implab/ImplabNet Commit - r24:ee04e1fa78da

fixed dispatch pool race condition

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Implab.Test/AsyncTests.cs +2 -2

             using System;
             using Microsoft.VisualStudio.TestTools.UnitTesting;
             using System.Reflection;
             using System.Threading;
             using Implab.Parallels;
             namespace Implab.Test {
                 [TestClass]
                 public class AsyncTests {
                     [TestMethod]
                     public void ResolveTest() {
                         int res = -1;
                         var p = new Promise<int>();
                         p.Then(x => res = x);
                         p.Resolve(100);
                         Assert.AreEqual(100, res);
                     }
                     [TestMethod]
                     public void RejectTest() {
                         int res = -1;
                         Exception err = null;
                         var p = new Promise<int>();
                         p.Then(x => res = x, e => err = e);
                         p.Reject(new ApplicationException("error"));
                         Assert.AreEqual(res, -1);
                         Assert.AreEqual(err.Message, "error");
                     }
                     [TestMethod]
                     public void JoinSuccessTest() {
                         var p = new Promise<int>();
                         p.Resolve(100);
                         Assert.AreEqual(p.Join(), 100);
                     }
                     [TestMethod]
                     public void JoinFailTest() {
                         var p = new Promise<int>();
                         p.Reject(new ApplicationException("failed"));
                         try {
                             p.Join();
                             throw new ApplicationException("WRONG!");
                         } catch (TargetInvocationException err) {
                             Assert.AreEqual(err.InnerException.Message, "failed");
                         } catch {
                             Assert.Fail("Got wrong excaption");
                         }
                     }
                     [TestMethod]
                     public void MapTest() {
                         var p = new Promise<int>();
                         var p2 = p.Map(x => x.ToString());
                         p.Resolve(100);
                         Assert.AreEqual(p2.Join(), "100");
                     }
                     [TestMethod]
                     public void FixErrorTest() {
                         var p = new Promise<int>();
                         var p2 = p.Error(e => 101);
                         p.Reject(new Exception());
                         Assert.AreEqual(p2.Join(), 101);
                     }
                     [TestMethod]
                     public void ChainTest() {
                         var p1 = new Promise<int>();
                         var p3 = p1.Chain(x => {
                             var p2 = new Promise<string>();
                             p2.Resolve(x.ToString());
                             return p2;
                         });
                         p1.Resolve(100);
                         Assert.AreEqual(p3.Join(), "100");
                     }
                     [TestMethod]
                     public void PoolTest() {
                         var pid = Thread.CurrentThread.ManagedThreadId;
                         var p = AsyncPool.Invoke(() => Thread.CurrentThread.ManagedThreadId);
                         Assert.AreNotEqual(pid, p.Join());
                     }
                     [TestMethod]
                     public void WorkerPoolSizeTest() {
                         var pool = new WorkerPool(5, 10, 0);
                         Assert.AreEqual(5, pool.PoolSize);
                         pool.Invoke(() => { Thread.Sleep(100000000); return 10; });
                         pool.Invoke(() => { Thread.Sleep(100000000); return 10; });
                         pool.Invoke(() => { Thread.Sleep(100000000); return 10; });
                         Assert.AreEqual(5, pool.PoolSize);
                         for (int i = 0; i < 100; i++)
                             pool.Invoke(() => { Thread.Sleep(100000000); return 10; });
                         Thread.Sleep(200);
                         Assert.AreEqual(10, pool.PoolSize);
                         pool.Dispose();
                     }
                     [TestMethod]
                     public void WorkerPoolCorrectTest() {
                         var pool = new WorkerPool(0,1000,100);
                         int iterations = 1000;
                         int pending = iterations;
                         var stop = new ManualResetEvent(false);
                         var count = 0;
                         for (int i = 0; i < iterations; i++) {
                             pool
                                 .Invoke(() => 1)
                                 .Then(x => Interlocked.Add(ref count, x))
                                 .Then(x => Math.Log10(x))
                                 .Anyway(() => {
                                     Interlocked.Decrement(ref pending);
                                     if (pending == 0)
                                         stop.Set();
                                 });
                         }
                         stop.WaitOne();
                         Assert.AreEqual(iterations, count);
                         Console.WriteLine("Max threads: {0}", pool.MaxRunningThreads);
                         pool.Dispose();
                     }
                     [TestMethod]
                     public void WorkerPoolDisposeTest() {
                         var pool = new WorkerPool(5, 20);
                         Assert.AreEqual(5, pool.PoolSize);
                         pool.Dispose();
                         Thread.Sleep(500);
