Question

I’ve created a custom thread pool utility, but there seems to be a problem that I cannot find.

using System; using System.Collections; using System.Collections.Generic; using System.Threading;  namespace iWallpaper.S3Uploader { public class QueueManager<T> {     private readonly Queue queue = Queue.Synchronized(new Queue());     private readonly AutoResetEvent res = new AutoResetEvent(true);     private readonly AutoResetEvent res_thr = new AutoResetEvent(true);     private readonly Semaphore sem = new Semaphore(1, 4);     private readonly Thread thread;     private Action<T> DoWork;     private int Num_Of_Threads;      private QueueManager()     {         Num_Of_Threads = 0;         maxThread = 5;         thread = new Thread(Worker) {Name = 'S3Uploader EventRegisterer'};         thread.Start();          //   log.Info(String.Format('{0} [QUEUE] FileUploadQueueManager created', DateTime.Now.ToLongTimeString()));     }      public int maxThread { get; set; }      public static FileUploadQueueManager<T> Instance     {         get { return Nested.instance; }     }      /// <summary>     /// Executes multythreaded operation under items     /// </summary>     /// <param name='list'>List of items to proceed</param>     /// <param name='action'>Action under item</param>     /// <param name='MaxThreads'>Maximum threads</param>     public void Execute(IEnumerable<T> list, Action<T> action, int MaxThreads)     {         maxThread = MaxThreads;         DoWork = action;         foreach (T item in list)         {             Add(item);         }     }     public void ExecuteNoThread(IEnumerable<T> list, Action<T> action)     {         ExecuteNoThread(list, action, 0);     }     public void ExecuteNoThread(IEnumerable<T> list, Action<T> action, int MaxThreads)     {         foreach (T wallpaper in list)         {             action(wallpaper);         }     }     /// <summary>     /// Default 10 threads     /// </summary>     /// <param name='list'></param>     /// <param name='action'></param>     public void Execute(IEnumerable<T> list, Action<T> action)     {         Execute(list, action, 10);     }      private void Add(T item)     {         lock (queue)         {             queue.Enqueue(item);         }         res.Set();     }      private void Worker()     {         while (true)         {             if (queue.Count == 0)             {                 res.WaitOne();             }              if (Num_Of_Threads < maxThread)             {                 var t = new Thread(Proceed);                 t.Start();             }             else             {                 res_thr.WaitOne();             }         }     }      private void Proceed()     {         Interlocked.Increment(ref Num_Of_Threads);         if (queue.Count > 0)         {             var item = (T) queue.Dequeue();              sem.WaitOne();             ProceedItem(item);             sem.Release();         }         res_thr.Set();         Interlocked.Decrement(ref Num_Of_Threads);     }      private void ProceedItem(T activity)     {         if (DoWork != null)             DoWork(activity);          lock (Instance)         {             Console.Title = string.Format('ThrId:{0}/{4}, {1}, Activity({2} left):{3}',                                           thread.ManagedThreadId, DateTime.Now, queue.Count, activity,                                           Num_Of_Threads);         }     }      #region Nested type: Nested      protected class Nested     {         // Explicit static constructor to tell C# compiler         // not to mark type as beforefieldinit         internal static readonly QueueManager<T> instance = new FileUploadQueueManager<T>();     }      #endregion  } 

}

Problem is here:

Console.Title = string.Format('ThrId:{0}/{4}, {1}, Activity({2} left):{3}',                                       thread.ManagedThreadId, DateTime.Now, queue.Count, activity,                                       Num_Of_Threads); 

There is always ONE thread id in title. And program seems to be working in one thread.

Sample usage:

        var i_list = new int[] {1, 2, 4, 5, 6, 7, 8, 6};         QueueManager<int>.Instance.Execute(i_list,           i =>           {               Console.WriteLine('Some action under element number {0}', i);            }, 5); 

P.S.: it’s pretty messy, but I’m still working on it.

Answer 1

Writing robust threaded code is not trivial. There are numerous thread-pools around that you might look at for reference, but also note that Parallel Extensions (available as CTP, or later in .NET 4.0) includes a lot of additional threading constructs out-of-the-box (in the TPL/CCR). For example, Parallel.For / Parallel.ForEach, which deal with work-stealing, and handling the available cores effectively.

For an example of a pre-rolled thread-pool, see Jon Skeet’s CustomThreadPool here.