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     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

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     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).

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    20  *

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    25 

    26 package java.lang.management;

    27 

    28 /**

    29  * The management interface for a memory pool.  A memory pool

    30  * represents the memory resource managed by the Java virtual machine

    31  * and is managed by one or more {@link MemoryManagerMXBean memory managers}.

    32  *

    33  * <p> A Java virtual machine has one or more instances of the

    34  * implementation class of this interface.  An instance

    35  * implementing this interface is

    36  * an <a href="ManagementFactory.html#MXBean">MXBean</a>

    37  * that can be obtained by calling

    38  * the {@link ManagementFactory#getMemoryPoolMXBeans} method or

    39  * from the {@link ManagementFactory#getPlatformMBeanServer

    40  * platform MBeanServer} method.

    41  *

    42  * <p>The {@code ObjectName} for uniquely identifying the MXBean for

    43  * a memory pool within an {@code MBeanServer} is:

    44  * <blockquote>

    45  *    {@link ManagementFactory#MEMORY_POOL_MXBEAN_DOMAIN_TYPE

    46  *    java.lang:type=MemoryPool}{@code ,name=}<i>pool's name</i>

    47  * </blockquote>

    48  *

    49  * It can be obtained by calling the

    50  * {@link PlatformManagedObject#getObjectName} method.

    51  *

    52  * <h3>Memory Type</h3>

    53  * <p>The Java virtual machine has a heap for object allocation and also

    54  * maintains non-heap memory for the method area and the Java virtual

    55  * machine execution.  The Java virtual machine can have one or more

    56  * memory pools.  Each memory pool represents a memory area

    57  * of one of the following types:

    58  * <ul>

    59  *   <li>{@link MemoryType#HEAP heap}</li>

    60  *   <li>{@link MemoryType#NON_HEAP non-heap}</li>

    61  * </ul>

    62  *

    63  * <h3>Memory Usage Monitoring</h3>

    64  *

    65  * A memory pool has the following attributes:

    66  * <ul>

    67  *   <li><a href="#Usage">Memory usage</a></li>

    68  *   <li><a href="#PeakUsage">Peak memory usage</a></li>

    69  *   <li><a href="#UsageThreshold">Usage Threshold</a></li>

    70  *   <li><a href="#CollectionThreshold">Collection Usage Threshold</a>

    71  *       (only supported by some <em>garbage-collected</em> memory pools)</li>

    72  * </ul>

    73  *

    74  * <h3><a id="Usage">1. Memory Usage</a></h3>

    75  *

    76  * The {@link #getUsage} method provides an estimate

    77  * of the current usage of a memory pool.

    78  * For a garbage-collected memory pool, the amount of used memory

    79  * includes the memory occupied by all objects in the pool

    80  * including both <em>reachable</em> and <em>unreachable</em> objects.

    81  *

    82  * <p>In general, this method is a lightweight operation for getting

    83  * an approximate memory usage.  For some memory pools, for example,

    84  * when objects are not packed contiguously, this method may be

    85  * an expensive operation that requires some computation to determine

    86  * the current memory usage.  An implementation should document when

    87  * this is the case.

    88  *

    89  * <h3><a id="PeakUsage">2. Peak Memory Usage</a></h3>

    90  *

    91  * The Java virtual machine maintains the peak memory usage of a memory

    92  * pool since the virtual machine was started or the peak was reset.

    93  * The peak memory usage is returned by the {@link #getPeakUsage} method

    94  * and reset by calling the {@link #resetPeakUsage} method.

    95  *

    96  * <h3><a id="UsageThreshold">3. Usage Threshold</a></h3>

    97  *

    98  * Each memory pool has a manageable attribute

    99  * called the <i>usage threshold</i> which has a default value supplied

   100  * by the Java virtual machine.  The default value is platform-dependent.

   101  * The usage threshold can be set via the

   102  * {@link #setUsageThreshold setUsageThreshold} method.

   103  * If the threshold is set to a positive value, the usage threshold crossing

   104  * checking is enabled in this memory pool.

   105  * If the usage threshold is set to zero, usage

   106  * threshold crossing checking on this memory pool is disabled.

   107  * The {@link MemoryPoolMXBean#isUsageThresholdSupported} method can

   108  * be used to determine if this functionality is supported.

   109  * <p>

   110  * A Java virtual machine performs usage threshold crossing checking on a

   111  * memory pool basis at its best appropriate time, typically,

   112  * at garbage collection time.