                         Assert.AreEqual(0, pool.PoolSize);
                         pool.Dispose();
                     }
                     [TestMethod]
                     public void MTQueueTest() {
                         var queue = new MTQueue<int>();
                         int res;
                         queue.Enqueue(10);
                         Assert.IsTrue(queue.TryDequeue(out res));
                         Assert.AreEqual(10, res);
                         Assert.IsFalse(queue.TryDequeue(out res));
                         for (int i = 0; i < 1000; i++)
                             queue.Enqueue(i);
                         for (int i = 0; i < 1000; i++) {
                             queue.TryDequeue(out res);
                             Assert.AreEqual(i, res);
                         }
                         int writers = 0;
                         int readers = 0;
                         var stop = new ManualResetEvent(false);
                         int total = 0;
                         int itemsPerWriter = 1000;
                         int writersCount = 3;
                         for (int i = 0; i < writersCount; i++) {
                             Interlocked.Increment(ref writers);
                             var wn = i;
                             AsyncPool
                                 .InvokeNewThread(() => {
                                     for (int ii = 0; ii < itemsPerWriter; ii++) {
                                         queue.Enqueue(1);
                                     }
                                     return 1;
                                 })
                                 .Anyway(() => Interlocked.Decrement(ref writers));
                         }
                         for (int i = 0; i < 10; i++) {
                             Interlocked.Increment(ref readers);
                             var wn = i;
                             AsyncPool
                                 .InvokeNewThread(() => {
                                     int t;
                                     do {
                                         while (queue.TryDequeue(out t))
                                             Interlocked.Add(ref total, t);
                                     } while (writers > 0);
                                     return 1;
                                 })
                                 .Anyway(() => {
                                     Interlocked.Decrement(ref readers);
                                     if (readers == 0)
                                         stop.Set();
                                 });
                         }
                         stop.WaitOne();
                         Assert.AreEqual(itemsPerWriter * writersCount, total);
                     }
                     [TestMethod]
                     public void ParallelMapTest() {
                         int count = 100000;
                         double[] args = new double[count];
                         var rand = new Random();
                         for (int i = 0; i < count; i++)
                             args[i] = rand.NextDouble();
                         var t = Environment.TickCount;
                         var res = args.ParallelMap(x => Math.Sin(x*x), 4).Join();
                         Console.WriteLine("Map complete in {0} ms", Environment.TickCount - t);
                         t = Environment.TickCount;
                         for (int i = 0; i < count; i++)
                             Assert.AreEqual(Math.Sin(args[i] * args[i]), res[i]);
                         Console.WriteLine("Verified in {0} ms", Environment.TickCount - t);
                     }
                     [TestMethod]
                     public void ChainedMapTest() {
-                        using (var pool = new WorkerPool(4,4,0)) {
+                        using (var pool = new WorkerPool(0,100,0)) {
                             int count = 10000;
                             double[] args = new double[count];
                             var rand = new Random();
                             for (int i = 0; i < count; i++)
                                 args[i] = rand.NextDouble();
                             var t = Environment.TickCount;
                             var res = args
-                                .ChainedMap(
+                                .ChainedMap2(
                                     x => pool.Invoke(
                                         () => Math.Sin(x * x)
                                     ),
                                 )
                                 .Join();
                             Console.WriteLine("Map complete in {0} ms", Environment.TickCount - t);
                             t = Environment.TickCount;
                             for (int i = 0; i < count; i++)
                                 Assert.AreEqual(Math.Sin(args[i] * args[i]), res[i]);
                             Console.WriteLine("Verified in {0} ms", Environment.TickCount - t);
                             Console.WriteLine("Max workers: {0}", pool.MaxRunningThreads);
                         }
                     }
                     [TestMethod]
                     public void ParallelForEachTest() {
                         int count = 100000;
                         int[] args = new int[count];
                         var rand = new Random();
                         for (int i = 0; i < count; i++)
                             args[i] = (int)(rand.NextDouble() * 100);
                         int result = 0;
                         var t = Environment.TickCount;
                         args.ParallelForEach(x => Interlocked.Add(ref result, x), 4).Join();
                         Console.WriteLine("Iteration complete in {0} ms, result: {1}", Environment.TickCount - t, result);
                         int result2 = 0;
                         t = Environment.TickCount;
