diff --git a/Implab.Test/AsyncTests.cs b/Implab.Test/AsyncTests.cs
--- a/Implab.Test/AsyncTests.cs
+++ b/Implab.Test/AsyncTests.cs
@@ -99,7 +99,7 @@ namespace Implab.Test {
 
         [TestMethod]
         public void WorkerPoolSizeTest() {
-            var pool = new WorkerPool(5, 10);
+            var pool = new WorkerPool(5, 10, 0);
 
             Assert.AreEqual(5, pool.ThreadCount);
 
@@ -119,7 +119,7 @@ namespace Implab.Test {
 
         [TestMethod]
         public void WorkerPoolCorrectTest() {
-            var pool = new WorkerPool();
+            var pool = new WorkerPool(0,1000,100);
 
             int iterations = 1000;
             int pending = iterations;
@@ -244,7 +244,7 @@ namespace Implab.Test {
         [TestMethod]
         public void ChainedMapTest() {
 
-            using (var pool = new WorkerPool(1,10)) {
+            using (var pool = new WorkerPool(8,100,0)) {
                 int count = 10000;
 
                 double[] args = new double[count];
diff --git a/Implab.v11.suo b/Implab.v11.suo
index d05880eb554a9716b818e81f9e8e949a3388219a..0324d71b1911ff2672c0c8ae7c7d19bceabeae2e
GIT binary patch
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diff --git a/Implab/Parallels/DispatchPool.cs b/Implab/Parallels/DispatchPool.cs
--- a/Implab/Parallels/DispatchPool.cs
+++ b/Implab/Parallels/DispatchPool.cs
@@ -62,7 +62,36 @@ namespace Implab.Parallels {
             }
         }
 
-        bool StartWorker() {
+        protected abstract bool TryDequeue(out TUnit unit);
+
+        protected virtual bool ExtendPool() {
+            if (m_suspended > 0) {
+                m_hasTasks.Set();
+                return true;
+            } else
+                return StartWorker();
+        }
+
+        /// <summary>
+        /// Запускает либо новый поток, если раньше не было ни одного потока, либо устанавливает событие пробуждение одного спящего потока
+        /// </summary>
+        protected void WakePool() {
+            m_hasTasks.Set(); // wake sleeping thread;
+
+            if (AllocateThreadSlot(1)) {
+                var worker = new Thread(this.Worker);
+                worker.IsBackground = true;
+                worker.Start();
+            }
+        }
+
+        protected virtual void Suspend() {
+            m_hasTasks.WaitOne();
+        }
+
+        #region thread slots traits
+
+        bool AllocateThreadSlot() {
             int current;
             // use spins to allocate slot for the new thread
             do {
@@ -72,38 +101,67 @@ namespace Implab.Parallels {
                     return false;
             } while (current != Interlocked.CompareExchange(ref m_runningThreads, current + 1, current));
 
-            m_maxRunningThreads = Math.Max(m_maxRunningThreads, current + 1);
+            UpdateMaxThreads(current + 1);
+
+            return true;
+        }
 
-            // slot successfully allocated
+        bool AllocateThreadSlot(int desired) {
+            if (desired - 1 != Interlocked.CompareExchange(ref m_runningThreads, desired, desired - 1))
+                return false;
+
+            UpdateMaxThreads(desired);
 
-            var worker = new Thread(this.Worker);
-            worker.IsBackground = true;
-            worker.Start();
+            return true;
+        }
+
+        bool ReleaseThreadSlot(out bool last) {
+            last = false;
+            int current;
+            // use spins to release slot for the new thread
+            do {
+                current = m_runningThreads;
+                if (current <= m_minThreads && m_exitRequired == 0)
+                    // the thread is reserved
+                    return false;
+            } while (current != Interlocked.CompareExchange(ref m_runningThreads, current - 1, current));
+
+            last = (current == 1);
 
             return true;
         }
 
-        protected abstract bool TryDequeue(out TUnit unit);
-
-        protected virtual void WakeNewWorker(bool extend) {
-            if (m_suspended > 0)
-                m_hasTasks.Set();
-            else
-                StartWorker();
+        /// <summary>
+        /// releases thread slot unconditionally, used during cleanup
+        /// </summary>
+        /// <returns>true - no more threads left</returns>
+        bool ReleaseThreadSlotAnyway() {
+            var left = Interlocked.Decrement(ref m_runningThreads);
+            return left == 0;
         }
 