   113  * Each memory pool maintains a {@link #getUsageThresholdCount

   114  * usage threshold count} that will get incremented

   115  * every time when the Java virtual machine

   116  * detects that the memory pool usage is crossing the threshold.

   117  * <p>

   118  * This manageable usage threshold attribute is designed for monitoring the

   119  * increasing trend of memory usage with low overhead.

   120  * Usage threshold may not be appropriate for some memory pools.

   121  * For example, a generational garbage collector, a common garbage collection

   122  * algorithm used in many Java virtual machine implementations,

   123  * manages two or more generations segregating objects by age.

   124  * Most of the objects are allocated in

   125  * the <em>youngest generation</em> (say a nursery memory pool).

   126  * The nursery memory pool is designed to be filled up and

   127  * collecting the nursery memory pool will free most of its memory space

   128  * since it is expected to contain mostly short-lived objects

   129  * and mostly are unreachable at garbage collection time.

   130  * In this case, it is more appropriate for the nursery memory pool

   131  * not to support a usage threshold.  In addition,

   132  * if the cost of an object allocation

   133  * in one memory pool is very low (for example, just atomic pointer exchange),

   134  * the Java virtual machine would probably not support the usage threshold

   135  * for that memory pool since the overhead in comparing the usage with

   136  * the threshold is higher than the cost of object allocation.

   137  *

   138  * <p>

   139  * The memory usage of the system can be monitored using

   140  * <a href="#Polling">polling</a> or

   141  * <a href="#ThresholdNotification">threshold notification</a> mechanisms.

   142  *

   143  * <ol type="a">

   144  *   <li><a id="Polling"><b>Polling</b></a>

   145  *       <p>

   146  *       An application can continuously monitor its memory usage

   147  *       by calling either the {@link #getUsage} method for all

   148  *       memory pools or the {@link #isUsageThresholdExceeded} method

   149  *       for those memory pools that support a usage threshold.

   150  *       Below is example code that has a thread dedicated for

   151  *       task distribution and processing.  At every interval,

   152  *       it will determine if it should receive and process new tasks based

   153  *       on its memory usage.  If the memory usage exceeds its usage threshold,

   154  *       it will redistribute all outstanding tasks to other VMs and

   155  *       stop receiving new tasks until the memory usage returns

   156  *       below its usage threshold.

   157  *

   158  *       <pre>

   159  *       // Assume the usage threshold is supported for this pool.

   160  *       // Set the threshold to myThreshold above which no new tasks

   161  *       // should be taken.

   162  *       pool.setUsageThreshold(myThreshold);

   163  *       ....

   164  *

   165  *       boolean lowMemory = false;

   166  *       while (true) {

   167  *          if (pool.isUsageThresholdExceeded()) {

   168  *              // potential low memory, so redistribute tasks to other VMs

   169  *              lowMemory = true;

   170  *              redistributeTasks();

   171  *              // stop receiving new tasks

   172  *              stopReceivingTasks();

   173  *          } else {

   174  *              if (lowMemory) {

   175  *                  // resume receiving tasks

   176  *                  lowMemory = false;

   177  *                  resumeReceivingTasks();

   178  *              }

   179  *              // processing outstanding task

   180  *              ...

   181  *          }

   182  *          // sleep for sometime

   183  *          try {

   184  *              Thread.sleep(sometime);

   185  *          } catch (InterruptedException e) {

   186  *              ...

   187  *          }

   188  *       }

   189  *       </pre>

   190  *

   191  * <hr>

   192  *       The above example does not differentiate the case where

   193  *       the memory usage has temporarily dropped below the usage threshold

   194  *       from the case where the memory usage remains above the threshold

   195  *       between two iterations.  The usage threshold count returned by

   196  *       the {@link #getUsageThresholdCount} method

   197  *       can be used to determine

   198  *       if the memory usage has returned below the threshold

   199  *       between two polls.

   200  *       <p>

   201  *       Below shows another example that takes some action if a

   202  *       memory pool is under low memory and ignores the memory usage

   203  *       changes during the action processing time.

   204  *

   205  *       <pre>

   206  *       // Assume the usage threshold is supported for this pool.

   207  *       // Set the threshold to myThreshold which determines if

   208  *       // the application will take some action under low memory condition.

