- * while (true) {
- * // A busy loop to detect when the memory usage
- * // has exceeded the threshold.
- * while (!pool.isUsageThresholdExceeded() ||
- * pool.getUsageThresholdCount() == prevCrossingCount) {
- * try {
- * Thread.sleep(sometime)
- * } catch (InterruptException e) {
- * ....
- * }
- * }
- *
- * // Do some processing such as check for memory usage
- * // and issue a warning
- * ....
- *
- * // Gets the current threshold count. The busy loop will then
- * // ignore any crossing of threshold happens during the processing.
- * prevCrossingCount = pool.getUsageThresholdCount();
- * }
- * </pre><hr>
- * </li>
- * <li><a name="ThresholdNotification"><b>Usage Threshold Notifications</b></a>
- * <p>
- * Usage threshold notification will be emitted by {@link MemoryMXBean}.
- * When the Java virtual machine detects that the memory usage of
- * a memory pool has reached or exceeded the usage threshold
- * the virtual machine will trigger the <tt>MemoryMXBean</tt> to emit an
- * {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED
- * usage threshold exceeded notification}.
- * Another usage threshold exceeded notification will not be
- * generated until the usage has fallen below the threshold and
- * then exceeded it again.
- * <p>
- * Below is an example code implementing the same logic as the
- * first example above but using the usage threshold notification
- * mechanism to detect low memory conditions instead of polling.
- * In this example code, upon receiving notification, the notification
- * listener notifies another thread to perform the actual action
- * such as to redistribute outstanding tasks, stop receiving tasks,
- * or resume receiving tasks.
- * The <tt>handleNotification</tt> method should be designed to
- * do a very minimal amount of work and return without delay to avoid
- * causing delay in delivering subsequent notifications. Time-consuming
- * actions should be performed by a separate thread.
- * The notification listener may be invoked by multiple threads
- * concurrently; so the tasks performed by the listener
- * should be properly synchronized.
- *
- * <pre>
- * class MyListener implements javax.management.NotificationListener {
- * public void handleNotification(Notification notification, Object handback) {
- * String notifType = notification.getType();
- * if (notifType.equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {
- * // potential low memory, notify another thread
- * // to redistribute outstanding tasks to other VMs
- * // and stop receiving new tasks.
- * lowMemory = true;
- * notifyAnotherThread(lowMemory);
- * }
- * }
- * }
- *
- * // Register MyListener with MemoryMXBean
- * MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();
- * NotificationEmitter emitter = (NotificationEmitter) mbean;
- * MyListener listener = new MyListener();
- * emitter.addNotificationListener(listener, null, null);
- *
- * // Assume this pool supports a usage threshold.
- * // Set the threshold to myThreshold above which no new tasks
- * // should be taken.
- * pool.setUsageThreshold(myThreshold);
- *
- * // Usage threshold detection is enabled and notification will be
- * // handled by MyListener. Continue for other processing.
- * ....
- *
- * </pre>
- * <hr>
- * <p>
- * There is no guarantee about when the <tt>MemoryMXBean</tt> will emit
- * a threshold notification and when the notification will be delivered.
- * When a notification listener is invoked, the memory usage of
- * the memory pool may have crossed the usage threshold more
- * than once.
- * The {@link MemoryNotificationInfo#getCount} method returns the number
- * of times that the memory usage has crossed the usage threshold
- * at the point in time when the notification was constructed.
- * It can be compared with the current usage threshold count returned
- * by the {@link #getUsageThresholdCount} method to determine if
- * such situation has occurred.
- * </li>
- * </ol>
- *
- * <h4><a name="CollectionThreshold">4. Collection Usage Threshold</a></h4>
- *
- * Collection usage threshold is a manageable attribute only applicable
- * to some garbage-collected memory pools.
- * After a Java virtual machine has expended effort in reclaiming memory
- * space by recycling unused objects in a memory pool at garbage collection
- * time, some number of bytes in the memory pools that are garbaged
- * collected will still be in use. The collection usage threshold
- * allows a value to be set for this number of bytes such
- * that if the threshold is exceeded,
- * a {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED
- * collection usage threshold exceeded notification}
- * will be emitted by the {@link MemoryMXBean}.
- * In addition, the {@link #getCollectionUsageThresholdCount
- * collection usage threshold count} will then be incremented.
- *
- * <p>
- * The {@link MemoryPoolMXBean#isCollectionUsageThresholdSupported} method can
- * be used to determine if this functionality is supported.
- *
- * <p>
- * A Java virtual machine performs collection usage threshold checking
- * on a memory pool basis. This checking is enabled if the collection
- * usage threshold is set to a positive value.
- * If the collection usage threshold is set to zero, this checking
- * is disabled on this memory pool. Default value is zero.
- * The Java virtual machine performs the collection usage threshold
- * checking at garbage collection time.
