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threads – singleton

Tuesday, August 17th, 2010

As from one of my previous posts about threading in csharp (c#), well with using Singletons you can use similar data between two different threads running.

In basics a singleton is when you want to have a single class instance so that you can share this class so that every time that you use it (even across threads) will only access the same class, it is very useful for when you have a printer spool so that you do not want to have x amount of printer spools (spool is when you have a list of print tasks waiting to print) and thus you only want to have one instance of a printer spool !!.

I have used the singleton creation from Microsoft website, that creates a singleton class that is thread safe which means that I am using the lock method that will lock on a object to stop thread contention and thus only creates a new instance of a Singleton class so that each thread will only get access to a single instance of that class.

So when you want to gain access to that single instance, you just call the

Singleton theSingleton = Singleton.Instance;

So here is the full source code, and below is the output where the output is displaying the value is incrementing otherwise if is was not a singleton class, the main class would print out 0-4 and also the runthismethod would output 0-9 instead!.

using System;
using System.Threading;
 
namespace monotestproject
{
	public sealed class Singleton
	{
		private static int _value;
		private static volatile Singleton instance;
		private static object syncRoot = new Object();
 
		public Singleton() { _value = 0;}
 
		public static Singleton Instance
		{
			get { 
				if (instance == null)
				{
					lock(syncRoot)
					{
						if (instance == null)
							instance = new Singleton();
					}
				}
				return instance;
			}
			private set {}
		}
 
		public int theValue 
		{
			get { return _value;}
			set { _value = value;}
		}
	}
 
	class MainClass
	{
		public static void Main (string[] args)
		{
			Singleton theSingleton = Singleton.Instance;
			// initialize the RunThisMethod as a thread
			Thread theThread = new Thread(RunThisMethod);
			theThread.Start();
 
			for (int j = 0; j < 5; j++)
			{
				theSingleton.theValue++;
				Console.WriteLine("Main Singleton value " + theSingleton.theValue);
				Thread.Sleep(100);
			}
		}
 
		// the method to create as a threadable method
		public static void RunThisMethod()
		{
			Singleton runsSingleton = Singleton.Instance;		
			for (int i =0; i < 10; i++)
			{
				runsSingleton.theValue++;
				Console.WriteLine("RunThisMethod Singleton value " + runsSingleton.theValue);
				Thread.Sleep(45);
			}
		}
	}
}

here is my output, as you can I am getting the singleton value incrementing, which is what should be happening.

Main Singleton value 1
RunThisMethod Singleton value 2
RunThisMethod Singleton value 3
RunThisMethod Singleton value 4
Main Singleton value 5
RunThisMethod Singleton value 6
RunThisMethod Singleton value 7
Main Singleton value 8
RunThisMethod Singleton value 9
RunThisMethod Singleton value 10
Main Singleton value 11
RunThisMethod Singleton value 12
RunThisMethod Singleton value 13
Main Singleton value 14
RunThisMethod Singleton value 15

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unsafe – pointers in the code

Friday, August 13th, 2010

Sometimes you do miss that pointer part of c++ coding within c#, well you can get around the restriction with using the unsafe syntax which basically means that you are doing some coding that please do not use the restrictions of the virtual machine and just allow direct access to the variable/memory as such.

So the basics is the

// for a block code
unsafe {
code here..
}
// or for the whole method.
public unsafe <returntype> <methodname>
{
}

So to show the code in real code, this will setup a int(eger) value to 50 and then point to the data via a pointer (*) and then you can see that the actual value within the pointer (*) is not the same and also will change every time since the int(eger) value of 50 memory location will most probably be different every time.

using System;
 
namespace unsafetest
{
    class Program
    {
        static void Main(string[] args)
        {
            unsafe
            {
                int intValue = 50;
                Console.WriteLine("integer value is : " + intValue);
                int* pointerInt = &intValue;
                Console.WriteLine("Pointer to the data is : " + *pointerInt);
                Console.WriteLine("Pointed to the memory value of data is : " + (int)pointerInt);
            }
            Console.ReadLine();
        }
    }
}

the output would be similar to, I am using a (int) cast on the memory location, which since the memory location is very big then it would be better to use something like a hex value output, but this just shows that the value will be different on different runs, if you run it again and again, that will be different values.

integer value is : 50
Pointer to the data is : 50
Pointed to the memory value of data is : 98691076

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delegates – settings function on the fly

Wednesday, June 2nd, 2010

Delegates allow a virtual method/function (static method) to be called via a link (which is the delegated variable). I have done a post before about delegates but kinder think and also have been asked how do you link one to a class and also change the delegated function due to a user input, so here goes.