                         for (int i = 0; i < count; i++)
                             result2 += args[i];
                         Assert.AreEqual(result2, result);
                         Console.WriteLine("Verified in {0} ms", Environment.TickCount - t);
                     }
                     [TestMethod]
                     public void ComplexCase1Test() {
                         var flags = new bool[3];
                         // op1 (aync 200ms) => op2 (async 200ms) => op3 (sync map)
                         var p = PromiseHelper
                             .Sleep(200, "Alan")
                             .Cancelled(() => flags[0] = true)
                             .Chain(x =>
                                 PromiseHelper
                                     .Sleep(200, "Hi, " + x)
                                     .Map(y => y)
                                     .Cancelled(() => flags[1] = true)
                             )
                             .Cancelled(() => flags[2] = true);
                         Thread.Sleep(300);
                         p.Cancel();
                         try {
                             Assert.AreEqual(p.Join(), "Hi, Alan");
                             Assert.Fail("Shouldn't get here");
                         } catch (OperationCanceledException) {
                         }
                         Assert.IsFalse(flags[0]);
                         Assert.IsTrue(flags[1]);
                         Assert.IsTrue(flags[2]);
                     }
                 }
             }

Implab.v11.suo binary modified 0 0

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Implab/Parallels/ArrayTraits.cs +41 0

             using System;
             using System.Collections.Generic;
             using System.Diagnostics;
             using System.Linq;
             using System.Text;
             using System.Threading;
             namespace Implab.Parallels {
                 public static class ArrayTraits {
                     class ArrayIterator<TSrc> : DispatchPool<int> {
                         readonly Action<TSrc> m_action;
                         readonly TSrc[] m_source;
                         readonly Promise<int> m_promise = new Promise<int>();
                         int m_pending;
                         int m_next;
                         public ArrayIterator(TSrc[] source, Action<TSrc> action, int threads)
                             : base(threads) {
                             Debug.Assert(source != null);
                             Debug.Assert(action != null);
                             m_next = 0;
                             m_source = source;
                             m_pending = source.Length;
                             m_action = action;
                             m_promise.Anyway(() => Dispose());
                             m_promise.Cancelled(() => Dispose());
                             InitPool();
                         }
                         public Promise<int> Promise {
                             get {
                                 return m_promise;
                             }
                         }
                         protected override bool TryDequeue(out int unit) {
                             unit = Interlocked.Increment(ref m_next) - 1;
                             return unit >= m_source.Length ? false : true;
                         }
                         protected override void InvokeUnit(int unit) {
                             try {
                                 m_action(m_source[unit]);
                                 var pending = Interlocked.Decrement(ref m_pending);
                                 if (pending == 0)
                                     m_promise.Resolve(m_source.Length);
                             } catch (Exception e) {
                                 m_promise.Reject(e);
                             }
                         }
                     }
                     class ArrayMapper<TSrc, TDst>: DispatchPool<int> {
                         readonly Func<TSrc, TDst> m_transform;
                         readonly TSrc[] m_source;
                         readonly TDst[] m_dest;
                         readonly Promise<TDst[]> m_promise = new Promise<TDst[]>();
                         int m_pending;
                         int m_next;
                         public ArrayMapper(TSrc[] source, Func<TSrc, TDst> transform, int threads)
                             : base(threads) {
                             Debug.Assert (source != null);
                             Debug.Assert( transform != null);
                             m_next = 0;
                             m_source = source;
                             m_dest = new TDst[source.Length];
                             m_pending = source.Length;
                             m_transform = transform;
                             m_promise.Anyway(() => Dispose());
                             m_promise.Cancelled(() => Dispose());
                             InitPool();
                         }
                         public Promise<TDst[]> Promise {
                             get {
                                 return m_promise;
                             }
                         }
                         protected override bool TryDequeue(out int unit) {
                             unit = Interlocked.Increment(ref m_next) - 1;
                             return unit >= m_source.Length ? false : true;
                         }
                         protected override void InvokeUnit(int unit) {
                             try {
                                 m_dest[unit] = m_transform(m_source[unit]);
                                 var pending = Interlocked.Decrement(ref m_pending);
                                 if (pending == 0)
                                     m_promise.Resolve(m_dest);