   209  *       pool.setUsageThreshold(myThreshold);

   210  *

   211  *       int prevCrossingCount = 0;

   212  *       while (true) {

   213  *           // A busy loop to detect when the memory usage

   214  *           // has exceeded the threshold.

   215  *           while (!pool.isUsageThresholdExceeded() ||

   216  *                  pool.getUsageThresholdCount() == prevCrossingCount) {

   217  *               try {

   218  *                   Thread.sleep(sometime)

   219  *               } catch (InterruptException e) {

   220  *                   ....

   221  *               }

   222  *           }

   223  *

   224  *           // Do some processing such as check for memory usage

   225  *           // and issue a warning

   226  *           ....

   227  *

   228  *           // Gets the current threshold count. The busy loop will then

   229  *           // ignore any crossing of threshold happens during the processing.

   230  *           prevCrossingCount = pool.getUsageThresholdCount();

   231  *       }

   232  *       </pre><hr>

   233  *   </li>

   234  *   <li><a id="ThresholdNotification"><b>Usage Threshold Notifications</b></a>

   235  *       <p>

   236  *       Usage threshold notification will be emitted by {@link MemoryMXBean}.

   237  *       When the Java virtual machine detects that the memory usage of

   238  *       a memory pool has reached or exceeded the usage threshold

   239  *       the virtual machine will trigger the {@code MemoryMXBean} to emit an

   240  *       {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED

   241  *       usage threshold exceeded notification}.

   242  *       Another usage threshold exceeded notification will not be

   243  *       generated until the usage has fallen below the threshold and

   244  *       then exceeded it again.

   245  *       <p>

   246  *       Below is an example code implementing the same logic as the

   247  *       first example above but using the usage threshold notification

   248  *       mechanism to detect low memory conditions instead of polling.

   249  *       In this example code, upon receiving notification, the notification

   250  *       listener notifies another thread to perform the actual action

   251  *       such as to redistribute outstanding tasks, stop receiving tasks,

   252  *       or resume receiving tasks.

   253  *       The {@code handleNotification} method should be designed to

   254  *       do a very minimal amount of work and return without delay to avoid

   255  *       causing delay in delivering subsequent notifications.  Time-consuming

   256  *       actions should be performed by a separate thread.

   257  *       The notification listener may be invoked by multiple threads

   258  *       concurrently; so the tasks performed by the listener

   259  *       should be properly synchronized.

   260  *

   261  *       <pre>

   262  *       class MyListener implements javax.management.NotificationListener {

   263  *            public void handleNotification(Notification notification, Object handback)  {

   264  *                String notifType = notification.getType();

   265  *                if (notifType.equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {

   266  *                    // potential low memory, notify another thread

   267  *                    // to redistribute outstanding tasks to other VMs

   268  *                    // and stop receiving new tasks.

   269  *                    lowMemory = true;

   270  *                    notifyAnotherThread(lowMemory);

   271  *                }

   272  *            }

   273  *       }

   274  *

   275  *       // Register MyListener with MemoryMXBean

   276  *       MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();

   277  *       NotificationEmitter emitter = (NotificationEmitter) mbean;

   278  *       MyListener listener = new MyListener();

   279  *       emitter.addNotificationListener(listener, null, null);

   280  *

   281  *       // Assume this pool supports a usage threshold.

   282  *       // Set the threshold to myThreshold above which no new tasks

   283  *       // should be taken.

   284  *       pool.setUsageThreshold(myThreshold);

   285  *

   286  *       // Usage threshold detection is enabled and notification will be

   287  *       // handled by MyListener.  Continue for other processing.

   288  *       ....

   289  *

   290  *       </pre>

   291  * <hr>

   292  *       <p>

   293  *       There is no guarantee about when the {@code MemoryMXBean} will emit

   294  *       a threshold notification and when the notification will be delivered.

   295  *       When a notification listener is invoked, the memory usage of

   296  *       the memory pool may have crossed the usage threshold more

   297  *       than once.

   298  *       The {@link MemoryNotificationInfo#getCount} method returns the number

   299  *       of times that the memory usage has crossed the usage threshold

   300  *       at the point in time when the notification was constructed.

   301  *       It can be compared with the current usage threshold count returned

   302  *       by the {@link #getUsageThresholdCount} method to determine if

   303  *       such situation has occurred.

