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mchr3k edited this page Jan 10, 2011
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InMemProfiler is a Java tool which tracks memory allocations. A number of modes can be used to help track down
- How many instances of a class are being allocated?
- What are the most common stack traces of these allocations?
- How long do these instances live?
- What class is responsible for their allocation?
Java makes it really easy to write code which allocates a lot of short lived memory (e.g. String concatenation) or to use memory structures which are larger than you might expect (e.g. Vectors). This tool allows you to quickly see find out more details about the number, size and source of object allocations.
Live objects:
56:1 - [Ljava.lang.Object;
24:1 - java.util.ArrayList
Live objects summary:
80:2
Collected objects:
0(s) - 5(s) :
440:6 - [Ljava.lang.Object;
24:1 - java.util.ArrayList
8:1 - other.test.TestObject
5(s) - 15(s) :
80:10 - other.test.TestObject
56:1 - [Ljava.lang.Object;
24:1 - java.util.ArrayList
15(s) - 25(s) :
160:20 - other.test.TestObject
112:1 - [Ljava.lang.Object;
24:1 - java.util.ArrayList
25(s) - 35(s) :
240:30 - other.test.TestObject
168:1 - [Ljava.lang.Object;
24:1 - java.util.ArrayList
35(s) - 45(s) :
45(s) - 55(s) :
55(s) - inf(s) :
Buckets summary:
472:8 - 0(s) - 5(s)
160:12 - 5(s) - 15(s)
296:22 - 15(s) - 25(s)
432:32 - 25(s) - 35(s)
0:0 - 35(s) - 45(s)
0:0 - 45(s) - 55(s)
0:0 - 55(s) - inf(s)
This output is generated from the following test program:
package test;
import java.util.ArrayList;
import java.util.List;
import other.test.TestObject;
public class Test
{
public static void main(String[] args) throws Exception
{
// Allocate 30 objects
List<TestObject> round1 = allocateObjects(30);
Thread.sleep(10 * 1000);
// Allocate 20 objects
List<TestObject> round2 = allocateObjects(20);
Thread.sleep(10 * 1000);
// Allocate 10 objects
List<TestObject> round3 = allocateObjects(10);
Thread.sleep(10 * 1000);
// Allocate 1 object, discarding 30 which are 30 seconds old
round1 = allocateObjects(1);
System.out.println(round1);
// Discard 1 object which is 0 seconds old
round1 = null;
System.out.println(round2);
// Discard 20 objects which are 20 seconds old
round2 = null;
System.out.println(round3);
// Discard 30 objects which are 30 seconds old
round3 = null;
Thread.sleep(6 * 1000);
System.out.println("===");
}
private static List<TestObject> allocateObjects(int len)
{
List<TestObject> list = new ArrayList<TestObject>();
for (int ii = 0; ii < len; ii++)
{
list.add(new TestObject());
}
return list;
}
}
Note: The extra ArrayList instance alive at the end of this code is created by a JVM system class. This will become clearer below.
This output is made possible by adding the following arguments to the JVM used to run this program.
-Xbootclasspath/a:./inmemprofiler.jar -agentpath:./inmemprofiler.dll=#bucket-5,15,25,35,45,55#gc-1#include-other,[Ljava.lang.Object,java.util.ArrayList#trackcollection
To find out more about the source of these objects you can use the #trace option to generate the following output:
Live objects:
56:1 - [Ljava.lang.Object;
Allocation Sites:
56:1
java.util.ArrayList.<init>(ArrayList.java)
java.util.ArrayList.<init>(ArrayList.java)
java.io.FilePermissionCollection.<init>(FilePermission.java)
java.io.FilePermission.newPermissionCollection(FilePermission.java)
java.security.Permissions.getPermissionCollection(Permissions.java)
java.security.Permissions.add(Permissions.java)
java.net.URLClassLoader.getPermissions(URLClassLoader.java)
sun.misc.Launcher$AppClassLoader.getPermissions(Launcher.java)
java.security.SecureClassLoader.getProtectionDomain(SecureClassLoader.java)
java.security.SecureClassLoader.defineClass(SecureClassLoader.java)
java.net.URLClassLoader.defineClass(URLClassLoader.java)
java.net.URLClassLoader.access$000(URLClassLoader.java)
java.net.URLClassLoader$1.run(URLClassLoader.java)
java.security.AccessController.doPrivileged(AccessController.java)
java.net.URLClassLoader.findClass(URLClassLoader.java)
java.lang.ClassLoader.loadClass(ClassLoader.java)
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java)
java.lang.ClassLoader.loadClass(ClassLoader.java)
Allocation Classes:
java.security.Permissions
56:1 - All methods
56:1 - add
56:1 - getPermissionCollection
java.security.SecureClassLoader
56:1 - All methods
56:1 - getProtectionDomain
56:1 - defineClass
sun.misc.Launcher$AppClassLoader
56:1 - All methods
56:1 - loadClass
56:1 - getPermissions
java.io.FilePermission
56:1 - All methods
56:1 - newPermissionCollection
