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Threading
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method to accept an object parameter and then cast it to a string. The following example demonstrates this (the Visual Basic version is optional and provided only for consistency):
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' VB Sub GetPage(ByVal data As Object) ' Cast the object to a string Dim url As String = DirectCast(data, String) ' Request the URL Dim wr As WebResponse = WebRequest.Create(url).GetResponse() ' Display the value for the Content-Length header Console.WriteLine(url + ": " + wr.Headers("Content-Length")) wr.Close() End Sub // C# static void GetPage(object data) { // Cast the object to a string string url = (string)data; // Request the URL WebResponse wr = WebRequest.Create(url).GetResponse(); // Display the value for the Content-Length header Console.WriteLine(url + ": " + wr.Headers["Content-Length"]); wr.Close(); }
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6. Build and run the application. You will notice a couple of changes: The application runs much faster and should complete in less than half the time. The elapsed time isn t displayed correctly because it does not wait until all page requests have returned before calculating the time. You will fix this bug in Lesson 2.
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Barcode Encoder In Visual Basic .NET
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Lesson Summary
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Multithreading allows more than one method to run simultaneously. This can have several benefits, including performing processing while allowing the application to respond to user input, splitting processing between multiple processors, and improving performance by allowing multiple long-running methods (such as methods that must wait for a response from a server on the network) to run simultaneously.
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Lesson 1: Starting Multiple Threads
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You can call ThreadPool.QueueUserWorkItem to run a method in a background thread. Optionally, you can provide a single object as a parameter to the method. When you start a new thread, it is created as a background thread. Your main application continues to run in a foreground thread. Once the foreground thread has completed processing, all background threads are immediately terminated.
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Lesson Review
Painting Quick Response Code In None
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Matrix Barcode Generation In C#
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You can use the following questions to test your knowledge of the information in Lesson 1, Starting Multiple Threads. The questions are also available on the companion CD if you prefer to review them in electronic form.
NOTE
Answers
Answers to these questions and explanations of why each answer choice is right or wrong are located in the Answers section at the end of the book.
1. You need to run a method named ThreadProc in a background thread. Which code sample does this correctly A.
' VB ThreadPool.QueueUserWorkItem(AddressOf ThreadProc) // C# ThreadPool.QueueUserWorkItem(ThreadProc);
' VB ThreadPool.QueueUserWorkItem(ThreadProc) // C# ThreadPool.QueueUserWorkItem(out ThreadProc);
' VB ThreadStart.CreateDelegate(AddressOf ThreadProc) // C# ThreadStart.CreateDelegate(ThreadProc);
' VB ThreadStart.CreateDelegate(ThreadProc) // C# ThreadStart.CreateDelegate(out ThreadProc);
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Threading
2. You are creating an application that performs time-consuming calculations. You create a method named Calc that performs the calculations. You need to provide two integer values to Calc. What should you do (Each answer forms part of the complete solution. Choose all that apply.) A. Call ThreadPool.GetAvailableThreads to retrieve a handle to the thread. B. Create a custom class that contains two integer members and create an instance of that class containing the values that you need to pass to the method. C. Create a custom class that contains two integer members and a delegate for the Calc method and create an instance of that class containing the values you need to pass to the method. D. Call ThreadPool.QueueUserWorkItem and pass the Calc method and the instance of the custom class. E. Call ThreadPool.QueueUserWorkItem and pass only the instance of the custom class.
Lesson 2: Managing Threads
Lesson 2: Managing Threads
Although starting multiple threads is simple, when you begin using multiple threads in real-world applications, you ll quickly discover that simply starting a method in a background thread isn t sufficient for most practical purposes. Typically, you need to be able to receive results once processing is complete. In addition, you might need to start, pause, resume, and abort threads manually. Perhaps the most complex element of working with multiple threads is avoiding resource conflicts, which requires you to lock resources so they can be used by only one thread at a time. This lesson describes more advanced techniques for managing threads.
After this lesson, you will be able to: Start and stop threads Examine thread state Pass data to threads and receive data from threads Synchronize access to resources Wait for threads to complete Estimated lesson time: 45 minutes
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