Monday, March 25, 2013

Performance Counters Testing Tool

Writing high performance applications, specially that does batch processing is always fun. But most of the time you are unaware of whats going on under the hood.

You can use Performance Counter in Windows to find out how many threads your process has spawned, whats the current CPU and/or memory usage. But what if you want to know whats going on in your logic and with what frequency ?

For that you need to "Post" performance data out to windows operating system. So you could watch/log the data in order to generate nice and fancy reports for the superiors.

This post is all about sharing Performance Data Testing Tool that I built and would like to share. If you want to learn more about Windows Performance Counters, Check this Microsoft Article.

To learn the basics about how to code in .NET to post performance data to windows system, check this guy's  Blog Post Part 1 and Part 2.

Go to the Google Code project page to download binary or source code for the Tool.

Here is a snapshot

"Play with existing" part lets you change the values for current number of current counters that are being posted.

"Create/Delete" lets you create your own category and add counters to them. Once you've created new category with at least one counter, you can type the category name and counter name on the above section and click the Top Grab button then you can use Increment/Decrement button to up and down the values.

To watch those values in a graph, use Windows Performance Monitor.

You are free to use my code, modify it and/or redistribute it.

Happy coding

Monday, March 18, 2013

iOS app development for C/C++/C# Developers : Defining default constructor in Objective-C

In this post I am going to share how we do whats called "constructors" in C++ or C# and for my C-only fellows, object initializers or <insert some term here>.

As I mentioned in my previous blog post that Objective-C has no such thing as constructors. We use the native non-instance method or what we call "static" method to allocate a new instance. That method is called alloc.

 MyClass* myObj = [MyClass alloc]

The above code just creates an object in a fashion similar to having no constructors defined in our C++ or C# class.

But consider the following code in C++.

 class Circle
    private int m_radius;
    public Circle()
       m_radius = 10; // C++ folks can also use the "initializer list" for this assignment

If we want to implement the same logic in Objective-C, we are going to have to define something what most Obj-C developers call "initializers"

Initializers are nothing but methods that may take arguments and meant to be called right after allocation of a new object. So we could do the following in Objective-C. Lets do a "default constructor" in this post. I will make another post for parameter-ized constructor

Circle.h file
 #import <foundation/foundation.h>

@interface Circle : NSObject {
  NSInteger m_radius;

 - (id) init;

Circle.m file
 @implementation Circle
  - (id) init
    self = [super init]; // calling base class's init in this case NSObject's init

    if (self) { // checking to see if an object has been returned by NSObject's init
            self.m_radius = 10; // set the default value to 10
   return self; // In order for it to act like a constructor, it should return the object

And this is how we create an object using the initializer defined above
 Circle* circleObj = [[Circle alloc] init];

By the way, 'super' is a Java term for base class too. Somebody gets a title of 'copy-cat' here.

That's all folks for this post. Please let me know your comments in the comment box below if you have any.

Google Drive outage made my presentation go the wrong way

Update: Drive is back up but too late.

Had embarrassing and frustrating moments when I had to screen a presentation off my Google Drive account and I saw the ridiculous error message with picture of a broken monkey with a wrench
"502, Thats an error The server encountered a temporary error and could not complete your request.. Please try again in 30 seconds, Thats all we know"

And their Apps Dashboard showing the following message, which scared my audience away from idea of using Google stuff for our business.

And a lot of people blowing off their steams at the wrong place,  Google Drive Forum

Lets see how this drama ends, but I am sure missing the deadline because of this outage. I wish I had downloaded updated copies of all my docs from the drive every night as a backup to my local drive.

Please be mindful of these imminent issues when choosing such kind of services for your business.

Tuesday, March 12, 2013

A few Objective-C kick start tips for C++ Developers

Here are a few things I as a C++ developer had to learn the hard way.

Basic Language Constructs

+ sign for static methods - sign for methods that require objects

For instance in C++ we do the following
static void SomeMethod();

The objective-C equivalent would be

+(void) SomeMethod;

Similarly for non-static methods just change the + sign to -. They are called Instance Methods.

