`Parallel.Invoke`

A program needs to do many things, and the order they occur is not important. Instead of using complicated threading logic, we can use Parallel.Invoke.

Part of System.Threading.Tasks, Parallel.Invoke is a simple method to use. We pass Actions to it. The name of a static void method will work as an Action.

This program introduces 3 test methods: Test, Test 2, and Test 3. We make sure the add "using System.Threading.Tasks" to the top of the program.

Start We call Parallel.Invoke with the names of our 3 test methods. They are run in parallel.

Info The Test method contains some slow logic that calls Math.Sqrt. When the 3 methods are run, Test() always finishes last.

And This is because the expensive logic in Test() is being run concurrently with the other Test methods.

using System;
using System.Threading.Tasks;

class Program
{
    static void Test()
    {
        // This method always finishes last, because the methods are run in parallel.
        // ... And this one has some computations in it that slow it down.
        for (int i = 0; i < 1000000; i++)
        {
            double value = Math.Sqrt(i);
            if (value == -1)
            {
                return;
            }
        }
        Console.WriteLine("Test");
    }

    static void Test2()
    {
        Console.WriteLine("Test2");
    }

    static void Test3()
    {
        Console.WriteLine("Test3");
    }

    static void Main()
    {
        Parallel.Invoke(Test, Test2, Test3);
    }
}Test2
Test3
Test

Joining

When we call Parallel.Invoke, do all the threads terminate before the following statements are run? This program tests the joining behavior for these parallel threads.

And All the threads created by Parallel.Invoke are joined before the next statement (following Parallel.Invoke) is executed.

using System;
using System.Threading.Tasks;

class Program
{
    static void Test()
    {
        Console.WriteLine("Test");
    }

    static void Test2()
    {
        Console.WriteLine("Test2");
    }

    static void Test3()
    {
        Console.WriteLine("Test3");
    }

    static void Main()
    {
        Parallel.Invoke(Test, Test2, Test3);
        Console.WriteLine("[INTERMEDIATE]");
        Parallel.Invoke(Test, Test2, Test3);
    }
}Test
Test3
Test2
[INTERMEDIATE]
Test
Test3
Test2

Summary

In my experience, Parallel.Invoke is the simplest way to have multithreading in a program. You can run methods on separate processor cores with little additional code.