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Multithreading Help

Posted by Programmer16, 29 November 2011 · 205 views

I have never ventured in to the land of multithreading very far; only a thread here and there when I really needed it. I honestly have never really had a need for it; my projects never really get far enough to require them. I do, however, have a couple projects that would have probably benefited from it, so I am working on getting at least some support for it in the next version of my code base.

I've started with the simplest form I could think of: my task system. It is a very simple system: I create a Task class, instantiate it, add it to the manager and the manager updates it every tick until it is finished. For the test, I created a very basic base class, AsyncTask, which handles the initialization and such. I then implemented a LoadTextFileTask and AsyncLoadTextTask, both of which do the same job (streaming all of the data in the file into memory.)

The problem is, I have no clue if I'm even really doing this properly or if I'm way off the mark. So, if anyone is willing to take a gander, I'd greatly appreciate any input. Here is the AsyncTask:

public class AsyncTask : Dubnium2D.Core.Task

{

    private object lockObject = new object();

    protected Thread thread = null;



    protected bool CrossThreadCheck

    {

        get

        {

            lock(lockObject)

            {

                return Thread.CurrentThread != thread;

            }

        }

    }



    public AsyncTask(bool DelayStart = false)

    {

        thread = new Thread(() =>

        {

            Utilities.Timing.ProfileTimer Timer = new Utilities.Timing.ProfileTimer();

            while(true)

            {

                Timer.Update();

                lock(lockObject)

                {

                    if(this.IsDead)

                        break;



                    if(this.IsPaused)

                        continue;

                }



                this.Update(Timer.Delta);

            }

            Kill();

        });



        if(!DelayStart)

            thread.Start();

    }



    public override void Update(float Delta)

    {

        if(CrossThreadCheck)

        {

            if(IsDead || IsPaused || thread.ThreadState != ThreadState.Running)

                return;



            if(thread.ThreadState == ThreadState.Unstarted)

                thread.Start();

            return;

        }

        base.Update(Delta);

    }

}



And here is the AsyncLoadTextTask class:

public sealed class AsyncLoadTextTask : AsyncTask

{

    private object lockObject = new object();



    private System.IO.StreamReader reader = null;

    private char[] data = null;

    private int currentIndex = 0;

    private int bufferSize = 0;

    private int length = 0;

    private string filePath = string.Empty;

    private int progress = 0;



    private int charactersRemaining

    {

        get

        {

            lock(lockObject)

            {

                return length - currentIndex;

            }

        }

    }



    /// <summary>

    /// Gets the path to the file that is being loaded.

    /// </summary>

    public string FilePath

    {

        get

        {

            lock(lockObject)

            {

                return filePath;

            }

        }

        private set

        {

            lock(lockObject)

            {

                filePath = value;

            }

        }

    }



    /// <summary>

    /// Gets the data that was loaded from the file. Will throw an exception if the loading process is not finished.

    /// </summary>

    public string Data

    {

        get

        {

            lock(lockObject)

            {

                if(!IsDead)

                    throw new InvalidOperationException();

                return new string(data);

            }

        }

    }



    /// <summary>

    /// Gets the progress of the load process.

    /// </summary>

    public int Progress

    {

        get

        {

            lock(lockObject)

            {

                return progress;

            }

        }

        private set

        {

            lock(lockObject)

            {

                progress = value;

            }

        }

    }



    /// <summary>

    /// Initializes a new instance of the <see cref="AsyncLoadTextTask"/> class.

    /// </summary>

    /// <param name="FilePath">The path to the file to load into memory.</param>

    /// <param name="BufferSize">Size of the buffer to use when loading the data.</param>

    public AsyncLoadTextTask(string FilePath, int BufferSize)

    {

        this.FilePath = FilePath;

        reader = new System.IO.StreamReader(FilePath);

        this.length = (int)reader.BaseStream.Length;

        this.data = new char[length];

        this.bufferSize = BufferSize;

    }



    /// <summary>

    /// Updates the task using the supplied time delta.

    /// If the task was created with DelayStart = true, then calling this from outside of the task's thread will start it. Otherwise, calling it from outside of the task's thread will do nothing.

    /// </summary>

    /// <param name="Delta">The time, in seconds, since the last update.</param>

    public override void Update(float Delta)

    {

        base.Update(Delta);

        if(CrossThreadCheck)

            return;



        lock(lockObject)

        {

            int BytesRead = reader.Read(data, currentIndex, Math.Min(charactersRemaining, bufferSize));

            currentIndex += BytesRead;



            this.Progress = (int)(100.0f * ((float)currentIndex / (float)length));



            if(currentIndex >= length)

            {

                this.reader.Close();

                this.reader.Dispose();

                Kill();

            }

        }

    }

}



Again, any input will be greatly appreciated.




I understand you're trying to learn how this stuff works, but, .net already has this functionality built in. I'd suggest you look at the System.Threading.Tasks namespace, and at least study their interface before you roll your own. http://msdn.microsoft.com/en-us/library/ff963549.aspx
Thanks Deyja, I didn't realize that namespace was even there; I'll check it out.

I don't plan on using this class for anything as it defeats the purpose of my task system; I lose all control over the flow of the tasks. I just chose it as it was the first thing that came to mind.

Thanks again for the link to the article!
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