-(void) SomeNonStaticMethod;

You may also have noticed that the return type is enclosed in () parenthesis which was weird to me.

No private methods

Thats right, no method is private. You can have member variables or attributes private by using @private but methods cannot be private.

Method calling

In C++ we have, when we have to call a method; we do


In Objective-C, its totally changed. 

[myObj MethodName];

Tada! No Constructor

Yes, there is no such thing as constructor. All you do is call a native/built-in method alloc to create an object with default properties.

[MyClass alloc]; //Here is the object being created

But Objective-C developers have come up with something called initializers, so immediately after the object is created, an init method is called. Keep in mind that init is something developer has to create as a method that does some initialization work.

[ [MyClass alloc] init];

Weird asterisk * that reminds you of pointer will get on your nerve

Yes, that asterisk is for pointers. Every object reference is stored in pointers. 

So in C++ we create objects by simply writing the following code

MyClass MyObj = MyClass();

In Objective-C, you will have to write the following code
MyClass *MyObj = [ [ MyClass alloc ] init];

Project files

Objective-C has similar to .h/.cpp structure for class declaration and definition but its most often called .h/.m or .h/.mm (for Objective-C++)

Keyword interface is not what you think

interface keyword in Objective-C is used for class declarations.

C++ code
class MyClass





Objective-C will require you to write the following code for the above

@interface MyClass {

// non-static variables go here


- (MyClass*) init;


Class definition or .m file

.m file or .cpp file counterpart in Objective-C would look something like this

@implementation MyClass { // Yes 'class' keyword is never seen

-(MyClass*) init  {

 if (self) {

// initialize self here


return self;



Thats all folks! There is more information on the topic which I intend to write in future blog posts. If you are a C++ developer and thinking about taking a nosedive into Objective-C, above mentioned things should be enough for you to brace for.

I would love to hear your comments. They help me understand how useful my postings are.

Sunday, March 10, 2013

WPF - How to run XPath count() in XmlDataProvider binding

Welcome to my very first (not really) blogging entry. I was monkeying around with an issue on internet and could not find any solution, however, I did find quite a few people looking for the same thing I was looking for. I tried something that worked, thought I would share that with the world.

So the issue is, You have the following Xml to bind to in your WPF application

  <Book Name="WPF Basics" Author="John Doe">  
     <Name>Wrox </Name>  
     <Name>Microsoft Press</Name>  
  <Book Name="Thinking in WPF" Author="Johny Cage">  
     <Name>Wrox </Name>  

Now you have a Listview that displays Book name in one column and number of Publishers in other column.

If WPF XmlDataProvider supported XPath functions you could do something like this for 2nd column

{Binding XPath=count(Publishers/Publisher)}

But XmlProvider binding uses SelectNodes() of XmlNode in System.Xml which does not take XPath functions.

Another way I was able to think of was to use converters and do something like this

{Binding XPath=Publishers/Publisher, Converter=myOwnNodeListToCountConverter}

But XmlDataProvider calls the .ToString() before passing it on to your converter. Which means, your converter won't get an XmlNodeList object, but just an empty string.

So lastly, I tried this which finally worked, Not an elegant way but it works. :)

The basic idea is to render all the items you want to count in an invisible (Visibility=Collapsed) ItemsControl and Bind a TextBlock to the Items.Count of that ItemsControl. Here is a little snippet to show the concept.

<ListView IsSynchronizedWithCurrentItem="True" Margin="8,8,0,0" ItemsSource="{Binding Source={StaticResource xmlFmlDataSource}, XPath=//Programs/Program, Mode=OneWay}">
                    <GridViewColumn Header="Book name" Width="200" DisplayMemberBinding="{Binding XPath=@Name}"  >
                    <GridViewColumn Header="Params" Width="50" >
                                <ItemsControl x:Name="dummyItemsControl" ItemsSource="{Binding XPath=Publishers/Publisher}" Visibility="Collapsed">
                                            <TextBlock Text="" />
                                <TextBlock Text="{Binding ElementName=dummyItemsControl, Path=Items.Count}" />

This is not my dream solution that I feel ecstatic about, but this works and won't probably a big deal if the data volume is not too large. I would love to read your comments.