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644 lines
26 KiB
644 lines
26 KiB
/*
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* Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*/
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package java.lang.management;
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/**
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* The management interface for a memory pool. A memory pool
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* represents the memory resource managed by the Java virtual machine
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* and is managed by one or more {@link MemoryManagerMXBean memory managers}.
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*
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* <p> A Java virtual machine has one or more instances of the
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* implementation class of this interface. An instance
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* implementing this interface is
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* an <a href="ManagementFactory.html#MXBean">MXBean</a>
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* that can be obtained by calling
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* the {@link ManagementFactory#getMemoryPoolMXBeans} method or
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* from the {@link ManagementFactory#getPlatformMBeanServer
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* platform <tt>MBeanServer</tt>} method.
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*
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* <p>The <tt>ObjectName</tt> for uniquely identifying the MXBean for
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* a memory pool within an <tt>MBeanServer</tt> is:
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* <blockquote>
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* {@link ManagementFactory#MEMORY_POOL_MXBEAN_DOMAIN_TYPE
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* <tt>java.lang:type=MemoryPool</tt>}<tt>,name=</tt><i>pool's name</i>
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* </blockquote>
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*
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* It can be obtained by calling the
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* {@link PlatformManagedObject#getObjectName} method.
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*
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* <h3>Memory Type</h3>
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* <p>The Java virtual machine has a heap for object allocation and also
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* maintains non-heap memory for the method area and the Java virtual
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* machine execution. The Java virtual machine can have one or more
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* memory pools. Each memory pool represents a memory area
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* of one of the following types:
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* <ul>
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* <li>{@link MemoryType#HEAP heap}</li>
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* <li>{@link MemoryType#NON_HEAP non-heap}</li>
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* </ul>
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*
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* <h3>Memory Usage Monitoring</h3>
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*
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* A memory pool has the following attributes:
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* <ul>
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* <li><a href="#Usage">Memory usage</a></li>
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* <li><a href="#PeakUsage">Peak memory usage</a></li>
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* <li><a href="#UsageThreshold">Usage Threshold</a></li>
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* <li><a href="#CollectionThreshold">Collection Usage Threshold</a>
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* (only supported by some <em>garbage-collected</em> memory pools)</li>
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* </ul>
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*
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* <h3><a name="Usage">1. Memory Usage</a></h3>
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*
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* The {@link #getUsage} method provides an estimate
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* of the current usage of a memory pool.
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* For a garbage-collected memory pool, the amount of used memory
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* includes the memory occupied by all objects in the pool
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* including both <em>reachable</em> and <em>unreachable</em> objects.
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*
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* <p>In general, this method is a lightweight operation for getting
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* an approximate memory usage. For some memory pools, for example,
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* when objects are not packed contiguously, this method may be
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* an expensive operation that requires some computation to determine
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* the current memory usage. An implementation should document when
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* this is the case.
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*
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* <h3><a name="PeakUsage">2. Peak Memory Usage</a></h3>
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*
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* The Java virtual machine maintains the peak memory usage of a memory
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* pool since the virtual machine was started or the peak was reset.
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* The peak memory usage is returned by the {@link #getPeakUsage} method
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* and reset by calling the {@link #resetPeakUsage} method.
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*
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* <h3><a name="UsageThreshold">3. Usage Threshold</a></h3>
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*
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* Each memory pool has a manageable attribute
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* called the <i>usage threshold</i> which has a default value supplied
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* by the Java virtual machine. The default value is platform-dependent.
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* The usage threshold can be set via the
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* {@link #setUsageThreshold setUsageThreshold} method.
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* If the threshold is set to a positive value, the usage threshold crossing
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* checking is enabled in this memory pool.
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* If the usage threshold is set to zero, usage
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* threshold crossing checking on this memory pool is disabled.
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* The {@link MemoryPoolMXBean#isUsageThresholdSupported} method can
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* be used to determine if this functionality is supported.
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* <p>
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* A Java virtual machine performs usage threshold crossing checking on a
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* memory pool basis at its best appropriate time, typically,
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* at garbage collection time.
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* Each memory pool maintains a {@link #getUsageThresholdCount
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* usage threshold count} that will get incremented
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* every time when the Java virtual machine
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* detects that the memory pool usage is crossing the threshold.
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* <p>
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* This manageable usage threshold attribute is designed for monitoring the
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* increasing trend of memory usage with low overhead.
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* Usage threshold may not be appropriate for some memory pools.
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* For example, a generational garbage collector, a common garbage collection
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* algorithm used in many Java virtual machine implementations,
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* manages two or more generations segregating objects by age.
