Understanding multithreading

Multithreading is a prevalent programming and execution model that enables the concurrent existence of multiple threads within a single process. While these threads share the process’s resources, they can execute independently. In contrast, single-threading processes one command at a time.

The primary aim of multithreading is to enable computers to perform more than one task simultaneously. While it may not significantly enhance overall speed on a single-core computer, it proves advantageous on systems with multiple processor cores. In such cases, multithreading leverages additional cores to execute separate instructions simultaneously or distribute tasks among the cores.

Multithreading in .NET

In the context of .NET, there are several methods for implementing multithreading, including:

Thread class	Responsible for creating and manipulating threads in Windows.
ThreadPool class	Manages a group of threads, automatically starting tasks when threads are created.
Task class	Represents asynchronous operations and is part of the Task Parallel Library for running tasks asynchronously and in parallel.
BackgroundWorker class	Executes operations on a separate thread.

Code examples and performance metrics

Thread class:

Thread[] t = new Thread[threadCount];
for (int i = 0; i < threadCount; i++)
{
    t[i] = new Thread(() =>
    {
        DoComplexWork();
    });
    t[i].Priority = ThreadPriority.Highest;
    t[i].Start();
}
foreach (var ct in t)
{
    ct.Join();
}

ThreadPool class:

using (CountdownEvent signaler = new CountdownEvent(threadCount))
{
    for (int i = 0; i < threadCount; i++)
    {
        ThreadPool.QueueUserWorkItem((x) =>
        {
            DoComplexWork();
            signaler.Signal();
        });
    }
    signaler.Wait();
}

Task class:

Task[] taskList = new Task[threadCount];
for (int i = 0; i < threadCount; i++)
{
    taskList[i] = new Task(new Action(() =>
    {
        DoComplexWork();
    }));
    taskList[i].Start();
}
Task.WaitAll(taskList);

BackgroundWorker class:

BackgroundWorker[] backgroundWorkerList = new BackgroundWorker[threadCount];
using (CountdownEvent signaler = new CountdownEvent(threadCount))
{
    for (int i = 0; i < threadCount; i++)
    {
        backgroundWorkerList[i] = new BackgroundWorker();
        backgroundWorkerList[i].DoWork += delegate (object sender, DoWorkEventArgs e)
        {
            DoComplexWork();
            signaler.Signal();
        };
        backgroundWorkerList[i].RunWorkerAsync();
    }
    signaler.Wait();
}

Benchmark summary

Single threading	8419ms
Multithreading using Thread	7532ms
Multithreading using ThreadPool	2901ms
Multithreading using Task	3061ms
Multithreading using BackgroundWorker	3100ms

In summary, when compared to single threading and the Thread class, ThreadPool, Task, and BackgroundWorker demonstrate approximately 2x faster performance. Therefore, incorporating multithreading techniques in CPU-intensive tasks can significantly enhance application performance. Among these, the BackgroundWorker class stands out as both user-friendly and popular among developers.