                             } catch (Exception e) {
                                 m_promise.Reject(e);
                             }
                         }
                     }
                     public static Promise<TDst[]> ParallelMap<TSrc, TDst> (this TSrc[] source, Func<TSrc,TDst> transform, int threads) {
                         if (source == null)
                             throw new ArgumentNullException("source");
                         if (transform == null)
                             throw new ArgumentNullException("transform");
                         var mapper = new ArrayMapper<TSrc, TDst>(source, transform, threads);
                         return mapper.Promise;
                     }
                     public static Promise<int> ParallelForEach<TSrc>(this TSrc[] source, Action<TSrc> action, int threads) {
                         if (source == null)
                             throw new ArgumentNullException("source");
                         if (action == null)
                             throw new ArgumentNullException("action");
                         var iter = new ArrayIterator<TSrc>(source, action, threads);
                         return iter.Promise;
                     }
                     public static Promise<TDst[]> ChainedMap<TSrc, TDst>(this TSrc[] source, ChainedOperation<TSrc, TDst> transform, int threads) {
                         if (source == null)
                             throw new ArgumentNullException("source");
                         if (transform == null)
                             throw new ArgumentNullException("transform");
                         if (threads <= 0)
                             throw new ArgumentOutOfRangeException("Threads number must be greater then zero");
                         var promise = new Promise<TDst[]>();
                         var res = new TDst[source.Length];
                         var pending = source.Length;
                         var semaphore = new Semaphore(threads, threads);
                         AsyncPool.InvokeNewThread(() => {
                             for (int i = 0; i < source.Length; i++) {
                                 if(promise.IsResolved)
                                     break; // stop processing in case of error or cancellation
                                 var idx = i;
                                 semaphore.WaitOne();
                                 try {
                                     var p1 = transform(source[i]);
                                     p1.Anyway(() => semaphore.Release());
                                     p1.Cancelled(() => semaphore.Release());
                                     p1.Then(
                                         x => {
                                             res[idx] = x;
                                             var left = Interlocked.Decrement(ref pending);
                                             if (left == 0)
                                                 promise.Resolve(res);
                                         },
                                         e => promise.Reject(e)
                                     );
                                 } catch (Exception e) {
                                     promise.Reject(e);
                                 }
                             }
                             return 0;
                         });
                         return promise.Anyway(() => semaphore.Dispose());
                     }
+                    /*
+                    this method is pretty fast, but it may cause a stack overflow if an element transformation is made faster then the next operation is
+                    be chained, in this case the syncronous callback invocation will occur
+                    public static Promise<TDst[]> ChainedMap2<TSrc, TDst>(this TSrc[] source, ChainedOperation<TSrc, TDst> transform, int threads) {
+                        if (source == null)
+                            throw new ArgumentNullException("source");
+                        if (transform == null)
+                            throw new ArgumentNullException("transform");
+                        if (threads <= 0)
+                            throw new ArgumentOutOfRangeException("Threads number must be greater then zero");
+                        var promise = new Promise<TDst[]>();
+                        var res = new TDst[source.Length];
+                        var index = -1; // we will start with increment
+                        var len = source.Length;
+                        var pending = len;
+                        Action<int> callback = null;
+                        callback = (current) => {
+                            if (current < len) {
+                                transform(source[current])
+                                    .Then(
+                                        x => {
+                                            res[current] = x;
+                                            if (Interlocked.Decrement(ref pending) == 0)
+                                                promise.Resolve(res);
+                                            else
+                                                callback(Interlocked.Increment(ref index));
+                                        },
+                                        e => promise.Reject(e)
+                                    );
+                            }
+                        };
+                        for (int i = 0; i < threads; i++)
+                            callback(Interlocked.Increment(ref index));
+                        return promise;
+                    }
+                     */
                 }
             }

Implab/Parallels/DispatchPool.cs +4 -2

             using System;
             using System.Collections.Generic;
             using System.Linq;
             using System.Text;
             using System.Threading;
