diff --git a/Implab/Parallels/BlockingQueue.cs b/Implab/Parallels/BlockingQueue.cs
--- a/Implab/Parallels/BlockingQueue.cs
+++ b/Implab/Parallels/BlockingQueue.cs
@@ -23,16 +23,21 @@ namespace Implab.Parallels {
 
         public T GetItem(int timeout) {
             T item;
-            var t1 = Environment.TickCount;
-            var dt = timeout;
-            while (!TryDequeue(out item)) {
-                lock (m_lock)
-                    if (!Monitor.Wait(m_lock, dt))
-                        throw new TimeoutException();
-                if (timeout >= 0) {
-                    dt = timeout - Environment.TickCount + t1;
-                    if (dt < 0)
-                        throw new TimeoutException();
+
+            if (!TryDequeue(out item)) {
+                var t1 = Environment.TickCount;
+                var dt = timeout;
+
+                lock (m_lock) {
+                    while (!TryDequeue(out item)) {
+                        if (!Monitor.Wait(m_lock, dt))
+                            throw new TimeoutException();
+                        if (timeout >= 0) {
+                            dt = timeout - Environment.TickCount + t1;
+                            if (dt < 0)
+                                throw new TimeoutException();
+                        }
+                    }
                 }
             }
             return item;
@@ -40,9 +45,11 @@ namespace Implab.Parallels {
 
         public T GetItem() {
             T item;
-            while (!TryDequeue(out item))
-                lock (m_lock)
-                    Monitor.Wait(m_lock);
+            if (!TryDequeue(out item))
+                lock (m_lock) {
+                    while (!TryDequeue(out item))
+                        Monitor.Wait(m_lock);
+                }
             return item;
         }
 
@@ -51,16 +58,22 @@ namespace Implab.Parallels {
 
             var buffer = new T[max];
             int actual;
-            var t1 = Environment.TickCount;
-            var dt = timeout;
-            while (!TryDequeueRange(buffer,0,max,out actual)) {
-                lock (m_lock)
-                    if (!Monitor.Wait(m_lock, dt))
-                        throw new TimeoutException();
-                if (timeout >= 0) {
-                    dt = timeout - Environment.TickCount + t1;
-                    if (dt < 0)
-                        throw new TimeoutException();
+            if (!TryDequeueRange(buffer, 0, max, out actual)) {
+                var t1 = Environment.TickCount;
+                var dt = timeout;
+
+                lock (m_lock) {
+                    while (!TryDequeueRange(buffer, 0, max, out actual)) {
+                
+                        if (!Monitor.Wait(m_lock, dt))
+                            throw new TimeoutException();
+
+                        if (timeout >= 0) {
+                            dt = timeout - Environment.TickCount + t1;
+                            if (dt < 0)
+                                throw new TimeoutException();
+                        }
+                    }
                 }
             }
 
@@ -74,9 +87,10 @@ namespace Implab.Parallels {
 
             var buffer = new T[max];
             int actual;
-            while (!TryDequeueRange(buffer, 0, max, out actual))
+            if (!TryDequeueRange(buffer, 0, max, out actual))
                 lock (m_lock)
-                    Monitor.Wait(m_lock);
+                    while (!TryDequeueRange(buffer, 0, max, out actual))
+                        Monitor.Wait(m_lock);
 
             var data = new T[actual];
             Array.Copy(buffer, data, actual);