Let’s see how we can use JProfiler to fix the memory leaks
of a Java Application. JProfiler is a
Java profiling tool targeted at
Java EE and
Java SE applications.
Profile means “drawing of the outline of anything” or
summarize (
Read interesting story about the origin of this word ) . In software engineering, profiling is a
form of dynamic program analysis that measures,
for example, the space (memory) or time complexity of a program, the usage of particular instructions, or
frequency and duration of function calls.
Let us take an example of a Java Application and try to
solve a simple memory leak with JProfiler.
1.
Install JProfiler.
2.
Create a Simple Eclipse
RCP Application with a View which has a memory leak.
3.
Run JProfiler and identify
the leak.
4.
Fix the leak.
5.
Run JProfiler again to
verify that leak is fixed.
Install JProfiler.
Download JProfiler evaluation version
http://www.ej-technologies.com/download/jprofiler/files
During installation integrate JProfiler with you eclipse.
Create a Simple Eclipse RCP Application View with a memory leak.
1. Launch your eclipse IDE with a fresh workspace.
2. Go to File --> New --> Plugin Project.
3. Give a name to the Project and Press Next.
4. Select Yes for Rich Client Application and Press Next.
5. Select RCP Application with a view as shown below and press next.
In the next window, select Add Branding and say Finish.
This will take you to a Plugin development Perspective and
your package explorer view should look something like below.
Now
to introduce a memory leak we have to make some changes to our RCP.
Open
Perspective.java and under createInitialLayout() method, delete the following line.
layout.setFixed(true);
This is to make sure that we should be able to close the
view. By default it is fixed and not closable.
Now open ApplicationActionBarAdvisor.java and override
the following method.
@Override
protected void
fillMenuBar(IMenuManager menuBar) {
IMenuManager mainMenu =
getActionBarConfigurer().getMenuManager();
MenuManager windowMenu = new MenuManager("&Window",IWorkbenchActionConstants.M_WINDOW);
mainMenu.add(windowMenu);
windowMenu.add(ActionFactory.RESET_PERSPECTIVE.create(getActionBarConfigurer().getWindowConfigurer().getWindow()));
super.fillMenuBar(menuBar);
}
This is to make sure that after closing the view, we can
bring it back by selecting the Reset Perspective Menu Action. This we need to
test memory leak.
Now to introduce the memory leak, add a new singleton class
and keep a HashMap in this singleton which stores our view as key by a strong
reference.
package rcpwithmemoryleak;
import java.util.HashMap;
import
org.eclipse.ui.part.ViewPart;
public class MemoryLeakerSingleton {
private static MemoryLeakerSingleton singleton;
HashMap<ViewPart, String> viewMap = new HashMap<ViewPart,
String>();
private
MemoryLeakerSingleton() {
}
public static MemoryLeakerSingleton
getInstance() {
if (singleton == null) {
singleton = new MemoryLeakerSingleton();
}
return singleton;
}
public void add(ViewPart v) {
viewMap.put(v, "Test");
}
}
The class should look
something like above. Now we add our
view to this map whenever we create the view. This can be done by adding a line
of code in createPartControl
method of View.java
MemoryLeakerSingleton.getInstance().add(this);
Note that this kind of scenario we face in the real word
when we use listeners or singletons which have the UI objects Hash Map. Now run your RCP application. Right Click on
the plugin and say RunAs à EclipseApplication. You should
see the application as below.
Run JProfiler and
identify the leak.
Come back to your eclipse IDE.
You should have a toolbar item called Attach with JProfiler
as shown below. Using this tool you can attach
Profiler with your running RCP application.
Click the tool and launch the Jprofiler. Open the Jprofiler
in new window. Enter the evaluation license key if you have got one.
Select the Process Name you want to profile and press OK.
In our case it is eclipse application.
By default JProfiler shows all the classes in memory. We
can view according packages as well by changing the aggregation level.
OK. Now we are
interested to see our RCP classes. It is very easy to do that. There is a View
Filter below the window where you can type the fully qualified class name or
package name to see all the classes in that package. In our case package name is rcpwithmemoryleak.
When you type this it shows all the classes.
Note that we have once instance of rcpwithmemoryleak.View.
Now you come to the RCP application and close the view by
pressing X mark on the view and then come to JProfiler and press Run GC button
on the tool bar. Now ideally after closing the view, the instance should be
collected by Garbage Collector, but you still see once instance of View as it
is being held by out Singleton Leaker.
You can reactivate the view by pressing Window à Reset Perspective. Close
again and Reactivate again. Do it for multiple times and check in the JProfiler
by Running the GC.
The second picture below shows the leak. I closed and open
the view 6 times and old instances are not cleaned up.
 |
| Memory Leak for View Object |
Now to check who is holding the view, you can take the heap
dump and analyze.
Right click on the object of interest and say “Show Selection in Heap Walker”. This
will take you to the Heap Walker.
Select the Reference Tab from the
below Tab Bar and select Incoming
References from the combo box.
You can clearly see here which is holding your View in the
memory. I used Show Paths to GC Root option to see this tree. It directly takes
you to the GC root.
Fix the leak.
Now you can go to the exact problematic point and fix your
memory leak.
In our case we can fix this in two ways.
1.
Provide remove method
in the MemoryLeakerSingleton like below
public void remove(ViewPart v) {
viewMap.remove(v);
}
Call this from the dispose() method of
View as shown below.
@Override
public void dispose() {
MemoryLeakerSingleton.getInstance().remove(this);
super.dispose();
}
2. You can make you
HashMap as WeakHashMap , then GC will automatically collect these weak
references.
Run JProfiler again to verify that leak is fixed.
Now you can run the RCP again after the code changes and
rerun the profiler and do the steps described above. You should not see any
instances if the view is closed. Your leak is fixed!
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One can use a word perfectly well under most circumstances without knowing its formal dictionary definition, but knowing that definition will certainly allow you to use it better. Knowing its etymology may bring out more nuances and connotations to the current semantics that you didn't realize are currently there. Here I've tried to give the etymology of word 'profile'.
Let’s now try to understand the etymology of word Profile. The word Profile is made up of two words: Pro and
File. Pro has been derived from Sanskrit Pra (प्र) means forth.
What about file ? Here we have a big story about it.
There
is a root word (धातु) in Sanskrit called Shi
(शि) which means Sharpen (निशाने). Based on this
root, Sanskrit has derived a word - Shira (शिरा) which means a thin vein. In Sanskrit there is a rule which
says “No difference between R and L” (रलयोरभेदः). Thus Shira
became Shila (शिला). R got kicked by L.
Now Sanskrit Shila (शिला) became
žila in Slovak and Czech (žila and shila are very close in pronunciation) carrying same meaning (vein) and in
Spanish – filón. Other few languages used this word for calling a thread or string
(since thread/ string resembles a vein). Check the words used for thread/string
in different languages below.
Italian fila, filo, filza
English used the word file.
Earlier the word file was used for communicating “a string or wire on which documents
are strung”. Now the word file means a document holder.
In this way we can say that the meaning of word Profile is before getting into details drawing an outline of the subject.
The journey of the words is really amazing!
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