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* Most of the objects are allocated in
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* the <em>youngest generation</em> (say a nursery memory pool).
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* The nursery memory pool is designed to be filled up and
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* collecting the nursery memory pool will free most of its memory space
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* since it is expected to contain mostly short-lived objects
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* and mostly are unreachable at garbage collection time.
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* In this case, it is more appropriate for the nursery memory pool
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* not to support a usage threshold. In addition,
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* if the cost of an object allocation
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* in one memory pool is very low (for example, just atomic pointer exchange),
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* the Java virtual machine would probably not support the usage threshold
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* for that memory pool since the overhead in comparing the usage with
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* the threshold is higher than the cost of object allocation.
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*
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* <p>
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* The memory usage of the system can be monitored using
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* <a href="#Polling">polling</a> or
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* <a href="#ThresholdNotification">threshold notification</a> mechanisms.
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*
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* <ol type="a">
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* <li><a name="Polling"><b>Polling</b></a>
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* <p>
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* An application can continuously monitor its memory usage
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* by calling either the {@link #getUsage} method for all
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* memory pools or the {@link #isUsageThresholdExceeded} method
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* for those memory pools that support a usage threshold.
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* Below is example code that has a thread dedicated for
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* task distribution and processing. At every interval,
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* it will determine if it should receive and process new tasks based
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* on its memory usage. If the memory usage exceeds its usage threshold,
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* it will redistribute all outstanding tasks to other VMs and
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* stop receiving new tasks until the memory usage returns
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* below its usage threshold.
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*
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* <pre>
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* // Assume the usage threshold is supported for this pool.
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* // Set the threshold to myThreshold above which no new tasks
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* // should be taken.
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* pool.setUsageThreshold(myThreshold);
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* ....
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*
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* boolean lowMemory = false;
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* while (true) {
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* if (pool.isUsageThresholdExceeded()) {
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* // potential low memory, so redistribute tasks to other VMs
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* lowMemory = true;
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* redistributeTasks();
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* // stop receiving new tasks
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* stopReceivingTasks();
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* } else {
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* if (lowMemory) {
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* // resume receiving tasks
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* lowMemory = false;
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* resumeReceivingTasks();
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* }
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* // processing outstanding task
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* ...
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* }
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* // sleep for sometime
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* try {
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* Thread.sleep(sometime);
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* } catch (InterruptedException e) {
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* ...
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* }
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* }
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* </pre>
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*
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* <hr>
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* The above example does not differentiate the case where
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* the memory usage has temporarily dropped below the usage threshold
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* from the case where the memory usage remains above the threshold
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* between two iterations. The usage threshold count returned by
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* the {@link #getUsageThresholdCount} method
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* can be used to determine
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* if the memory usage has returned below the threshold
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* between two polls.
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* <p>
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* Below shows another example that takes some action if a
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* memory pool is under low memory and ignores the memory usage
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* changes during the action processing time.
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*
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* <pre>
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* // Assume the usage threshold is supported for this pool.
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* // Set the threshold to myThreshold which determines if
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* // the application will take some action under low memory condition.
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* pool.setUsageThreshold(myThreshold);
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*
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* int prevCrossingCount = 0;
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* while (true) {
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* // A busy loop to detect when the memory usage
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* // has exceeded the threshold.
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* while (!pool.isUsageThresholdExceeded() ||
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* pool.getUsageThresholdCount() == prevCrossingCount) {
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* try {
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* Thread.sleep(sometime)
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* } catch (InterruptException e) {
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* ....
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* }
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* }
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*
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* // Do some processing such as check for memory usage
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* // and issue a warning
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* ....
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*
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* // Gets the current threshold count. The busy loop will then
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* // ignore any crossing of threshold happens during the processing.
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* prevCrossingCount = pool.getUsageThresholdCount();
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* }
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* </pre><hr>
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* </li>
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* <li><a name="ThresholdNotification"><b>Usage Threshold Notifications</b></a>
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* <p>
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* Usage threshold notification will be emitted by {@link MemoryMXBean}.
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* When the Java virtual machine detects that the memory usage of
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* a memory pool has reached or exceeded the usage threshold
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* the virtual machine will trigger the <tt>MemoryMXBean</tt> to emit an
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* {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED
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* usage threshold exceeded notification}.
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* Another usage threshold exceeded notification will not be
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* generated until the usage has fallen below the threshold and
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* then exceeded it again.
