Update SmartThreadPool to latest version 2.2.3 with a major and minor change.

SmartThreadPool code comes from http://www.codeproject.com/Articles/7933/Smart-Thread-Pool
This version implements thread abort (via WorkItem.Cancel(true)), threadpool naming, max thread stack, etc. so we no longer need to manually patch those.
However, two changes have been made to stock 2.2.3.
Major change: WorkItem.Cancel(bool abortExecution) in our version does not succeed if the work item was in progress and thread abort was not specified.
This is to match previous behaviour where we handle co-operative termination via another mechanism rather than checking WorkItem.IsCanceled.
Minor change: Did not add STP's StopWatch implementation as this is only used WinCE and Silverlight and causes a build clash with System.Diagnostics.StopWatch
The reason for updating is to see if this improves http://opensimulator.org/mantis/view.php?id=6557 and http://opensimulator.org/mantis/view.php?id=6586

1 files changed, 303 insertions, 346 deletions

diff --git a/ThirdParty/SmartThreadPool/WorkItem.cs b/ThirdParty/SmartThreadPool/WorkItem.cs
index d0c0524..f229d1f 100644
--- a/ThirdParty/SmartThreadPool/WorkItem.cs
+++ b/ThirdParty/SmartThreadPool/WorkItem.cs
@@ -1,58 +1,13 @@
-// Ami Bar
-// amibar@gmail.com
-
 using System;
 using System.Threading;
 using System.Diagnostics;
 
 namespace Amib.Threading.Internal
 {
-    #region WorkItem Delegate
-
-    /// <summary>
-    /// An internal delegate to call when the WorkItem starts or completes
-    /// </summary>
-    internal delegate void WorkItemStateCallback(WorkItem workItem);
-
-    #endregion
-
-    #region IInternalWorkItemResult interface 
-
-    public class CanceledWorkItemsGroup
-    {
-        public readonly static CanceledWorkItemsGroup NotCanceledWorkItemsGroup = new CanceledWorkItemsGroup();
-
-        private bool _isCanceled = false;
-        public bool IsCanceled 
-        { 
-            get { return _isCanceled; }
-            set { _isCanceled = value; }
-        }
-    }
-
-    internal interface IInternalWorkItemResult
-    {
-        event WorkItemStateCallback OnWorkItemStarted;
-        event WorkItemStateCallback OnWorkItemCompleted;
-    }
-
-    #endregion
-
-    #region IWorkItem interface
-
-    public interface IWorkItem
-    {
-
-    }
-
-    #endregion
-
-    #region WorkItem class
-
     /// <summary>
     /// Holds a callback delegate and the state for that delegate.
     /// </summary>
-    public class WorkItem : IHasWorkItemPriority, IWorkItem
+    public partial class WorkItem : IHasWorkItemPriority
     {
         #region WorkItemState enum
 
@@ -61,33 +16,57 @@ namespace Amib.Threading.Internal
         /// </summary>
         private enum WorkItemState
         {
-            InQueue,
-            InProgress,
-            Completed,
-            Canceled,
+            InQueue = 0,    // Nexts: InProgress, Canceled
+            InProgress = 1,    // Nexts: Completed, Canceled
+            Completed = 2,    // Stays Completed
+            Canceled = 3,    // Stays Canceled
         }
 
-        #endregion
+        private static bool IsValidStatesTransition(WorkItemState currentState, WorkItemState nextState)
+        {
+            bool valid = false;
+
+            switch (currentState)
+            {
+                case WorkItemState.InQueue:
+                    valid = (WorkItemState.InProgress == nextState) || (WorkItemState.Canceled == nextState);
+                    break;
+                case WorkItemState.InProgress:
+                    valid = (WorkItemState.Completed == nextState) || (WorkItemState.Canceled == nextState);
+                    break;
+                case WorkItemState.Completed:
+                case WorkItemState.Canceled:
+                    // Cannot be changed
+                    break;
+                default:
+                    // Unknown state
+                    Debug.Assert(false);
+                    break;
+            }
 
-        #region Member Variables
+            return valid;
+        }
 
-        public Thread currentThread;
+        #endregion
+
+        #region Fields
 
         /// <summary>
         /// Callback delegate for the callback.
         /// </summary>
-        private WorkItemCallback _callback;
+        private readonly WorkItemCallback _callback;
 
         /// <summary>
         /// State with which to call the callback delegate.
         /// </summary>
         private object _state;
 
+#if !(_WINDOWS_CE) && !(_SILVERLIGHT) && !(WINDOWS_PHONE)
         /// <summary>
         /// Stores the caller's context
         /// </summary>
-        private CallerThreadContext _callerContext;
-
+        private readonly CallerThreadContext _callerContext;
+#endif
         /// <summary>
         /// Holds the result of the mehtod
         /// </summary>
@@ -117,12 +96,12 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Represents the result state of the work item
         /// </summary>
-        private WorkItemResult _workItemResult;
+        private readonly WorkItemResult _workItemResult;
 