- *
- * <p>
- * Some garbage-collected memory pools may
- * choose not to support the collection usage threshold. For example,
- * a memory pool is only managed by a continuous concurrent garbage
- * collector. Objects can be allocated in this memory pool by some thread
- * while the unused objects are reclaimed by the concurrent garbage
- * collector simultaneously. Unless there is a well-defined
- * garbage collection time which is the best appropriate time
- * to check the memory usage, the collection usage threshold should not
- * be supported.
- *
- * <p>
- * The collection usage threshold is designed for monitoring the memory usage
- * after the Java virtual machine has expended effort in reclaiming
- * memory space. The collection usage could also be monitored
- * by the polling and threshold notification mechanism
- * described above for the <a href="#UsageThreshold">usage threshold</a>
- * in a similar fashion.
- *
- * @see <a href="../../../javax/management/package-summary.html">
- * JMX Specification.</a>
- * @see <a href="package-summary.html#examples">
- * Ways to Access MXBeans</a>
- *
- * @author Mandy Chung
- * @version 1.18, 04/20/04
- * @since 1.5
- */
- public interface MemoryPoolMXBean {
- /**
- * Returns the name representing this memory pool.
- *
- * @return the name of this memory pool.
- */
- public String getName();
-
- /**
- * Returns the type of this memory pool.
- *
- * <p>
- * <b>MBeanServer access</b>:<br>
- * The mapped type of <tt>MemoryType</tt> is <tt>String</tt>
- * and the value is the name of the <tt>MemoryType</tt>.
- *
- * @return the type of this memory pool.
- */
- public MemoryType getType();
-
- /**
- * Returns an estimate of the memory usage of this memory pool.
- * This method returns <tt>null</tt>
- * if this memory pool is not valid (i.e. no longer exists).
- *
- * <p>
- * This method requests the Java virtual machine to make
- * a best-effort estimate of the current memory usage of this
- * memory pool. For some memory pools, this method may be an
- * expensive operation that requires some computation to determine
- * the estimate. An implementation should document when
- * this is the case.
- *
- * <p>This method is designed for use in monitoring system
- * memory usage and detecting low memory condition.
- *
- * <p>
- * <b>MBeanServer access</b>:<br>
- * The mapped type of <tt>MemoryUsage</tt> is
- * <tt>CompositeData</tt> with attributes as specified in
- * {@link MemoryUsage#from MemoryUsage}.
- *
- * @return a {@link MemoryUsage} object; or <tt>null</tt> if
- * this pool not valid.
- */
- public MemoryUsage getUsage();
-
- /**
- * Returns the peak memory usage of this memory pool since the
- * Java virtual machine was started or since the peak was reset.
- * This method returns <tt>null</tt>
- * if this memory pool is not valid (i.e. no longer exists).
- *
- * <p>
- * <b>MBeanServer access</b>:<br>
- * The mapped type of <tt>MemoryUsage</tt> is
- * <tt>CompositeData</tt> with attributes as specified in
- * {@link MemoryUsage#from MemoryUsage}.
- *
- * @return a {@link MemoryUsage} object representing the peak
- * memory usage; or <tt>null</tt> if this pool is not valid.
- *
- */
- public MemoryUsage getPeakUsage();
-
- /**
- * Resets the peak memory usage statistic of this memory pool
- * to the current memory usage.
- *
- * @throws java.lang.SecurityException if a security manager
- * exists and the caller does not have
- * ManagementPermission("control").
- */
- public void resetPeakUsage();
-
- /**
- * Tests if this memory pool is valid in the Java virtual
- * machine. A memory pool becomes invalid once the Java virtual
- * machine removes it from the memory system.
- *
- * @return <tt>true</tt> if the memory pool is valid in the running
- * Java virtual machine;
- * <tt>false</tt> otherwise.
- */
- public boolean isValid();
-
- /**
- * Returns the name of memory managers that manages this memory pool.
- * Each memory pool will be managed by at least one memory manager.
- *
- * @return an array of <tt>String</tt> objects, each is the name of
- * a memory manager managing this memory pool.
- */
- public String[] getMemoryManagerNames();
-
- /**
- * Returns the usage threshold value of this memory pool in bytes.
- * Each memory pool has a platform-dependent default threshold value.
- * The current usage threshold can be changed via the
- * {@link #setUsageThreshold setUsageThreshold} method.
- *
- * @return the usage threshold value of this memory pool in bytes.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a usage threshold.
- *
- * @see #isUsageThresholdSupported
- */
- public long getUsageThreshold();
-
- /**
- * Sets the threshold of this memory pool to the given <tt>threshold</tt>
- * value if this memory pool supports the usage threshold.
- * The usage threshold crossing checking is enabled in this memory pool
- * if the threshold is set to a positive value.
- * The usage threshold crossing checking is disabled
- * if it is set to zero.
- *
- * @param threshold the new threshold value in bytes. Must be non-negative.
