Threading Walkthrough(.NET)

Walk Through Threading in C#:
After a long time I got a chance to write,I felt this is the topic to be most required to discuss,below simple & I would say light weight data would make you to digest threading concepts in C#,

A thread is defined as the execution path of a program. Each thread defines a unique flow of control.

With the help of threads we can increase the response time of the application.

Thread Life Cycle

The life cycle of a thread starts when an object of the System.Threading.Thread class is created and ends when the thread is terminated or completes execution.

Following are the various states in the life cycle of a thread:

The Unstarted State: it is the situation when the instance of the thread is created but the Start method has not been called.
The Ready State: it is the situation when the thread is ready to run and waiting CPU cycle.
The Not Runnable State: a thread is not runnable, when:

Sleep method has been called
Wait method has been called
Blocked by I/O operations

The Dead State: it is the situation when the thread has completed execution or has been aborted.

The Main Thread:

System.Threading.Thread class is used for working with threads.

When a C# program starts execution, the main thread is automatically created.

You can access a thread using the CurrentThread property of the Thread class.

Nice Example illustrates you the point:

static void Main(string[] args)
{

                             Thread th = Thread.CurrentThread;
                             th.Name = "MainThread";
                             Console.WriteLine("This is {0}", th.Name);
                             Console.ReadKey();
                   }

o/p: This is MainThread

Creating Threads:

Threads are created by extending the Thread class. The extended Thread class then calls the Start() method to begin the child thread execution.

The following program demonstrates the concept:

   class Program
          {
                   public static void CallToChildThread()
                   {
                             Console.WriteLine("Child thread starts");
                   }

                   static void Main(string[] args)
                   {
                             ThreadStart childref = new ThreadStart(CallToChildThread);
                             Console.WriteLine("In Main: Creating the Child thread");
                             Thread childThread = new Thread(childref);
                             childThread.Start();
                             Console.ReadKey();
                   }

}

o/p:   In Main: Creating the Child thread

         Child thread starts

Managing Threads:

public static void CallToChildThread()

{

Console.WriteLine("Child thread starts");

// the thread is paused for 5000 milliseconds

int sleepfor = 5000;

Console.WriteLine("Child Thread Paused for {0} seconds",

sleepfor / 1000);

Thread.Sleep(sleepfor);

Console.WriteLine("Child thread resumes");

}
static void Main(string[] args)
{
ThreadStart childref = new ThreadStart(CallToChildThread);
Console.WriteLine("In Main: Creating the Child thread");
Thread childThread = new Thread(childref);
childThread.Start();
Console.ReadKey();
}

O/p:

Destroying Threads:

The Abort() method is used for destroying threads.

The runtime aborts the thread by throwing a ThreadAbortException. This exception cannot be caught, the control is sent to the finally block, if any.

public static void CallToChildThread()
{
try

{
Console.WriteLine("Child thread starts");
// do some work, like counting to 10
for (int counter = 0; counter <= 10; counter++)
{
Thread.Sleep(500);
Console.WriteLine(counter);
}

//So here in this child thread it makes 3 trips (after every 500 ms..when it starts doning for 4th
//Main thread Sleep time got copleted so main thread become active
Console.WriteLine("Child Thread Completed");

}
catch (ThreadAbortException e)
{
Console.WriteLine("Thread Abort Exception");
}
finally
{
Console.WriteLine("Couldn't catch the Thread Exception");
}
}
static void Main(string[] args)
{
ThreadStart childref = new ThreadStart(CallToChildThread);
Console.WriteLine("MainThread: Creating the Child thread");
Thread childThread = new Thread(childref);
childThread.Start();
//stop the main thread for some time
//For this period Child thread will execute
Thread.Sleep(2000);
//now abort the child
Console.WriteLine("MainThread: Aborting the Child thread");
childThread.Abort();
Console.ReadKey();
}

O/p:

Let us observe the below examples:

Ex:

class Program
{
static void Main()
{
Thread t = new Thread(WriteY); // Kick off a new thread
t.Start(); // running WriteY()
//Thread.Sleep(1000);
// Simultaneously, do something on the main thread.
for (int i = 0; i < 100; i++)
Console.Write("x");
Console.ReadKey();
}
static void WriteY()
{
for (int i = 0; i < 100; i++) Console.Write("y");
}
}

O/p:

xxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyy
yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
yyyyyyyyyyyyyxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
...