I have started with setting up what type of method that I want to be associated with the delegated variable, this will be a mathematical function of either addition or subtraction with using integer values, so we need to return a integer value and also pass in two integer parameters, so a new delegated virtual method would be

public delegate int mathsOp(int value1, int value2);

and here would be a example of a method that the delegate is able to link to, because it takes 2 integer parameters and returns a integer value

public int add(int value1, int value2)
{
	return value1 + value2;
}

so we now have the delegate declaration and also a method to be able to point to, so we now need to setup the variables, one for the actual functions (MathClass that is holding the subtraction and addition methods) and also the delegated variable theMathOp that is a delegated type.

MathClass mathFunc = new MathClass();
 
mathsOp theMathOp;

to actually set the method up on the fly, you just need to tell it where you want the delegated type to point to

theMathOp = new mathsOp(mathFunc.add);

and all is needed to call the delegated type variable, well you just call it like any other method

theMathOp(inputValue1, inputValue2);

that is about it, here is the code in full that will take in some values from the user and also the user is able to choose between addition and subtraction methods

using System;
 
namespace newDelegates
{
	// a maths holding delegated function
	public delegate int mathsOp(int value1, int value2);
 
	class MathClass
	{
		// the functions to call within the class
		public int add(int value1, int value2)
		{
			return value1 + value2;
		}
 
		public int sub(int value1, int value2)
		{
			return value1 - value2;
		}
 
	}
 
	class MainClass
	{
		public static void Main (string[] args)
		{
 
			// setup the maths class which has the functions inside to call
			MathClass mathFunc = new MathClass();
 
			mathsOp theMathOp;
 
			// there is no error checking in the inputs!!
 
			Console.Write("Please enter value 1 : ");
			int inputValue1 = Convert.ToInt16(Console.ReadLine());
			Console.Write("Please enter value 2 : ");
			int inputValue2 = Convert.ToInt16(Console.ReadLine());
 
			Console.WriteLine("Please enter maths function :");
			Console.WriteLine("1 : add");
			Console.WriteLine("2 : sub");
			int mathsInputFun = Convert.ToInt16(Console.ReadLine());
			// setup the virtual function to which ever the user wants
			switch (mathsInputFun)
			{
				case 1 : 
					theMathOp = new mathsOp(mathFunc.add); 
					break;
				case 2 : 
					theMathOp = new mathsOp(mathFunc.sub); 
					break;
				default :
					Console.WriteLine("Settings to add");
					theMathOp = new mathsOp(mathFunc.add); 
					break;
			}
 
			Console.WriteLine("Value 1= " + inputValue1 + (mathsInputFun == 1 ? " + " : " - ") 
			                  + " value 2 = " + inputValue2 + " = ");
 
			// here we call the virtual function that was setup
			Console.WriteLine(theMathOp(inputValue1, inputValue2));
		}
	}
}

and below is the output of two runs of the program, one using addition and the other using subtraction

Please enter value 1 : 3
Please enter value 2 : 2
Please enter maths function :
1 : add
2 : sub
1
Value 1= 3 +  value 2 = 2 = 5
 
second run through
 
Please enter value 1 : 5
Please enter value 2 : 2
Please enter maths function :
1 : add
2 : sub
2
Value 1= 5 -  value 2 = 2 = 3

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C# – Console Parameters test

Friday, May 21st, 2010

As from my previous post on c++ console parameters, I thought that I would do one with c# (c sharp) as well, just to show the difference in the languages as well.

Compared to c++ where you cannot use the “==” (is equal to) operation because in c++ that is comparing two different memory locations and not the value within the left/right hand variables. Well in c# you can, there is a Equals method as well that you can use, but either or works fine, so in the example code below here is the main part, where I am comparing against a console parameter equalling -h (normally the help)

if (args[i].Equals("-h")) Console.WriteLine("-h option selected(equals)");
if (args[i]=="-h") Console.WriteLine("-h option selected (==)");

both of them are fine to use as you can see from the output at the bottom of the post, both will print out that “-h option selected”, best to use the Equals though.

