--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/Parallels/DispatchPool.cs	Thu Nov 07 03:41:32 2013 +0400
@@ -0,0 +1,171 @@
+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_runningThreads = 0;
+        int m_maxRunningThreads = 0;
+        int m_suspended = 0;
+        int m_exitRequired = 0;
+        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 ThreadCount {
+            get {
+                return m_runningThreads;
+            }
+        }
+
+        public int MaxRunningThreads {
+            get {
+                return m_maxRunningThreads;
+            }
+        }
+
+        protected bool IsDisposed {
+            get {
+                return m_exitRequired != 0;
+            }
+        }
+
+        bool StartWorker() {
+            var current = m_runningThreads;
+            // use spins to allocate slot for the new thread
+            do {
+                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_runningThreads, current + 1, current));
+
+            m_maxRunningThreads = Math.Max(m_maxRunningThreads, current + 1);
+
+            // slot successfully allocated
+
+            var worker = new Thread(this.Worker);
+            worker.IsBackground = true;
+            worker.Start();
+
+            return true;
+        }
+
+        protected abstract bool TryDequeue(out TUnit unit);
+
+        protected virtual void WakeNewWorker() {
+            if (m_suspended > 0)
+                m_hasTasks.Set();
+            else
+                StartWorker();
+        }
+
+        bool FetchTask(out TUnit unit) {
+            do {
+                // exit if requested
+                if (m_exitRequired != 0) {
+                    // release the thread slot
+                    int running;
+                    do {
+                        running = m_runningThreads;
+                    } while (running != Interlocked.CompareExchange(ref m_runningThreads, running - 1, running));
+                    running--;
+
+                    if (running == 0) // it was the last worker
+                        m_hasTasks.Dispose();
+                    else
+                        m_hasTasks.Set(); // release next worker
+                    unit = default(TUnit);
+                    return false;
+                }
+
+                // fetch task
+                if (TryDequeue(out unit)) {
+                    WakeNewWorker();
+                    return true;
+                }
+
+                //no tasks left, exit if the thread is no longer needed
+                int runningThreads;
+                bool exit = true;
+                do {
+                    runningThreads = m_runningThreads;
+                    if (runningThreads <= m_minThreads) {
+                        exit = false;
+                        break;
+                    }
+                } while (runningThreads != Interlocked.CompareExchange(ref m_runningThreads, runningThreads - 1, runningThreads));
+
+                if (exit) {
+                    Interlocked.Decrement(ref m_runningThreads);
+                    return false;
+                }
+
+                // keep this thread and wait
+                Interlocked.Increment(ref m_suspended);
+                m_hasTasks.WaitOne();
+                Interlocked.Decrement(ref m_suspended);
+            } while (true);
+        }
+
+        protected abstract void InvokeUnit(TUnit unit);
+
+        void Worker() {
+            TUnit unit;
+            while (FetchTask(out unit))
+                InvokeUnit(unit);
+        }
+
+        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
+                    m_hasTasks.Set();
+                    GC.SuppressFinalize(this);
+                }
+            }
+        }
+
+        public void Dispose() {
+            Dispose(true);
+        }
+
+        ~DispatchPool() {
+            Dispose(false);
+        }
+    }
+}