   304  *   </li>

   305  * </ol>

   306  *

   307  * <h3><a id="CollectionThreshold">4. Collection Usage Threshold</a></h3>

   308  *

   309  * Collection usage threshold is a manageable attribute only applicable

   310  * to some garbage-collected memory pools.

   311  * After a Java virtual machine has expended effort in reclaiming memory

   312  * space by recycling unused objects in a memory pool at garbage collection

   313  * time, some number of bytes in the memory pools that are garbaged

   314  * collected will still be in use.  The collection usage threshold

   315  * allows a value to be set for this number of bytes such

   316  * that if the threshold is exceeded,

   317  * a {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED

   318  * collection usage threshold exceeded notification}

   319  * will be emitted by the {@link MemoryMXBean}.

   320  * In addition, the {@link #getCollectionUsageThresholdCount

   321  * collection usage threshold count} will then be incremented.

   322  *

   323  * <p>

   324  * The {@link MemoryPoolMXBean#isCollectionUsageThresholdSupported} method can

   325  * be used to determine if this functionality is supported.

   326  *

   327  * <p>

   328  * A Java virtual machine performs collection usage threshold checking

   329  * on a memory pool basis.  This checking is enabled if the collection

   330  * usage threshold is set to a positive value.

   331  * If the collection usage threshold is set to zero, this checking

   332  * is disabled on this memory pool.  Default value is zero.

   333  * The Java virtual machine performs the collection usage threshold

   334  * checking at garbage collection time.

   335  *

   336  * <p>

   337  * Some garbage-collected memory pools may

   338  * choose not to support the collection usage threshold.  For example,

   339  * a memory pool is only managed by a continuous concurrent garbage

   340  * collector.  Objects can be allocated in this memory pool by some thread

   341  * while the unused objects are reclaimed by the concurrent garbage

   342  * collector simultaneously.  Unless there is a well-defined

   343  * garbage collection time which is the best appropriate time

   344  * to check the memory usage, the collection usage threshold should not

   345  * be supported.

   346  *

   347  * <p>

   348  * The collection usage threshold is designed for monitoring the memory usage

   349  * after the Java virtual machine has expended effort in reclaiming

   350  * memory space.  The collection usage could also be monitored

   351  * by the polling and threshold notification mechanism

   352  * described above for the <a href="#UsageThreshold">usage threshold</a>

   353  * in a similar fashion.

   354  *

   355  * @see ManagementFactory#getPlatformMXBeans(Class)

   356  * @see <a href="../../../javax/management/package-summary.html">

   357  *      JMX Specification.</a>

   358  * @see <a href="package-summary.html#examples">

   359  *      Ways to Access MXBeans</a>

   360  *

   361  * @author  Mandy Chung

   362  * @since   1.5

   363  */

   364 public interface MemoryPoolMXBean extends PlatformManagedObject {

   365     /**

   366      * Returns the name representing this memory pool.

   367      *

   368      * @return the name of this memory pool.

   369      */

   370     public String getName();

   371 

   372     /**

   373      * Returns the type of this memory pool.

   374      *

   375      * <p>

   376      * <b>MBeanServer access</b>:<br>

   377      * The mapped type of {@code MemoryType} is {@code String}

   378      * and the value is the name of the {@code MemoryType}.

   379      *

   380      * @return the type of this memory pool.

   381      */

   382     public MemoryType getType();

   383 

   384     /**

   385      * Returns an estimate of the memory usage of this memory pool.

   386      * This method returns {@code null}

   387      * if this memory pool is not valid (i.e. no longer exists).

   388      *

   389      * <p>

   390      * This method requests the Java virtual machine to make

   391      * a best-effort estimate of the current memory usage of this

   392      * memory pool. For some memory pools, this method may be an

   393      * expensive operation that requires some computation to determine

   394      * the estimate.  An implementation should document when

   395      * this is the case.

   396      *

   397      * <p>This method is designed for use in monitoring system

   398      * memory usage and detecting low memory condition.

   399      *

   400      * <p>

   401      * <b>MBeanServer access</b>:<br>

   402      * The mapped type of {@code MemoryUsage} is

   403      * {@code CompositeData} with attributes as specified in

   404      * {@link MemoryUsage#from MemoryUsage}.

   405      *

   406      * @return a {@link MemoryUsage} object; or {@code null} if

   407      * this pool not valid.

   408      */

   409     public MemoryUsage getUsage();

   410 

   411     /**

   412      * Returns the peak memory usage of this memory pool since the

   413      * Java virtual machine was started or since the peak was reset.