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* <p>
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* Below is an example code implementing the same logic as the
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* first example above but using the usage threshold notification
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* mechanism to detect low memory conditions instead of polling.
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* In this example code, upon receiving notification, the notification
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* listener notifies another thread to perform the actual action
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* such as to redistribute outstanding tasks, stop receiving tasks,
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* or resume receiving tasks.
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* The <tt>handleNotification</tt> method should be designed to
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* do a very minimal amount of work and return without delay to avoid
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* causing delay in delivering subsequent notifications. Time-consuming
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* actions should be performed by a separate thread.
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* The notification listener may be invoked by multiple threads
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* concurrently; so the tasks performed by the listener
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* should be properly synchronized.
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*
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* <pre>
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* class MyListener implements javax.management.NotificationListener {
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* public void handleNotification(Notification notification, Object handback) {
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* String notifType = notification.getType();
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* if (notifType.equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {
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* // potential low memory, notify another thread
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* // to redistribute outstanding tasks to other VMs
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* // and stop receiving new tasks.
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* lowMemory = true;
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* notifyAnotherThread(lowMemory);
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* }
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* }
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* }
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*
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* // Register MyListener with MemoryMXBean
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* MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();
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* NotificationEmitter emitter = (NotificationEmitter) mbean;
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* MyListener listener = new MyListener();
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* emitter.addNotificationListener(listener, null, null);
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*
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* // Assume this pool supports a usage threshold.
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* // Set the threshold to myThreshold above which no new tasks
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* // should be taken.
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* pool.setUsageThreshold(myThreshold);
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*
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* // Usage threshold detection is enabled and notification will be
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* // handled by MyListener. Continue for other processing.
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* ....
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*
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* </pre>
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* <hr>
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* <p>
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* There is no guarantee about when the <tt>MemoryMXBean</tt> will emit
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* a threshold notification and when the notification will be delivered.
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* When a notification listener is invoked, the memory usage of
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* the memory pool may have crossed the usage threshold more
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* than once.
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* The {@link MemoryNotificationInfo#getCount} method returns the number
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* of times that the memory usage has crossed the usage threshold
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* at the point in time when the notification was constructed.
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* It can be compared with the current usage threshold count returned
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* by the {@link #getUsageThresholdCount} method to determine if
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* such situation has occurred.
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* </li>
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* </ol>
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*
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* <h3><a name="CollectionThreshold">4. Collection Usage Threshold</a></h3>
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*
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* Collection usage threshold is a manageable attribute only applicable
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* to some garbage-collected memory pools.
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* After a Java virtual machine has expended effort in reclaiming memory
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* space by recycling unused objects in a memory pool at garbage collection
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* time, some number of bytes in the memory pools that are garbaged
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* collected will still be in use. The collection usage threshold
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* allows a value to be set for this number of bytes such
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* that if the threshold is exceeded,
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* a {@link MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED
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* collection usage threshold exceeded notification}
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* will be emitted by the {@link MemoryMXBean}.
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* In addition, the {@link #getCollectionUsageThresholdCount
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* collection usage threshold count} will then be incremented.
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*
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* <p>
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* The {@link MemoryPoolMXBean#isCollectionUsageThresholdSupported} method can
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* be used to determine if this functionality is supported.
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*
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* <p>
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* A Java virtual machine performs collection usage threshold checking
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* on a memory pool basis. This checking is enabled if the collection
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* usage threshold is set to a positive value.
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* If the collection usage threshold is set to zero, this checking
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* is disabled on this memory pool. Default value is zero.
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* The Java virtual machine performs the collection usage threshold
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* checking at garbage collection time.
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*
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* <p>
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* Some garbage-collected memory pools may
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* choose not to support the collection usage threshold. For example,
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* a memory pool is only managed by a continuous concurrent garbage
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* collector. Objects can be allocated in this memory pool by some thread
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* while the unused objects are reclaimed by the concurrent garbage
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* collector simultaneously. Unless there is a well-defined
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* garbage collection time which is the best appropriate time
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* to check the memory usage, the collection usage threshold should not
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* be supported.
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*
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* <p>
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* The collection usage threshold is designed for monitoring the memory usage
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* after the Java virtual machine has expended effort in reclaiming
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* memory space. The collection usage could also be monitored
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* by the polling and threshold notification mechanism
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* described above for the <a href="#UsageThreshold">usage threshold</a>
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* in a similar fashion.
