blob: ecc08770a9886bf4b19db1f71b56bb10aaf4e496 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
package org.apache.qpid.junit.extensions.util;
/**
* SizeOf provides a static method that does its best to return an accurate measure of the total amount of memory used by
* the virtual machine. This is calculated as the total memory available to the VM minus the actual amount used by it.
* Before this measurement is taken the garbage collector is run many times until the used memory calculation stabilizes.
* Generally, this trick works quite well to provide an accurate reading, however, it cannot be relied upon to be totally
* accurate. It is also quite slow.
*
* <p><table id="crc"><caption>CRC Card</caption>
* <tr><th> Responsibilities <th> Collaborations
* <tr><td> Calculate total memory used.
* </table>
*
* @author Rupert Smith
*/
public class SizeOf
{
/** Holds a reference to the runtime object. */
private static final Runtime RUNTIME = Runtime.getRuntime();
/**
* Makes 4 calls the {@link #runGCTillStable} method.
*/
public static void runGCTillStableSeveralTimes()
{
// It helps to call Runtime.gc() using several method calls.
for (int r = 0; r < 4; ++r)
{
runGCTillStable();
}
}
/**
* Runs the garbage collector until the used memory reading stabilizes. It may run the garbage collector up
* to 500 times.
*/
public static void runGCTillStable()
{
long usedMem1 = usedMemory(), usedMem2 = Long.MAX_VALUE;
for (int i = 0; (usedMem1 < usedMem2) && (i < 500); ++i)
{
RUNTIME.runFinalization();
RUNTIME.gc();
Thread.currentThread().yield();
usedMem2 = usedMem1;
usedMem1 = usedMemory();
}
}
/**
* Runs the garbage collector until the used memory stabilizes and then measures it.
*
* @return The amount of memory used by the virtual machine.
*/
public static long getUsedMemory()
{
runGCTillStableSeveralTimes();
return usedMemory();
}
/**
* Returns the amount of memory used by subtracting the free memory from the total available memory.
*
* @return The amount of memory used.
*/
private static long usedMemory()
{
return RUNTIME.totalMemory() - RUNTIME.freeMemory();
}
}
|
