Determining a thread state
This recipe will describe 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. Please 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 2012. 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:
- Start Visual Studio 2012. Create a new C# Console Application project.
- In the
Program.cs
file, add the followingusing
directives:using System; using System.Threading;
- Add the following code snippet below the
Main
method:static void DoNothing() { Thread.Sleep(TimeSpan.FromSeconds(2)); } static void PrintNumbersWithStatus() { Console.WriteLine("Starting..."); Console.WriteLine(Thread.CurrentThread .ThreadState.ToString()); for (int i = 1; i < 10; i++) { Thread.Sleep(TimeSpan.FromSeconds(2)); Console.WriteLine(i); } }
- Add the following code snippet inside the
Main
method:Console.WriteLine("Starting program..."); Thread t = new Thread(PrintNumbersWithStatus); Thread t2 = new Thread(DoNothing); Console.WriteLine(t.ThreadState.ToString()); t2.Start(); t.Start(); for (int i = 1; i < 30; i++) { Console.WriteLine(t.ThreadState.ToString()); } Thread.Sleep(TimeSpan.FromSeconds(6)); t.Abort(); Console.WriteLine("A thread has been aborted"); Console.WriteLine(t.ThreadState.ToString()); Console.WriteLine(t2.ThreadState.ToString());
- 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
Please note that the current Thread
object is always accessible through the Thread.CurrentThread
static property.
If it 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. Please 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
completed successfully and now has a ThreadState.Stopped
state. There are several other states, but they are partly deprecated and partly not as useful as those we examined.