java.lang.ClassLoader
56:1 - All methods
56:1 - loadClass
java.net.URLClassLoader
56:1 - All methods
56:1 - access$000
56:1 - findClass
56:1 - defineClass
56:1 - getPermissions
java.util.ArrayList
56:1 - All methods
56:1 - <init>
0:0 - add
0:0 - ensureCapacity
java.security.AccessController
56:1 - All methods
56:1 - doPrivileged
java.net.URLClassLoader$1
56:1 - All methods
56:1 - run
java.io.FilePermissionCollection
56:1 - All methods
56:1 - <init>
24:1 - java.util.ArrayList
Allocation Sites:
24:1
java.util.ArrayList.<init>(ArrayList.java)
java.io.FilePermissionCollection.<init>(FilePermission.java)
java.io.FilePermission.newPermissionCollection(FilePermission.java)
java.security.Permissions.getPermissionCollection(Permissions.java)
java.security.Permissions.add(Permissions.java)
java.net.URLClassLoader.getPermissions(URLClassLoader.java)
sun.misc.Launcher$AppClassLoader.getPermissions(Launcher.java)
java.security.SecureClassLoader.getProtectionDomain(SecureClassLoader.java)
java.security.SecureClassLoader.defineClass(SecureClassLoader.java)
java.net.URLClassLoader.defineClass(URLClassLoader.java)
java.net.URLClassLoader.access$000(URLClassLoader.java)
java.net.URLClassLoader$1.run(URLClassLoader.java)
java.security.AccessController.doPrivileged(AccessController.java)
java.net.URLClassLoader.findClass(URLClassLoader.java)
java.lang.ClassLoader.loadClass(ClassLoader.java)
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java)
java.lang.ClassLoader.loadClass(ClassLoader.java)
Allocation Classes:
java.security.Permissions
24:1 - All methods
24:1 - add
24:1 - getPermissionCollection
java.security.SecureClassLoader
24:1 - All methods
24:1 - getProtectionDomain
24:1 - defineClass
sun.misc.Launcher$AppClassLoader
24:1 - All methods
24:1 - loadClass
24:1 - getPermissions
java.io.FilePermission
24:1 - All methods
24:1 - newPermissionCollection
java.lang.ClassLoader
24:1 - All methods
24:1 - loadClass
java.net.URLClassLoader
24:1 - All methods
24:1 - access$000
24:1 - findClass
24:1 - defineClass
24:1 - getPermissions
java.util.ArrayList
24:1 - All methods
24:1 - <init>
java.security.AccessController
24:1 - All methods
24:1 - doPrivileged
java.net.URLClassLoader$1
24:1 - All methods
24:1 - run
java.io.FilePermissionCollection
24:1 - All methods
24:1 - <init>
Live objects summary:
80:2
Collected objects:
0(s) - 60(s) :
776:9 - [Ljava.lang.Object;
Allocation Sites:
552:5
java.util.Arrays.copyOf(Arrays.java)
java.util.Arrays.copyOf(Arrays.java)
java.util.ArrayList.ensureCapacity(ArrayList.java)
java.util.ArrayList.add(ArrayList.java)
test.Test.allocateObjects(Test.java)
test.Test.main(Test.java)
224:4
java.util.ArrayList.<init>(ArrayList.java)
java.util.ArrayList.<init>(ArrayList.java)
test.Test.allocateObjects(Test.java)
test.Test.main(Test.java)
Allocation Classes:
java.util.ArrayList
776:9 - All methods
552:5 - add
552:5 - ensureCapacity
224:4 - <init>
test.Test
776:9 - All methods
776:9 - allocateObjects
776:9 - main
java.util.Arrays
552:5 - All methods
552:5 - copyOf
488:61 - other.test.TestObject
Allocation Sites:
488:61
test.Test.allocateObjects(Test.java)
test.Test.main(Test.java)
Allocation Classes:
test.Test
488:61 - All methods
488:61 - allocateObjects
488:61 - main
96:4 - java.util.ArrayList
Allocation Sites:
96:4
java.util.ArrayList.<init>(ArrayList.java)
test.Test.allocateObjects(Test.java)
test.Test.main(Test.java)
Allocation Classes:
java.util.ArrayList
96:4 - All methods
96:4 - <init>
test.Test
96:4 - All methods
96:4 - allocateObjects
96:4 - main
60(s) - inf(s) :
Buckets summary:
1360:74 - 0(s) - 60(s)
0:0 - 60(s) - inf(s)
This was generated with the following set of options:
-Xbootclasspath/a:./inmemprofiler.jar -agentpath:./inmemprofiler.dll=#bucket-60#gc-1#include-other,[Ljava.lang.Object,java.util.ArrayList#trackcollection#trace
This output clearly shows that the extra ArrayList instance and corresponding Object[] comes from a call to URLClassLoader.getPermissions during classloading.
To use this tool you should download the following two files (select the appropriate dll or so file) into your application’s working directory:
You then need to add the following arguments to your java command.
Windows
-Xbootclasspath/a:./inmemprofiler.jar -agentpath:./inmemprofiler.dll
Linux
-Xbootclasspath/a:./inmemprofiler.jar -agentpath:./libinmemprofiler.so
You can specify arguments to the agent in string form e.g.
-Xbootclasspath/a:./inmemprofiler.jar -agentpath:./inmemprofiler.dll=#bucket-5,15,25,35,45,55#include-other,java.util.ArrayList#gc-1
The full list of options is described on the Profiler Options page.