Here is the full source code

using System;
 
namespace consoletest
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			for (int i = 0; i < args.Length; i++)
			{
				Console.WriteLine("args " + i + " : " + args[i]);								
				if (args[i].Equals("-h")) Console.WriteLine("-h option selected(equals)");
				if (args[i]=="-h") Console.WriteLine("-h option selected (==)");
			}
		}
	}
}

and here is the output using mono as the .Net runtime environment, as you can see both -h has been outputed

mono consoletest.exe -h here
args 0 : -h
-h option selected(equals)
-h option selected (==)
args 1 : here

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Threading – running different parts of the program at “once”

Friday, May 7th, 2010

A thread is when you “spawn” off another process (a process is like another program running within itself).

The operating system gives the impression that it is running allot of programs at the same time, but what is happening that allot of processes (programs) have access to the CPU for a limited amount of time, e.g. 10 milliseconds, and then leave the CPU execution stage whilst another process will enter there CPU execution stage (this is the part where the program is actually doing something).

To start with lets first create a method that is run within new thread, here we are just going to output a message and sleep for a bit, loop this over for 10 times.

// the method to create as a threadable method
public static void RunThisMethod()
{
	for (int i =0; i < 10; i++)
	{
		Console.WriteLine("RunThisMethod number : "+i.ToString() + " Sleep for 45");
		Thread.Sleep(45);
	}
}

Now lets create a thread, since a Thread has to be a delegated method but with .net 2 and above the .net environment will pick the correct delegate for you, so this means that you can just pass in the method name to the Thread class and that is it

	Thread theThread = new Thread(RunThisMethod);

To start the new Thread, it is as easy as start

	theThread.Start();

Here is the full source code, for demoing how the main and the runMyMethod flip between each other (e.g. each process has time in the processor(s) to run)

using System;
using System.Threading;
 
namespace myThread
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			// initialize the RunThisMethod as a thread
			Thread theThread = new Thread(RunThisMethod);
			theThread.Start();
 
			for (int j = 0; j < 5; j++)
			{
				Console.WriteLine("Main method number : "+j.ToString()+" Sleep for 100");
				Thread.Sleep(100);
			}
		}
 
		// the method to create as a threadable method
		public static void RunThisMethod()
		{
			for (int i =0; i < 10; i++)
			{
				Console.WriteLine("RunThisMethod number : "+i.ToString() + " Sleep for 45");
				Thread.Sleep(45);
			}
		}
	}
}

and here would be the output

Main method number : 0 Sleep for 100
RunThisMethod number : 0 Sleep for 45
RunThisMethod number : 1 Sleep for 45
RunThisMethod number : 2 Sleep for 45
Main method number : 1 Sleep for 100
RunThisMethod number : 3 Sleep for 45
RunThisMethod number : 4 Sleep for 45
Main method number : 2 Sleep for 100
RunThisMethod number : 5 Sleep for 45
RunThisMethod number : 6 Sleep for 45
Main method number : 3 Sleep for 100
RunThisMethod number : 7 Sleep for 45
RunThisMethod number : 8 Sleep for 45
Main method number : 4 Sleep for 100
RunThisMethod number : 9 Sleep for 45

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loading images on the fly

Friday, May 7th, 2010

To load a image from the server, local or remote depending if you are developing locally. I have been using monodevelop with the moonlight addin, this allows you to create silverlight applications with Linux :) .

To start with, if you create a new solution by going to File->New->Solution and then selecting the moonlight Application project as similar to creating any other new project within monodeveloper (or within visual studio if you are using visual studio to create this silver light loading images on the fly).

Moonlight mono-develop project setup

And then within your main page.xaml file you need to define where you want the image to be placed.

		<Image x:Name="Image1" Source="dot.jpeg"></Image>
		<Button x:Name="Button1" Click="ButtonClick" Height="50" Content="Click" ></Button>

above also includes the Button that you are going to click onto to load the image, in this case it will call the ButtonClick function (from the above it is the “click” method). The ButtonClick is behind the page.xaml within the page.xaml.cs file (the csharp file).

So once that button has been clicked it will call this function

		public void ButtonClick(System.Object sender,System.EventArgs eventy)
		{
			System.Windows.MessageBox.Show("hi there");
			Image1.Source = new BitmapImage(new Uri("lcd.png", UriKind.Relative));
		}

I put a little message pop up window to say “hi there”, just so that you know it have been clicked encase the lcd.png (as taken from the open clip art website here) is not in the correct place, in this case it is placed within the bin/debug, but if you are using a release edition or using visual studio you may have somewhere else.

I have included the full source code and image within a zip file above, please feel free to download.

