JDK8/Java8源码在线阅读
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* published by the Free Software Foundation. Oracle designates this
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package java.lang.management;
import javax.management.openmbean.CompositeData;
import sun.management.MemoryUsageCompositeData;
/**
* A <tt>MemoryUsage</tt> object represents a snapshot of memory usage.
* Instances of the <tt>MemoryUsage</tt> class are usually constructed
* by methods that are used to obtain memory usage
* information about individual memory pool of the Java virtual machine or
* the heap or non-heap memory of the Java virtual machine as a whole.
*
* <p> A <tt>MemoryUsage</tt> object contains four values:
* <table summary="Describes the MemoryUsage object content">
* <tr>
* <td valign=top> <tt>init</tt> </td>
* <td valign=top> represents the initial amount of memory (in bytes) that
* the Java virtual machine requests from the operating system
* for memory management during startup. The Java virtual machine
* may request additional memory from the operating system and
* may also release memory to the system over time.
* The value of <tt>init</tt> may be undefined.
* </td>
* </tr>
* <tr>
* <td valign=top> <tt>used</tt> </td>
* <td valign=top> represents the amount of memory currently used (in bytes).
* </td>
* </tr>
* <tr>
* <td valign=top> <tt>committed</tt> </td>
* <td valign=top> represents the amount of memory (in bytes) that is
* guaranteed to be available for use by the Java virtual machine.
* The amount of committed memory may change over time (increase
* or decrease). The Java virtual machine may release memory to
* the system and <tt>committed</tt> could be less than <tt>init</tt>.
* <tt>committed</tt> will always be greater than
* or equal to <tt>used</tt>.
* </td>
* </tr>
* <tr>
* <td valign=top> <tt>max</tt> </td>
* <td valign=top> represents the maximum amount of memory (in bytes)
* that can be used for memory management. Its value may be undefined.
* The maximum amount of memory may change over time if defined.
* The amount of used and committed memory will always be less than
* or equal to <tt>max</tt> if <tt>max</tt> is defined.
* A memory allocation may fail if it attempts to increase the
* used memory such that <tt>used > committed</tt> even
* if <tt>used <= max</tt> would still be true (for example,
* when the system is low on virtual memory).
* </td>
* </tr>
* </table>
*
* Below is a picture showing an example of a memory pool:
*
* <pre>
* +----------------------------------------------+
* +//////////////// | +
* +//////////////// | +
* +----------------------------------------------+
*
* |--------|
* init
* |---------------|
* used
* |---------------------------|
* committed
* |----------------------------------------------|
* max
* </pre>
*
* <h3>MXBean Mapping</h3>
* <tt>MemoryUsage</tt> is mapped to a {@link CompositeData CompositeData}
* with attributes as specified in the {@link #from from} method.
*
* @author Mandy Chung
* @since 1.5
*/
public class MemoryUsage {
private final long init;
private final long used;
private final long committed;
private final long max;
/**
* Constructs a <tt>MemoryUsage</tt> object.
*
* @param init the initial amount of memory in bytes that
* the Java virtual machine allocates;
* or <tt>-1</tt> if undefined.
* @param used the amount of used memory in bytes.
* @param committed the amount of committed memory in bytes.
* @param max the maximum amount of memory in bytes that
* can be used; or <tt>-1</tt> if undefined.
*
* @throws IllegalArgumentException if
* <ul>
* <li> the value of <tt>init</tt> or <tt>max</tt> is negative
* but not <tt>-1</tt>; or</li>
* <li> the value of <tt>used</tt> or <tt>committed</tt> is negative;
* or</li>
* <li> <tt>used</tt> is greater than the value of <tt>committed</tt>;
* or</li>
* <li> <tt>committed</tt> is greater than the value of <tt>max</tt>
* <tt>max</tt> if defined.</li>
* </ul>
*/
public MemoryUsage(long init,
long used,
long committed,
long max) {
if (init < -1) {
throw new IllegalArgumentException( "init parameter = " +
init + " is negative but not -1.");
}
if (max < -1) {
throw new IllegalArgumentException( "max parameter = " +
max + " is negative but not -1.");
}
if (used < 0) {
throw new IllegalArgumentException( "used parameter = " +
used + " is negative.");
}
if (committed < 0) {
throw new IllegalArgumentException( "committed parameter = " +
committed + " is negative.");
}
if (used > committed) {
throw new IllegalArgumentException( "used = " + used +
" should be <= committed = " + committed);
}
if (max >= 0 && committed > max) {
throw new IllegalArgumentException( "committed = " + committed +
" should be < max = " + max);
}
this.init = init;
this.used = used;
this.committed = committed;
this.max = max;
}
/**
* Constructs a <tt>MemoryUsage</tt> object from a
* {@link CompositeData CompositeData}.
*/
private MemoryUsage(CompositeData cd) {
// validate the input composite data
MemoryUsageCompositeData.validateCompositeData(cd);
this.init = MemoryUsageCompositeData.getInit(cd);
this.used = MemoryUsageCompositeData.getUsed(cd);
this.committed = MemoryUsageCompositeData.getCommitted(cd);
this.max = MemoryUsageCompositeData.getMax(cd);
}
/**
* Returns the amount of memory in bytes that the Java virtual machine
* initially requests from the operating system for memory management.
* This method returns <tt>-1</tt> if the initial memory size is undefined.
*
* @return the initial size of memory in bytes;
* <tt>-1</tt> if undefined.
*/
public long getInit() {
return init;
}
/**
* Returns the amount of used memory in bytes.
*
* @return the amount of used memory in bytes.
*
*/
public long getUsed() {
return used;
};
/**
* Returns the amount of memory in bytes that is committed for
* the Java virtual machine to use. This amount of memory is
* guaranteed for the Java virtual machine to use.
*
* @return the amount of committed memory in bytes.
*
*/
public long getCommitted() {
return committed;
};
/**
* Returns the maximum amount of memory in bytes that can be
* used for memory management. This method returns <tt>-1</tt>
* if the maximum memory size is undefined.
*
* <p> This amount of memory is not guaranteed to be available
* for memory management if it is greater than the amount of
* committed memory. The Java virtual machine may fail to allocate
* memory even if the amount of used memory does not exceed this
* maximum size.
*
* @return the maximum amount of memory in bytes;
* <tt>-1</tt> if undefined.
*/
public long getMax() {
return max;
};
/**
* Returns a descriptive representation of this memory usage.
*/
public String toString() {
StringBuffer buf = new StringBuffer();
buf.append("init = " + init + "(" + (init >> 10) + "K) ");
buf.append("used = " + used + "(" + (used >> 10) + "K) ");
buf.append("committed = " + committed + "(" +
(committed >> 10) + "K) " );
buf.append("max = " + max + "(" + (max >> 10) + "K)");
return buf.toString();
}
/**
* Returns a <tt>MemoryUsage</tt> object represented by the
* given <tt>CompositeData</tt>. The given <tt>CompositeData</tt>
* must contain the following attributes:
*
* <blockquote>
* <table border summary="The attributes and the types the given CompositeData contains">
* <tr>
* <th align=left>Attribute Name</th>
* <th align=left>Type</th>
* </tr>
* <tr>
* <td>init</td>
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