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Constructing a Thread object is a relatively lightweight operation because it does not actually create a physical operating system thread . To actually create the operating system thread and have it start executing the callback method, you must call Thread s Start method, passing into it the object (state) that you want passed as the callback method s argument . The following code demonstrates how to create a dedicated thread and have it call a method asynchronously:
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using System; using System.Threading; public static class Program { public static void Main() { Console.WriteLine("Main thread: starting a dedicated thread " + "to do an asynchronous operation"); Thread dedicatedThread = new Thread(ComputeBoundOp); dedicatedThread.Start(5); Console.WriteLine("Main thread: Doing other work here..."); Thread.Sleep(10000); // Simulating other work (10 seconds) dedicatedThread.Join(); // Wait for thread to terminate Console.WriteLine("Hit <Enter> to end this program..."); Console.ReadLine(); } // This method's signature must match the ParameterizedThreadStart delegate private static void ComputeBoundOp(Object state) { // This method is executed by a dedicated thread Console.WriteLine("In ComputeBoundOp: state={0}", state); Thread.Sleep(1000); // Simulates other work (1 second) // When this method returns, the dedicated thread dies } }
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When I compile and run this code, I get the following output:
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Main thread: starting a dedicated thread to do an asynchronous operation Main thread: Doing other work here... In ComputeBoundOp: state=5
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Sometimes when I run this code, I get the following output since I can t control how Windows schedules the two threads:
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Main thread: starting a dedicated thread to do an asynchronous operation In ComputeBoundOp: state=5 Main thread: Doing other work here...
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Notice that the Main method calls Join . The Join method causes the calling thread to stop executing any code until the thread identified by dedicatedThread has destroyed itself or been terminated .
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Part V
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Threading
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Reasons to use Threads
There are really three reasons to use threads .
You can use threads to isolate code from other code . This can improve your application s reliability, and in fact, this is why Windows introduced the concept of threads into the operating system . Windows needs threads for reliability because your application is a third-party component to the operating system and Microsoft doesn t verify the quality of your code before you ship it . However, you should be testing all of your applications before you ship them, and since you are testing complete applications, you should know that they are robust and of high quality . Because of this, your application s need for robustness is not as high as the operating system s need for robustness, and therefore, your application should not use many threads for the purpose of maintaining robustness . If your application supports the loading of components produced by other parties, then your application s need for robustness increases and using threads can help satisfy this requirement . You can use threads to make your coding easier . Sometimes coding is easier if you execute a task via its own thread . But of course, when you do this, you are using additional resources and not writing the code as efficiently as possible . Now, I m all for having an easier coding process even at the expense of some resources . If I weren t OK with this, then I d still be writing in machine language as opposed to being a C# developer . But sometimes I see people using threads thinking that they are choosing an easier programming methodology when, in fact, they are complicating their life (and their code) substantially . Usually, when you introduce threads, you introduce coordination code that may require thread synchronization constructs to know when the other thread has terminated . Once you start handling coordination, you are using even more resources and complicating your code . So make sure that threads are really going to help you before you start using them . You can use threads to get concurrent execution . If and only if you know that your application is running on a machine with multiple CPUs in it, you can get improved performance by having multiple tasks executing simultaneously . Today, machines with multiple CPUs in them are quite common, so designing your application to use multiple cores makes sense and is the focus of 26 and 27, I/O-Bound Asynchronous Operations .
Now, I d like to share with you a theory of mine . Every computer has an incredibly powerful resource inside it: the CPU itself . If someone spends money on a computer, then that computer should be working all the time . In other words, I believe that all the CPUs in a computer should be running at 100 percent utilization all the time . I will qualify this statement with two caveats . First, you may not want the CPUs running at 100 percent utilization if the computer is on battery power because that may drain the battery too quickly . Second, some data centers would prefer to have 10 machines running at 50 percent CPU utilization rather than
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