Here is the full page.xaml if you want to look over it.

<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
             Width="500" Height="350"
             x:Class="moonlighttest.Page"
>
	<Grid x:Name="LayoutRoot" Background="Black">
		<Image x:Name="Image1" Source="dot.jpeg"></Image>
		<Button x:Name="Button1" Click="ButtonClick" Height="50" Content="Click" ></Button>
	</Grid>
</UserControl>

and here is the full page.xaml.cs file.

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;
 
namespace moonlighttest
{
 
	public partial class Page : UserControl
	{
 
		public Page ()
		{
			this.InitializeComponent ();
		}
 
		public void ButtonClick(System.Object sender,System.EventArgs eventy)
		{
			System.Windows.MessageBox.Show("hi there");
 
			Image1.Source = new BitmapImage(new Uri("lcd.png", UriKind.Relative));
		}
	}
 
}

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Web service – the consumer (client)

Thursday, April 15th, 2010

As from the web service server from the previous post you can now link to that web service. You will need to do a couple of things to be able to get the client to “talk” to the web service.

To start with on the server part of the tutorial you will need to create the dll (dynamically linked library) for the FirstWebService of the server, this is because this is what the client will use to “talk” to the server. To create this dll file you will need to compile up the FirstWebService, pull information from the server about the service and then just compile into a library

I am using mono, so if you are using .net within Windows then there is a similar command (may be just wsdl instead of wsdl2)

wsdl2 http://localhost/csharp/web_service.asmx?WSDL
 
--- output from the above command
Web Services Description Language Utility
Mono Framework v2.0.50727.1433
Writing file 'FirstWebService.cs'

as you can see it has created a file called FirstWebService.cs, a csharp source file of the WSDL (Web Services Description Language). To compile this into a FirstWebService.dll within the mono environment you just need to

gmcs /t:library FirstWebService.cs -r:System.Web.Services

the /t:library means to create a .dll file, if you do not pass in the “-r:System.Web.Services” it will complain with the below error.

FirstWebService.cs(21,51): error CS0234: The type or namespace name `Services' does not exist in the namespace `System.Web'. Are you missing an assembly reference?
Compilation failed: 1 error(s), 0 warnings

if you place the FirstWebService.dll within a bin directory within the directory where you are hosting the client from (you may need to create the bin directory for the dll)

Now it is the consumer (the client)

Since we have a FirstWebService.dll within the bin, this means that we try to compile up the client (on-the-fly) it knows how to create the class of FirstWebService. So to call the function of “Add” on the web service, we just need to create a new class of type FirstWebService and then call that function (and the rest is done behind the scenes)

    FirstWebService myFirstWebService = new FirstWebService();
    myFirstWebService.Add(4,5);

that is about it, of course it is nicer to have a web page to post some values to the server from the client, so here is the client source code, if you save this as web_service_consumer.aspx (aspx is a web page extension) and then just goto that web page hosted on the apache environment.

<%@ Page Language="C#" %>
<script runat="server">
// on the asp:Button onclick call this method
void runWebService_Click(Object sender, EventArgs e)
{
    FirstWebService myFirstWebService = new FirstWebService();
    // call the add method from the webservice
    // pass in the 2 values from the page and convert to integer values
    resultLabel.Text = myFirstWebService.Add(
		  Int32.Parse(number1.Text),
                  Int32.Parse(number2.Text)).ToString();
}
</script>
<html>
<head>
<title>ASP Web service consumer</title>
</head>
<body>
<form runat="server">
      First Number to Add : <asp:TextBox id="number1" runat="server">0</asp:TextBox>
<br/>
      Second Number To Add :
      <asp:TextBox id="number2" runat="server">0</asp:TextBox>
<br/>
      THE WEB SERVICE RESULTS!!!
<br/>
      Adding result : <asp:Label id="resultLabel" runat="server">Result</asp:Label>
<br/>
      <asp:Button id="runService" onclick="runWebService_Click" runat="server" Text="Run the Service"></asp:Button>
</form>
</body>
</html>

when you goto that page and see a error like

The type or namespace name `FirstWebService' could not be found. Are you missing a using directive or an assembly reference?
 
Source Error:
 
Line 4: void runWebService_Click(Object sender, EventArgs e)
Line 5: {
Line 6:     FirstWebService myFirstWebService = new FirstWebService();

that is because you have not created the bin directory and placed the FirstWebService.dll into that directory as describe at the top of this page.

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