             using System.Diagnostics;
             namespace Implab.Parallels {
                 public abstract class DispatchPool<TUnit> : IDisposable {
                     readonly int m_minThreads;
                     readonly int m_maxThreads;
                     int m_createdThreads = 0; // the current size of the pool
                     int m_activeThreads = 0; // the count of threads which are active
                     int m_sleepingThreads = 0; // the count of currently inactive threads
                     int m_maxRunningThreads = 0; // the meximum reached size of the pool
                     int m_exitRequired = 0; // the pool is going to shutdown, all unused workers are released
                     int m_releaseTimeout = 100; // the timeout while the working thread will wait for the new tasks before exit
                     int m_wakeEvents = 0; // the count of wake events
                     AutoResetEvent m_hasTasks = new AutoResetEvent(false);
                     protected DispatchPool(int min, int max) {
                         if (min < 0)
                             throw new ArgumentOutOfRangeException("min");
                         if (max <= 0)
                             throw new ArgumentOutOfRangeException("max");
                         if (min > max)
                             min = max;
                         m_minThreads = min;
                         m_maxThreads = max;
                     }
                     protected DispatchPool(int threads)
                         : this(threads, threads) {
                     }
                     protected DispatchPool() {
                         int maxThreads, maxCP;
                         ThreadPool.GetMaxThreads(out maxThreads, out maxCP);
                         m_minThreads = 0;
                         m_maxThreads = maxThreads;
                     }
                     protected void InitPool() {
                         for (int i = 0; i < m_minThreads; i++)
                             StartWorker();
                     }
                     public int PoolSize {
                         get {
                             return m_createdThreads;
                         }
                     }
                     public int ActiveThreads {
                         get {
                             return m_activeThreads;
                         }
                     }
                     public int MaxRunningThreads {
                         get {
                             return m_maxRunningThreads;
                         }
                     }
                     protected bool IsDisposed {
                         get {
                             return m_exitRequired != 0;
                         }
                     }
                     protected abstract bool TryDequeue(out TUnit unit);
                     #region thread execution traits
                     int SignalThread() {
                         var signals = Interlocked.Increment(ref m_wakeEvents);
                         if(signals == 1)
                             m_hasTasks.Set();
                         return signals;
                     }
                     bool FetchSignalOrWait(int timeout) {
                         var start = Environment.TickCount;
                         // означает, что поток владеет блокировкой и при успешном получении сигнала должен
                         // ее вернуть, чтобы другой ожидающий поток смог
                         bool hasLock = false;
                         do {
                             int signals;
                             do {
                                 signals = m_wakeEvents;
                                 if (signals == 0)
                                     break;
                             } while (Interlocked.CompareExchange(ref m_wakeEvents, signals - 1, signals) != signals);
                             if (signals >= 1) {
                                 if (signals > 1 && hasLock)
                                     m_hasTasks.Set();
                                 return true;
                             }
                             if (timeout != -1)
                                 timeout = Math.Max(0, timeout - (Environment.TickCount - start));
                             // если сигналов больше не осталось, то первый поток, который дошел сюда сбросит событие
                             // и уйдет на пустой цикл, после чего заблокируется
                             hasLock = true;
                         } while (m_hasTasks.WaitOne(timeout));
                         return false;
                     }
                     bool Sleep(int timeout) {
                         Interlocked.Increment(ref m_sleepingThreads);
                         if (FetchSignalOrWait(timeout)) {
                             Interlocked.Decrement(ref m_sleepingThreads);
                             return true;
                         } else {
                             Interlocked.Decrement(ref m_sleepingThreads);
                             return false;
                         }
                     }
                     #endregion
                     /// <summary>
                     /// Запускает либо новый поток, если раньше не было ни одного потока, либо устанавливает событие пробуждение одного спящего потока
                     /// </summary>
                     protected void GrowPool() {
                         if (m_exitRequired != 0)
                             return;
                         if (m_sleepingThreads > m_wakeEvents) {
                             //Console.WriteLine("Waking threads (sleeps {0}, pending {1})", m_sleepingThreads, m_wakeEvents);
                             // all sleeping threads may gone
                             SignalThread(); // wake a sleeping thread;
                             // we can't check whether signal has been processed
