Determining a thread state

This recipe will describe the possible states a thread could have. It is useful to get information about whether a thread is started yet or whether it is in a blocked state. Note that because a thread runs independently, its state could be changed at any time.

Getting ready

To work through this recipe, you will need Visual Studio 2015. There are no other prerequisites. The source code for this recipe can be found at BookSamples\Chapter1\Recipe5.

How to do it...

To understand how to determine a thread state and acquire useful information about it, perform the following steps:

1. Start Visual Studio 2015. Create a new C# console application project.
2. In the Program.cs file, add the following using directives:

   using System;
   using System.Threading;
   using static System.Console;
   using static System.Threading.Thread;

3. Add the following code snippet below the Main method:

   static void DoNothing()
   {
     Sleep(TimeSpan.FromSeconds(2));
   }
   
   static void PrintNumbersWithStatus()
   {
     WriteLine("Starting...");
     WriteLine(CurrentThread.ThreadState.ToString());
     for (int i = 1; i < 10; i++)
     {
       Sleep(TimeSpan.FromSeconds(2));
       WriteLine(i);
     }
   }

4. Add the following code snippet inside the Main method:

   WriteLine("Starting program...");
   Thread t = new Thread(PrintNumbersWithStatus);
   Thread t2 = new Thread(DoNothing);
   WriteLine(t.ThreadState.ToString());
   t2.Start();
   t.Start();
   for (int i = 1; i < 30; i++)
   {
     WriteLine(t.ThreadState.ToString());
   }
   Sleep(TimeSpan.FromSeconds(6));
   t.Abort();
   WriteLine("A thread has been aborted");
   WriteLine(t.ThreadState.ToString());
   WriteLine(t2.ThreadState.ToString());

5. Run the program.

How it works...

When the main program starts, it defines two different threads; one of them will be aborted and the other runs successfully. The thread state is located in the ThreadState property of a Thread object, which is a C# enumeration. At first, the thread has a ThreadState.Unstarted state. Then, we run it and assume that for the duration of 30 iterations of a cycle, the thread will change its state from ThreadState.Running to ThreadState.WaitSleepJoin.

Tip

Note that the current Thread object is always accessible through the Thread.CurrentThread static property.

If this does not happen, just increase the number of iterations. Then, we abort the first thread and see that now it has a ThreadState.Aborted state. It is also possible that the program will print out the ThreadState.AbortRequested state. This illustrates, very well, the complexity of synchronizing two threads. Keep in mind that you should not use thread abortion in your programs. I've covered it here only to show the corresponding thread state.

Finally, we can see that our second thread t2 was completed successfully and now has a ThreadState.Stopped state. There are several other states, but they are partly deprecated and not as useful as those we examined.