Creating multiple threads

Sometimes, we need to create multiple threads. Before we can continue, however, we need to wait for these threads to complete doing whatever they need to do. For this, the use of tasks is best suited.

Getting ready

Make sure that you have added the using System.Threading.Tasks; statement to the top of your Recipes class.

How to do it…

  1. Create a new method called MultipleThreadWait() in your Recipes class. Then, create a second method called RunThread() with the private modifier, which takes an integer of seconds to make the thread sleep. This will simulate the process of doing some work for a variable amount of time:
    public class Recipes
{
    public void MultipleThreadWait()
    {        

    }

    private void RunThread(int sleepSeconds)
    {        

    }
}

    Note

    In reality, you would probably not call the same method. You could, for all intents and purposes, call three separate methods. Here, however, for the sake of simplicity, we will call the same method with different sleep durations.

  2. Add the following code to your MultipleThreadWait() method. You will notice that we are creating three tasks that then create three threads. We will then fire off these three threads and make them sleep for 3, 5, and 2 seconds. Finally, we will call the Task.WaitAll method to wait before continuing the execution of the application:
    Task thread1 = Task.Factory.StartNew(() => RunThread(3));
Task thread2 = Task.Factory.StartNew(() => RunThread(5));
Task thread3 = Task.Factory.StartNew(() => RunThread(2));

Task.WaitAll(thread1, thread2, thread3);
WriteLine("All tasks completed");
  3. Then, in the RunThread() method, we will read the current thread ID and then make the thread sleep for the amount of milliseconds supplied. This is just the integer value for the seconds multiplied by 1000:
    int threadID = Thread.CurrentThread.ManagedThreadId;

WriteLine($"Sleep thread {threadID} for {sleepSeconds} seconds at {DateTime.Now.Second} seconds");
Thread.Sleep(sleepSeconds * 1000);
WriteLine($"Wake thread {threadID} at {DateTime.Now.Second} seconds");
  4. When you have completed the code, your Recipes class should look like this:
    public class Recipes
{
    public void MultipleThreadWait()
    {
        Task thread1 = Task.Factory.StartNew(() => RunThread(3));
        Task thread2 = Task.Factory.StartNew(() => RunThread(5));
        Task thread3 = Task.Factory.StartNew(() => RunThread(2));

        Task.WaitAll(thread1, thread2, thread3);
        WriteLine("All tasks completed");
    }

    private void RunThread(int sleepSeconds)
    {
        int threadID = Thread.CurrentThread.ManagedThreadId;

        WriteLine($"Sleep thread {threadID} for {sleepSeconds} seconds at {DateTime.Now.Second} seconds");
        Thread.Sleep(sleepSeconds * 1000);
        WriteLine($"Wake thread {threadID} at {DateTime.Now.Second} seconds");
    }
}
  5. Finally, add a new instance of the Recipe class to your console application and call the MultipleThreadWait() method:
    Chapter7.Recipes oRecipe = new Chapter7.Recipes();
oRecipe.MultipleThreadWait();
Console.ReadLine();
  6. Run your console application and view the output produced:
    How to do it…

How it works…

You will notice that three threads (thread 9, thread 10, and thread 11) are created. These are then paused by making them sleep for various amounts of time. After each thread wakes, the code waits for all three threads to complete before continuing the execution of the application code.

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