   414      * This method returns {@code null}

   415      * if this memory pool is not valid (i.e. no longer exists).

   416      *

   417      * <p>

   418      * <b>MBeanServer access</b>:<br>

   419      * The mapped type of {@code MemoryUsage} is

   420      * {@code CompositeData} with attributes as specified in

   421      * {@link MemoryUsage#from MemoryUsage}.

   422      *

   423      * @return a {@link MemoryUsage} object representing the peak

   424      * memory usage; or {@code null} if this pool is not valid.

   425      *

   426      */

   427     public MemoryUsage getPeakUsage();

   428 

   429     /**

   430      * Resets the peak memory usage statistic of this memory pool

   431      * to the current memory usage.

   432      *

   433      * @throws java.lang.SecurityException if a security manager

   434      *         exists and the caller does not have

   435      *         ManagementPermission("control").

   436      */

   437     public void resetPeakUsage();

   438 

   439     /**

   440      * Tests if this memory pool is valid in the Java virtual

   441      * machine.  A memory pool becomes invalid once the Java virtual

   442      * machine removes it from the memory system.

   443      *

   444      * @return {@code true} if the memory pool is valid in the running

   445      *              Java virtual machine;

   446      *         {@code false} otherwise.

   447      */

   448     public boolean isValid();

   449 

   450     /**

   451      * Returns the name of memory managers that manages this memory pool.

   452      * Each memory pool will be managed by at least one memory manager.

   453      *

   454      * @return an array of {@code String} objects, each is the name of

   455      * a memory manager managing this memory pool.

   456      */

   457     public String[] getMemoryManagerNames();

   458 

   459     /**

   460      * Returns the usage threshold value of this memory pool in bytes.

   461      * Each memory pool has a platform-dependent default threshold value.

   462      * The current usage threshold can be changed via the

   463      * {@link #setUsageThreshold setUsageThreshold} method.

   464      *

   465      * @return the usage threshold value of this memory pool in bytes.

   466      *

   467      * @throws UnsupportedOperationException if this memory pool

   468      *         does not support a usage threshold.

   469      *

   470      * @see #isUsageThresholdSupported

   471      */

   472     public long getUsageThreshold();

   473 

   474     /**

   475      * Sets the threshold of this memory pool to the given {@code threshold}

   476      * value if this memory pool supports the usage threshold.

   477      * The usage threshold crossing checking is enabled in this memory pool

   478      * if the threshold is set to a positive value.

   479      * The usage threshold crossing checking is disabled

   480      * if it is set to zero.

   481      *

   482      * @param threshold the new threshold value in bytes. Must be non-negative.

   483      *

   484      * @throws IllegalArgumentException if {@code threshold} is negative

   485      *         or greater than the maximum amount of memory for

   486      *         this memory pool if defined.

   487      *

   488      * @throws UnsupportedOperationException if this memory pool

   489      *         does not support a usage threshold.

   490      *

   491      * @throws java.lang.SecurityException if a security manager

   492      *         exists and the caller does not have

   493      *         ManagementPermission("control").

   494      *

   495      * @see #isUsageThresholdSupported

   496      * @see <a href="#UsageThreshold">Usage threshold</a>

   497      */

   498     public void setUsageThreshold(long threshold);

   499 

   500     /**

   501      * Tests if the memory usage of this memory pool

   502      * reaches or exceeds its usage threshold value.

   503      *

   504      * @return {@code true} if the memory usage of

   505      * this memory pool reaches or exceeds the threshold value;

   506      * {@code false} otherwise.

   507      *

   508      * @throws UnsupportedOperationException if this memory pool

   509      *         does not support a usage threshold.

   510      */

   511     public boolean isUsageThresholdExceeded();

   512 

   513     /**

   514      * Returns the number of times that the memory usage has crossed

   515      * the usage threshold.

   516      *

   517      * @return the number of times that the memory usage

   518      * has crossed its usage threshold value.

   519      *

   520      * @throws UnsupportedOperationException if this memory pool

   521      * does not support a usage threshold.

   522      */

   523     public long getUsageThresholdCount();

   524 

   525     /**

   526      * Tests if this memory pool supports usage threshold.

   527      *

   528      * @return {@code true} if this memory pool supports usage threshold;

   529      * {@code false} otherwise.