                             // anyway it may take some time for the thread to start
                             // we will ensure that at least one thread is running
                             if (AllocateThreadSlot(1)) {
                                 // if there were no threads in the pool
                                 var worker = new Thread(this.Worker);
                                 worker.IsBackground = true;
                                 worker.Start();
                             }
                         } else {
                             // if there is no sleeping threads in the pool
-                            StartWorker();
+                            if (!StartWorker())
+                                // we haven't started a new thread, but the current can be on the way and it can't process the queue
+                                // send it a signal to spin again
+                                SignalThread();
                         }
                     }
                     private bool Suspend() {
                         //no tasks left, exit if the thread is no longer needed
                         bool last;
                         bool requestExit;
                         // if threads have a timeout before releasing
                         if (m_releaseTimeout > 0)
                             requestExit = !Sleep(m_releaseTimeout);
                         else
                             requestExit = true;
                         if (!requestExit)
                             return true;
                         // release unsused thread
                         if (requestExit && ReleaseThreadSlot(out last)) {
                             // in case at the moment the last thread was being released
                             // a new task was added to the queue, we need to try
                             // to revoke the thread to avoid the situation when the task is left unprocessed
                             if (last && Sleep(0)) { // Sleep(0) will fetch pending task or will return false
                                 if (AllocateThreadSlot(1))
                                     return true; // spin again...
                                 else
                                     SignalThread(); // since Sleep(0) has fetched the signal we neet to reschedule it
                             }
                             return false;
                         }
                         // wait till infinity
                         Sleep(-1);
                         return true;
                     }
                     #region thread slots traits
                     bool AllocateThreadSlot() {
                         int current;
                         // use spins to allocate slot for the new thread
                         do {
                             current = m_createdThreads;
                             if (current >= m_maxThreads || m_exitRequired != 0)
                                 // no more slots left or the pool has been disposed
                                 return false;
                         } while (current != Interlocked.CompareExchange(ref m_createdThreads, current + 1, current));
                         UpdateMaxThreads(current + 1);
                         return true;
                     }
                     bool AllocateThreadSlot(int desired) {
                         if (desired - 1 != Interlocked.CompareExchange(ref m_createdThreads, desired, desired - 1))
                             return false;
                         UpdateMaxThreads(desired);
                         return true;
                     }
                     bool ReleaseThreadSlot(out bool last) {
                         last = false;
                         int current;
                         // use spins to release slot for the new thread
                         do {
                             current = m_createdThreads;
                             if (current <= m_minThreads && m_exitRequired == 0)
                                 // the thread is reserved
                                 return false;
                         } while (current != Interlocked.CompareExchange(ref m_createdThreads, current - 1, current));
                         last = (current == 1);
                         return true;
                     }
                     /// <summary>
                     /// releases thread slot unconditionally, used during cleanup
                     /// </summary>
                     /// <returns>true - no more threads left</returns>
                     bool ReleaseThreadSlotAnyway() {
                         var left = Interlocked.Decrement(ref m_createdThreads);
                         return left == 0;
                     }
                     void UpdateMaxThreads(int count) {
                         int max;
                         do {
                             max = m_maxRunningThreads;
                             if (max >= count)
                                 break;
                         } while(max != Interlocked.CompareExchange(ref m_maxRunningThreads, count, max));
                     }
                     #endregion
                     bool StartWorker() {
                         if (AllocateThreadSlot()) {
                             // slot successfully allocated
                             var worker = new Thread(this.Worker);
                             worker.IsBackground = true;
                             worker.Start();
                             return true;
                         } else {
                             return false;
                         }
                     }
                     protected abstract void InvokeUnit(TUnit unit);
                     void Worker() {
                         TUnit unit;
                         //Console.WriteLine("{0}: Active", Thread.CurrentThread.ManagedThreadId);