- *
- * @throws IllegalArgumentException if <tt>threshold</tt> is negative
- * or greater than the maximum amount of memory for
- * this memory pool if defined.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a usage threshold.
- *
- * @throws java.lang.SecurityException if a security manager
- * exists and the caller does not have
- * ManagementPermission("control").
- *
- * @see #isUsageThresholdSupported
- * @see <a href="#UsageThreshold">Usage threshold</a>
- */
- public void setUsageThreshold(long threshold);
-
- /**
- * Tests if the memory usage of this memory pool
- * reaches or exceeds its usage threshold value.
- *
- * @return <tt>true</tt> if the memory usage of
- * this memory pool reaches or exceeds the threshold value;
- * <tt>false</tt> otherwise.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a usage threshold.
- */
- public boolean isUsageThresholdExceeded();
-
- /**
- * Returns the number of times that the memory usage has crossed
- * the usage threshold.
- *
- * @return the number of times that the memory usage
- * has crossed its usage threshold value.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a usage threshold.
- */
- public long getUsageThresholdCount();
-
- /**
- * Tests if this memory pool supports usage threshold.
- *
- * @return <tt>true</tt> if this memory pool supports usage threshold;
- * <tt>false</tt> otherwise.
- */
- public boolean isUsageThresholdSupported();
-
- /**
- * Returns the collection usage threshold value of this memory pool
- * in bytes. The default value is zero. The collection usage
- * threshold can be changed via the
- * {@link #setCollectionUsageThreshold setCollectionUsageThreshold} method.
- *
- * @return the collection usage threshold of this memory pool in bytes.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a collection usage threshold.
- *
- * @see #isCollectionUsageThresholdSupported
- */
- public long getCollectionUsageThreshold();
-
- /**
- * Sets the collection usage threshold of this memory pool to
- * the given <tt>threshold</tt> value.
- * When this threshold is set to positive, the Java virtual machine
- * will check the memory usage at its best appropriate time after it has
- * expended effort in recycling unused objects in this memory pool.
- * <p>
- * The collection usage threshold crossing checking is enabled
- * in this memory pool if the threshold is set to a positive value.
- * The collection usage threshold crossing checking is disabled
- * if it is set to zero.
- *
- * @param threhsold the new collection usage threshold value in bytes.
- * Must be non-negative.
- *
- * @throws IllegalArgumentException if <tt>threshold</tt> is negative
- * or greater than the maximum amount of memory for
- * this memory pool if defined.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a collection usage threshold.
- *
- * @throws java.lang.SecurityException if a security manager
- * exists and the caller does not have
- * ManagementPermission("control").
- *
- * @see #isCollectionUsageThresholdSupported
- * @see <a href="#CollectionThreshold">Collection usage threshold</a>
- */
- public void setCollectionUsageThreshold(long threhsold);
-
- /**
- * Tests if the memory usage of this memory pool after
- * the most recent collection on which the Java virtual
- * machine has expended effort has reached or
- * exceeded its collection usage threshold.
- * This method does not request the Java virtual
- * machine to perform any garbage collection other than its normal
- * automatic memory management.
- *
- * @return <tt>true</tt> if the memory usage of this memory pool
- * reaches or exceeds the collection usage threshold value
- * in the most recent collection;
- * <tt>false</tt> otherwise.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a usage threshold.
- */
- public boolean isCollectionUsageThresholdExceeded();
-
- /**
- * Returns the number of times that the Java virtual machine
- * has detected that the memory usage has reached or
- * exceeded the collection usage threshold.
- *
- * @return the number of times that the memory
- * usage has reached or exceeded the collection usage threshold.
- *
- * @throws UnsupportedOperationException if this memory pool
- * does not support a collection usage threshold.
- *
- * @see #isCollectionUsageThresholdSupported
- */
- public long getCollectionUsageThresholdCount();
-
- /**
- * Returns the memory usage after the Java virtual machine
- * most recently expended effort in recycling unused objects
- * in this memory pool.
- * This method does not request the Java virtual
- * machine to perform any garbage collection other than its normal
- * automatic memory management.
- * This method returns <tt>null</tt> if the Java virtual
- * machine does not support this method.
- *
- * <p>
- * <b>MBeanServer access</b>:<br>
- * The mapped type of <tt>MemoryUsage</tt> is
- * <tt>CompositeData</tt> with attributes as specified in
- * {@link MemoryUsage#from MemoryUsage}.
- *
- * @return a {@link MemoryUsage} representing the memory usage of
- * this memory pool after the Java virtual machine most recently
- * expended effort in recycling unused objects;
- * <tt>null</tt> if this method is not supported.
- */
- public MemoryUsage getCollectionUsage();
-
- /**
- * Tests if this memory pool supports a collection usage threshold.
- *
- * @return <tt>true</tt> if this memory pool supports the
- * collection usage threshold; <tt>false</tt> otherwise.
- */
- public boolean isCollectionUsageThresholdSupported();
- }