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*
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* @see ManagementFactory#getPlatformMXBeans(Class)
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* @see <a href="../../../javax/management/package-summary.html">
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* JMX Specification.</a>
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* @see <a href="package-summary.html#examples">
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* Ways to Access MXBeans</a>
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*
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* @author Mandy Chung
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* @since 1.5
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*/
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public interface MemoryPoolMXBean extends PlatformManagedObject {
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/**
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* Returns the name representing this memory pool.
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*
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* @return the name of this memory pool.
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*/
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public String getName();
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/**
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* Returns the type of this memory pool.
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*
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* <p>
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* <b>MBeanServer access</b>:<br>
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* The mapped type of <tt>MemoryType</tt> is <tt>String</tt>
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* and the value is the name of the <tt>MemoryType</tt>.
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*
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* @return the type of this memory pool.
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*/
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public MemoryType getType();
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/**
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* Returns an estimate of the memory usage of this memory pool.
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* This method returns <tt>null</tt>
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* if this memory pool is not valid (i.e. no longer exists).
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*
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* <p>
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* This method requests the Java virtual machine to make
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* a best-effort estimate of the current memory usage of this
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* memory pool. For some memory pools, this method may be an
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* expensive operation that requires some computation to determine
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* the estimate. An implementation should document when
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* this is the case.
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*
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* <p>This method is designed for use in monitoring system
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* memory usage and detecting low memory condition.
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*
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* <p>
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* <b>MBeanServer access</b>:<br>
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* The mapped type of <tt>MemoryUsage</tt> is
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* <tt>CompositeData</tt> with attributes as specified in
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* {@link MemoryUsage#from MemoryUsage}.
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*
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* @return a {@link MemoryUsage} object; or <tt>null</tt> if
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* this pool not valid.
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*/
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public MemoryUsage getUsage();
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/**
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* Returns the peak memory usage of this memory pool since the
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* Java virtual machine was started or since the peak was reset.
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* This method returns <tt>null</tt>
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* if this memory pool is not valid (i.e. no longer exists).
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*
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* <p>
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* <b>MBeanServer access</b>:<br>
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* The mapped type of <tt>MemoryUsage</tt> is
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* <tt>CompositeData</tt> with attributes as specified in
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* {@link MemoryUsage#from MemoryUsage}.
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*
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* @return a {@link MemoryUsage} object representing the peak
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* memory usage; or <tt>null</tt> if this pool is not valid.
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*
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*/
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public MemoryUsage getPeakUsage();
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/**
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* Resets the peak memory usage statistic of this memory pool
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* to the current memory usage.
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*
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* @throws java.lang.SecurityException if a security manager
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* exists and the caller does not have
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* ManagementPermission("control").
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*/
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public void resetPeakUsage();
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/**
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* Tests if this memory pool is valid in the Java virtual
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* machine. A memory pool becomes invalid once the Java virtual
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* machine removes it from the memory system.
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*
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* @return <tt>true</tt> if the memory pool is valid in the running
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* Java virtual machine;
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* <tt>false</tt> otherwise.
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*/
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public boolean isValid();
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/**
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* Returns the name of memory managers that manages this memory pool.
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* Each memory pool will be managed by at least one memory manager.
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*
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* @return an array of <tt>String</tt> objects, each is the name of
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* a memory manager managing this memory pool.
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*/
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public String[] getMemoryManagerNames();
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/**
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* Returns the usage threshold value of this memory pool in bytes.
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* Each memory pool has a platform-dependent default threshold value.
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* The current usage threshold can be changed via the
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* {@link #setUsageThreshold setUsageThreshold} method.
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*
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* @return the usage threshold value of this memory pool in bytes.
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*
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* @throws UnsupportedOperationException if this memory pool
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* does not support a usage threshold.
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*
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* @see #isUsageThresholdSupported
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*/
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public long getUsageThreshold();
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/**
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* Sets the threshold of this memory pool to the given <tt>threshold</tt>
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* value if this memory pool supports the usage threshold.
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* The usage threshold crossing checking is enabled in this memory pool
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* if the threshold is set to a positive value.
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* The usage threshold crossing checking is disabled
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* if it is set to zero.
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*
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* @param threshold the new threshold value in bytes. Must be non-negative.
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*
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* @throws IllegalArgumentException if <tt>threshold</tt> is negative
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* or greater than the maximum amount of memory for
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* this memory pool if defined.
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*
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* @throws UnsupportedOperationException if this memory pool
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* does not support a usage threshold.
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*
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* @throws java.lang.SecurityException if a security manager
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* exists and the caller does not have
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* ManagementPermission("control").
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*
|
|
* @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 threshold 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 threshold);
|
|
|
|
/**
|
|
* 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();
|
|
}
|