   530      */

   531     public boolean isUsageThresholdSupported();

   532 

   533     /**

   534      * Returns the collection usage threshold value of this memory pool

   535      * in bytes.  The default value is zero. The collection usage

   536      * threshold can be changed via the

   537      * {@link #setCollectionUsageThreshold setCollectionUsageThreshold} method.

   538      *

   539      * @return the collection usage threshold of this memory pool in bytes.

   540      *

   541      * @throws UnsupportedOperationException if this memory pool

   542      *         does not support a collection usage threshold.

   543      *

   544      * @see #isCollectionUsageThresholdSupported

   545      */

   546     public long getCollectionUsageThreshold();

   547 

   548     /**

   549      * Sets the collection usage threshold of this memory pool to

   550      * the given {@code threshold} value.

   551      * When this threshold is set to positive, the Java virtual machine

   552      * will check the memory usage at its best appropriate time after it has

   553      * expended effort in recycling unused objects in this memory pool.

   554      * <p>

   555      * The collection usage threshold crossing checking is enabled

   556      * in this memory pool if the threshold is set to a positive value.

   557      * The collection usage threshold crossing checking is disabled

   558      * if it is set to zero.

   559      *

   560      * @param threshold the new collection usage threshold value in bytes.

   561      *              Must be non-negative.

   562      *

   563      * @throws IllegalArgumentException if {@code threshold} is negative

   564      *         or greater than the maximum amount of memory for

   565      *         this memory pool if defined.

   566      *

   567      * @throws UnsupportedOperationException if this memory pool

   568      *         does not support a collection usage threshold.

   569      *

   570      * @throws java.lang.SecurityException if a security manager

   571      *         exists and the caller does not have

   572      *         ManagementPermission("control").

   573      *

   574      * @see #isCollectionUsageThresholdSupported

   575      * @see <a href="#CollectionThreshold">Collection usage threshold</a>

   576      */

   577     public void setCollectionUsageThreshold(long threshold);

   578 

   579     /**

   580      * Tests if the memory usage of this memory pool after

   581      * the most recent collection on which the Java virtual

   582      * machine has expended effort has reached or

   583      * exceeded its collection usage threshold.

   584      * This method does not request the Java virtual

   585      * machine to perform any garbage collection other than its normal

   586      * automatic memory management.

   587      *

   588      * @return {@code true} if the memory usage of this memory pool

   589      * reaches or exceeds the collection usage threshold value

   590      * in the most recent collection;

   591      * {@code false} otherwise.

   592      *

   593      * @throws UnsupportedOperationException if this memory pool

   594      *         does not support a usage threshold.

   595      */

   596     public boolean isCollectionUsageThresholdExceeded();

   597 

   598     /**

   599      * Returns the number of times that the Java virtual machine

   600      * has detected that the memory usage has reached or

   601      * exceeded the collection usage threshold.

   602      *

   603      * @return the number of times that the memory

   604      * usage has reached or exceeded the collection usage threshold.

   605      *

   606      * @throws UnsupportedOperationException if this memory pool

   607      *         does not support a collection usage threshold.

   608      *

   609      * @see #isCollectionUsageThresholdSupported

   610      */

   611     public long getCollectionUsageThresholdCount();

   612 

   613     /**

   614      * Returns the memory usage after the Java virtual machine

   615      * most recently expended effort in recycling unused objects

   616      * in this memory pool.

   617      * This method does not request the Java virtual

   618      * machine to perform any garbage collection other than its normal

   619      * automatic memory management.

   620      * This method returns {@code null} if the Java virtual

   621      * machine does not support this method.

   622      *

   623      * <p>

   624      * <b>MBeanServer access</b>:<br>

   625      * The mapped type of {@code MemoryUsage} is

   626      * {@code CompositeData} with attributes as specified in

   627      * {@link MemoryUsage#from MemoryUsage}.

   628      *

   629      * @return a {@link MemoryUsage} representing the memory usage of

   630      * this memory pool after the Java virtual machine most recently

   631      * expended effort in recycling unused objects;

   632      * {@code null} if this method is not supported.

   633      */

   634     public MemoryUsage getCollectionUsage();

   635 

   636     /**

   637      * Tests if this memory pool supports a collection usage threshold.

   638      *

   639      * @return {@code true} if this memory pool supports the

   640      * collection usage threshold; {@code false} otherwise.

   641      */

   642     public boolean isCollectionUsageThresholdSupported();

   643 }