Threads

 

Threads give the appearance that an application is performing multiple tasks in parallel. Threads live in one process and take individual paths of execution. Threads have different priorities, such as REAL-TIME, HIGH, NORMAL, and IDLE.. The CPU will run the threads with higher priorities first causing one thread to never get a chance to run; this is called starvation. There are three thread states – running, ready, and blocked. Running means that the thread is already running; ready means that the thread is out of the blocked state and is ready for the available resources so that it can move to the running state; and blocked means that the thread cannot run. Blocked threads can never go straight to running; they must be ready first. To better understand threads, here’s an example. Take in two numbers from the user. The first number will be the number of threads to create and run, and the second number will be the amount of time, in milliseconds, for each thread to sleep. When each one of those threads is created, have it print that it is alive and then tell it to sleep.

 

Thread Creation: 

To create a thread, you first need to tell the compiler that you will be using System.Threading.  Create a variable of type Thread and tell it to get a new Thread, and tell it what procedure for which the thread will be responsible.  After you finish creating the thread, tell it to start running by using the Start() command.

 

Your code to solve the problem stated in the intro should look similar to the code below (the highlighted code is the code needed to create a thread).

 

using System; using System.Threading;   namespace Threads {       /// <summary>       /// Summary description for Class1.       /// </summary>       class ThreadMe       {             private static int threadNumber = 1;             private static int sleepLeng = 0;             private static Thread [] myThreads;             /// <summary>             /// The main entry point for the application.             /// </summary>             [STAThread]             static void Main(string[] args)             {                   Console.Write("Please enter the number of threads you wish to generate: ");                   int numberOfThreads = Int32.Parse(Console.ReadLine());                   myThreads = new Thread[numberOfThreads];                   Console.Write("How long do you want the threads to sleep?: ");                   sleepLeng = Int32.Parse(Console.ReadLine());                    StartThreads(numberOfThreads);             }             static void StartThreads (int numThreads)             {                       for (int i = 0; i < numThreads; i++)                   {                                         Thread theThread = new Thread (new ThreadStart (StartFunction));                         theThread.Start();                         myThreads[i] = theThread;                   }                       }             static void StartFunction ()             {                   Console.WriteLine ("Thread " + threadNumber + " is alive.");                   int threadNum = threadNumber;                   threadNumber++;                   Console.WriteLine ("Thread " + threadNum + " is sleeping.");                   Thread.Sleep(sleepLeng);                   Console.WriteLine ("Thread " + threadNum + " is awake.");             }       } }

 

As the problem in the lab intro stated, the above application needs to prompt the user for the number of threads to create and the amount of time the threads should sleep.  This is accomplished through the use of the Console.Write and Console.ReadLine commands (remember that each time you try to read in from the Console, it returns a String. In this case, you want an int. You will need to use the Int32.Parse command to convert the String to an int.  Now that we have the needed information from the user, it is time to move on to the creation of our threads.  Again, this means we will need to tell the compiler we are using System.Threading. Create the thread and tell it the procedure it is responsible for executing, and start the thread.  To create and start our threads we will need to use the code found below:

 

Thread theThread = new Thread (new ThreadStart (StartFunction)); theThread.Start();

 

As you can see in our application code, the above code segment is found within a for loop. Remember, rather than creating just one thread, we will be creating multiple threads.  Thus, by putting the above code in a loop, we are able to spawn off as many threads as needed and place them in our array of threads.  Also in our application code, the size of the array is determined at run time by the number of threads the user wants to create.  Also the procedure that each thread will be responsible for executing is the StartFunction procedure. This procedure will print out the necessary information to the user and will also tell the thread to sleep for the established length of time (processing cycles).