                         Interlocked.Increment(ref m_activeThreads);
                         do {
                             // exit if requested
                             if (m_exitRequired != 0) {
                                 // release the thread slot
                                 Interlocked.Decrement(ref m_activeThreads);
                                 if (ReleaseThreadSlotAnyway()) // it was the last worker
                                     m_hasTasks.Dispose();
                                 else
                                     SignalThread(); // wake next worker
-                                unit = default(TUnit);
                                 break;
                             }
                             // fetch task
                             if (TryDequeue(out unit)) {
                                 InvokeUnit(unit);
                                 continue;
                             }
                             Interlocked.Decrement(ref m_activeThreads);
                             // entering suspend state
                             // keep this thread and wait
                             if (!Suspend())
                                 break;
                             //Console.WriteLine("{0}: Awake", Thread.CurrentThread.ManagedThreadId);
                             Interlocked.Increment(ref m_activeThreads);
                         } while (true);
                         //Console.WriteLine("{0}: Exited", Thread.CurrentThread.ManagedThreadId);
                     }
                     protected virtual void Dispose(bool disposing) {
                         if (disposing) {
                             if (m_exitRequired == 0) {
                                 if (Interlocked.CompareExchange(ref m_exitRequired, 1, 0) != 0)
                                     return;
                                 // wake sleeping threads
                                 if (m_createdThreads > 0)
                                     SignalThread();
                                 else
                                     m_hasTasks.Dispose();
                                 GC.SuppressFinalize(this);
                             }
                         }
                     }
                     public void Dispose() {
                         Dispose(true);
                     }
                     ~DispatchPool() {
                         Dispose(false);
                     }
                 }
             }

Implab/Parallels/MTQueue.cs +1 -1

             using System;
             using System.Collections.Generic;
             using System.Linq;
             using System.Text;
             using System.Threading;
             namespace Implab.Parallels {
                 public class MTQueue<T> {
                     class Node {
                         public Node(T value) {
                             this.value = value;
                         }
                         public readonly T value;
                         public Node next;
                     }
                     Node m_first;
                     Node m_last;
                     public void Enqueue(T value) {
                         var last = m_last;
                         var next = new Node(value);
                         while (last != Interlocked.CompareExchange(ref m_last, next, last))
                             last = m_last;
                         if (last != null)
                             last.next = next;
                         else
                             m_first = next;
                     }
                     public bool TryDequeue(out T value) {
                         Node first;
                         Node next = null;
                         value = default(T);
                         do {
                             first = m_first;
                             if (first == null)
                                 return false;
                             next = first.next;
                             if (next == null) {
                                 // this is the last element,
                                 // then try to update the tail
                                 if (first != Interlocked.CompareExchange(ref m_last, null, first)) {
-                                    // this is a ace condition
+                                    // this is a race condition
                                     if (m_last == null)
                                         // the queue is empty
                                         return false;
                                     // tail has been changed, than we need to restart
                                     continue;
                                 }
                                 // tail succesfully updated and first.next will never be changed
                                 // other readers will fail due to inconsistency m_last != m_fist, but m_first.next == null
                                 // but the writer may update the m_first since the m_last is null
                                 // so we need to fix inconsistency by setting m_first to null, but if it already has been
                                 // updated by a writer then we should just give up
                                 Interlocked.CompareExchange(ref m_first, null, first);
                                 break;
                             } else {
                                     if (first == Interlocked.CompareExchange(ref m_first, next, first))
                                         // head succesfully updated
                                         break;
                             }
                         } while (true);
                         value = first.value;
                         return true;
                     }
                 }
             }

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