 marked with ThreadStaticAttribute is not shared between threads. Each executing thread has a separate instance of the field, and independently sets and gets values for that field. If the field is accessed on a different thread, it will contain a different value.
Note that in addition to applying the ThreadStaticAttribute attribute to a field, you must also define it as a static field (in C#) or a Shared field (in Visual Basic).
Use this attribute as it is, and do not derive from it.
For more information about using attributes, see Extending Metadata Using Attributes.
The following example instantiates a random number generator, creates ten threads in addition to the main thread, and then generates two million random numbers in each thread. It uses the ThreadStaticAttribute attribute to calculate the sum and the count of random numbers per thread. It also defines two additional per-thread fields, previous and abnormal, that allows it to detect corruption of the random number generator.
using System; using System.Threading; public class Example { [ThreadStatic] static double previous = 0.0; [ThreadStatic] static double sum = 0.0; [ThreadStatic] static int calls = 0; [ThreadStatic] static bool abnormal; static int totalNumbers = 0; static CountdownEvent countdown; private static Object lockObj; Random rand; public Example() { rand = new Random(); lockObj = new Object(); countdown = new CountdownEvent(1); } public static void Main() { Example ex = new Example(); Thread.CurrentThread.Name = "Main"; ex.Execute(); countdown.Wait(); Console.WriteLine("{0:N0} random numbers were generated.", totalNumbers); } private void Execute() { for (int threads = 1; threads <= 10; threads++) { Thread newThread = new Thread(new ThreadStart(this.GetRandomNumbers)); countdown.AddCount(); newThread.Name = threads.ToString(); newThread.Start(); } this.GetRandomNumbers(); } private void GetRandomNumbers() { double result = 0.0; for (int ctr = 0; ctr < 2000000; ctr++) { lock (lockObj) { result = rand.NextDouble(); calls++; Interlocked.Increment(ref totalNumbers); // We should never get the same random number twice. if (result == previous) { abnormal = true; break; } else { previous = result; sum += result; } } } // get last result if (abnormal) Console.WriteLine("Result is {0} in {1}", previous, Thread.CurrentThread.Name); Console.WriteLine("Thread {0} finished random number generation.", Thread.CurrentThread.Name); Console.WriteLine("Sum = {0:N4}, Mean = {1:N4}, n = {2:N0}\n", sum, sum/calls, calls); countdown.Signal(); } } // The example displays output similar to the following: // Thread 1 finished random number generation. // Total = 1,000,556.7483, Mean = 0.5003, n = 2,000,000 // // Thread 6 finished random number generation. // Total = 999,704.3865, Mean = 0.4999, n = 2,000,000 // // Thread 2 finished random number generation. // Total = 999,680.8904, Mean = 0.4998, n = 2,000,000 // // Thread 10 finished random number generation. // Total = 999,437.5132, Mean = 0.4997, n = 2,000,000 // // Thread 8 finished random number generation. // Total = 1,000,663.7789, Mean = 0.5003, n = 2,000,000 // // Thread 4 finished random number generation. // Total = 999,379.5978, Mean = 0.4997, n = 2,000,000 // // Thread 5 finished random number generation. // Total = 1,000,011.0605, Mean = 0.5000, n = 2,000,000 // // Thread 9 finished random number generation. // Total = 1,000,637.4556, Mean = 0.5003, n = 2,000,000 // // Thread Main finished random number generation. // Total = 1,000,676.2381, Mean = 0.5003, n = 2,000,000 // // Thread 3 finished random number generation. // Total = 999,951.1025, Mean = 0.5000, n = 2,000,000 // // Thread 7 finished random number generation. // Total = 1,000,844.5217, Mean = 0.5004, n = 2,000,000 // // 22,000,000 random numbers were generated.
The example uses the lock statement in C# and the SyncLock construct in Visual Basic to synchronize access to the random number generator. This prevents corruption of the random number generator, which typically results in its returning a value of zero for all subsequent calls.
The example also uses the CountdownEvent class to ensure that each thread has finished generating random numbers before it displays the total number of calls. Otherwise, if the main thread completes execution before the additional threads that it spawns, it displays an inaccurate value for the total number of method calls.
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