-        /// <summary>
-        /// Запускает либо новый поток, если раньше не было ни одного потока, либо устанавливает событие пробуждение одного спящего потока
-        /// </summary>
-        protected void StartIfIdle() {
-            int threads;
+        void UpdateMaxThreads(int count) {
+            int max;
             do {
-
-            }
+                max = m_maxRunningThreads;
+                if (max >= count)
+                    break;
+            } while(max != Interlocked.CompareExchange(ref m_maxRunningThreads, count, max));
         }
 
-        protected virtual void Suspend() {
-            m_hasTasks.WaitOne();
+        #endregion
+
+        bool StartWorker() {
+            if (AllocateThreadSlot()) {
+                // slot successfully allocated
+                var worker = new Thread(this.Worker);
+                worker.IsBackground = true;
+                worker.Start();
+
+                return true;
+            } else {
+                return false;
+            }
         }
 
         bool FetchTask(out TUnit unit) {
@@ -111,35 +169,32 @@ namespace Implab.Parallels {
                 // exit if requested
                 if (m_exitRequired != 0) {
                     // release the thread slot
-                    var running = Interlocked.Decrement(ref m_runningThreads);
-                    if (running == 0) // it was the last worker
+                    if (ReleaseThreadSlotAnyway()) // it was the last worker
                         m_hasTasks.Dispose();
                     else
-                        m_hasTasks.Set(); // release next worker
+                        m_hasTasks.Set(); // wake next worker
                     unit = default(TUnit);
                     return false;
                 }
 
                 // fetch task
                 if (TryDequeue(out unit)) {
-                    WakeNewWorker(true);
+                    ExtendPool();
                     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) {
-                        // check wheather this is the last thread and we have tasks
+                bool last;
+                if (ReleaseThreadSlot(out last)) {
+                    if (last && m_hasTasks.WaitOne(0)) {
+                        if (AllocateThreadSlot(1))
+                            continue; // spin again...
+                        else
+                            // we failed to reallocate slot for this thread
+                            // therefore we need to release the event
+                            m_hasTasks.Set(); 
+                    }
 
-                        exit = false;
-                        break;
-                    }
-                } while (runningThreads != Interlocked.CompareExchange(ref m_runningThreads, runningThreads - 1, runningThreads));
-
-                if (exit) {
                     return false;
                 }
 
diff --git a/Implab/Parallels/WorkerPool.cs b/Implab/Parallels/WorkerPool.cs
--- a/Implab/Parallels/WorkerPool.cs
+++ b/Implab/Parallels/WorkerPool.cs
@@ -57,17 +57,16 @@ namespace Implab.Parallels {
             var len = Interlocked.Increment(ref m_queueLength);
             m_queue.Enqueue(unit);
 
-            if (ThreadCount == 0)
-                // force to start
-                WakeNewWorker(false);
+            if(!ExtendPool())
+                WakePool();
         }
 
-        protected override void WakeNewWorker(bool extend) {
-            if (extend && m_queueLength <= m_threshold)
+        protected override bool ExtendPool() {
+            if (m_queueLength <= m_threshold*ThreadCount)
                 // in this case we are in active thread and it request for additional workers
                 // satisfy it only when queue is longer than threshold
-                return;
-            base.WakeNewWorker(extend);
+                return false;
+            return base.ExtendPool();
         }
 
         protected override bool TryDequeue(out Action unit) {