The main thread creates a new thread t on which it runs a method that repeatedly prints the character “y”. Simultaneously, the main thread repeatedly prints the character “x”:

I have commented Thread.Sleep(1000),if you uncomment it then the Main Thread will be in sleep mode in that time writeY thread got executed,Just test it to know….

Ex:

static bool done; // Static fields are shared between all threads
static void Main()
{
//new Thread(Go).Start();
//Go();//if your using static keyword for Go()
Program tt = new Program(); // Create a common instance
new Thread(tt.Go).Start();
tt.Go();
Console.Read();
}
void Go()
{
if (!done) { done = true; Console.WriteLine("Done");
}
}

O/p:

Done

If you just Do Swap under if statement:like this

void Go()
{
if (!done) { Console.WriteLine("Done"); done = true; }
}
Then out put changes to :
O/p:

Done

Now,you would feel oohhh..!! How can it be..???

The problem is that one thread can be evaluating the

 if statement right as the other thread is executing the WriteLine statement —

before it’s had a chance to set done to true.

How to avoid..??

The remedy is to obtain an  lock while reading and writing to the common field.

 C# provides the lock statement for this purpose.

Below same program with lock get fixes your problem:

Ex:

static bool done;    // Static fields are shared between all threads
static readonly object locker = new object();
static void Main()
{
//new Thread(Go).Start();
//Go();                  //if your using static method for Go() then this is correct
Program tt = new Program();   // Create a common instance
new Thread(tt.Go).Start();
tt.Go();
Console.Read();
}
void Go()
{
lock (locker)
{
if (!done) { Console.WriteLine("Done"); done = true; }
}
}

Join and Sleep:

As you know Sleep() is used to stop the thread and simultaneously other thread got executed but For ex: If I don’t know at what time should this thread A need to be kept in sleep mode to execute thread B,then after starting thread A just use Join() then thread B after completion automatically returns to the state where it was started and execute the remaining statement in thread B.

Ex:

static void Main()
{
Thread t = new Thread(Go);
t.Start();
t.Join();
Console.WriteLine("Thread t has ended!");
Console.Read();
}
static void Go()
{
for (int i = 0; i < 2; i++) Console.Write("y");
}

This prints “y” 1,000 times, followed by “Thread t has ended!” immediately afterward.

Pass Data to the thread in this way:

Ex:

static void Main()
{
Thread t = new Thread(() => Print("Hello from t!"));
t.Start();
Console.Read();
}

static void Print(string message)
{
Console.WriteLine(message);
}

With this approach, you can pass in any number of arguments to the method. You can even wrap the entire implementation in a multi-statement lambda:
Ex:
new Thread (() =>
{
Console.WriteLine ("I'm running on another thread!");
Console.WriteLine ("This is so easy!");

}).Start();
Now let us discuss Multithreading:

Multi Threading:

There is not a big deal in understanding Multi threading after above examples, for a long time, most programming applications (except for embedded system programs) were single-threaded. That means there was only one thread in the entire application. You could never do computation A until completing computation B.

But,Multi threading allows you to do the Computations at a time. Then surely it makes your performance twice.

Below Example illustrates you the Multi Threading concept, Handling of the threads in Multithreading can be done in difference way

(Note: Uncomment the statements to understand more about handling threads by setting through prority,locks..)

//static readonly object locker = new object();
public static void Thread1()
{
//lock (locker)
//{
for (int i = 0; i < 5; i++)
{
Console.WriteLine("Thread1 Task-{0} Finished", i);
}
//}
}
public static void Thread2()
{
//lock (locker)
//{
for (int i = 0; i < 5; i++)
{
Console.WriteLine("Thread2 Task-{0} Finished", i);
}
//}
}
}
public class MyClass
{
public static void Main()
{
Console.WriteLine("Before start thread");
Thread tid1 = new Thread(new ThreadStart(MyThread.Thread1));
Thread tid2 = new Thread(new ThreadStart(MyThread.Thread2));
//tid2.Priority = ThreadPriority.Highest;
tid1.Start();
tid2.Start();
Console.ReadKey();
}
O/p:

Friends I hope you have got an idea about threading now….

there are still many things to discuss in this topic but ,

I would feel these is enough to start.

Thursday, January 16, 2014