         /// <summary>
         /// Work item info
         /// </summary>
-        private WorkItemInfo _workItemInfo;
+        private readonly WorkItemInfo _workItemInfo;
 
         /// <summary>
         /// Called when the WorkItem starts
@@ -141,30 +120,41 @@ namespace Amib.Threading.Internal
         private CanceledWorkItemsGroup _canceledWorkItemsGroup = CanceledWorkItemsGroup.NotCanceledWorkItemsGroup;
 
         /// <summary>
+        /// A reference to an object that indicates whatever the 
+        /// SmartThreadPool has been canceled
+        /// </summary>
+        private CanceledWorkItemsGroup _canceledSmartThreadPool = CanceledWorkItemsGroup.NotCanceledWorkItemsGroup;
+
+        /// <summary>
         /// The work item group this work item belong to.
-        /// 
         /// </summary>
-        private IWorkItemsGroup _workItemsGroup;
+        private readonly IWorkItemsGroup _workItemsGroup;
 
-        #region Performance Counter fields
+        /// <summary>
+        /// The thread that executes this workitem.
+        /// This field is available for the period when the work item is executed, before and after it is null.
+        /// </summary>
+        private Thread _executingThread;
 
         /// <summary>
-        /// The time when the work items is queued.
-        /// Used with the performance counter.
+        /// The absulote time when the work item will be timeout
         /// </summary>
-        private DateTime _queuedTime;
+        private long _expirationTime;
+
+        #region Performance Counter fields
+
+
+
 
         /// <summary>
-        /// The time when the work items starts its execution.
-        /// Used with the performance counter.
+        /// Stores how long the work item waited on the stp queue
         /// </summary>
-        private DateTime _beginProcessTime;
+        private Stopwatch _waitingOnQueueStopwatch;
 
         /// <summary>
-        /// The time when the work items ends its execution.
-        /// Used with the performance counter.
+        /// Stores how much time it took the work item to execute after it went out of the queue
         /// </summary>
-        private DateTime _endProcessTime;
+        private Stopwatch _processingStopwatch;
 
         #endregion
 
@@ -174,17 +164,25 @@ namespace Amib.Threading.Internal
 
         public TimeSpan WaitingTime
         {
-            get 
+            get
             {
-                return (_beginProcessTime - _queuedTime);
+                return _waitingOnQueueStopwatch.Elapsed;
             }
         }
 
         public TimeSpan ProcessTime
         {
-            get 
+            get
+            {
+                return _processingStopwatch.Elapsed;
+            }
+        }
+
+        internal WorkItemInfo WorkItemInfo
+        {
+            get
             {
-                return (_endProcessTime - _beginProcessTime);
+                return _workItemInfo;
             }
         }
 
@@ -195,6 +193,8 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Initialize the callback holding object.
         /// </summary>
+        /// <param name="workItemsGroup">The workItemGroup of the workitem</param>
+        /// <param name="workItemInfo">The WorkItemInfo of te workitem</param>
         /// <param name="callback">Callback delegate for the callback.</param>
         /// <param name="state">State with which to call the callback delegate.</param>
         /// 
@@ -203,16 +203,18 @@ namespace Amib.Threading.Internal
         public WorkItem(
             IWorkItemsGroup workItemsGroup,
             WorkItemInfo workItemInfo,
-            WorkItemCallback callback, 
+            WorkItemCallback callback,
             object state)
         {
             _workItemsGroup = workItemsGroup;
             _workItemInfo = workItemInfo;
 
+#if !(_WINDOWS_CE) && !(_SILVERLIGHT) && !(WINDOWS_PHONE)
             if (_workItemInfo.UseCallerCallContext || _workItemInfo.UseCallerHttpContext)
             {
                 _callerContext = CallerThreadContext.Capture(_workItemInfo.UseCallerCallContext, _workItemInfo.UseCallerHttpContext);
             }
+#endif
 
             _callback = callback;
             _state = state;
@@ -222,9 +224,18 @@ namespace Amib.Threading.Internal
 
         internal void Initialize()
         {
+            // The _workItemState is changed directly instead of using the SetWorkItemState
+            // method since we don't want to go throught IsValidStateTransition.
             _workItemState = WorkItemState.InQueue;
+
             _workItemCompleted = null;
             _workItemCompletedRefCount = 0;
+            _waitingOnQueueStopwatch = new Stopwatch();
+            _processingStopwatch = new Stopwatch();
+            _expirationTime =
+                _workItemInfo.Timeout > 0 ?
+                DateTime.UtcNow.Ticks + _workItemInfo.Timeout * TimeSpan.TicksPerMillisecond :
+                long.MaxValue;
         }
 
         internal bool WasQueuedBy(IWorkItemsGroup workItemsGroup)
@@ -237,17 +248,16 @@ namespace Amib.Threading.Internal
 
         #region Methods
 
-        public CanceledWorkItemsGroup CanceledWorkItemsGroup
+        internal CanceledWorkItemsGroup CanceledWorkItemsGroup
         {
-            get
-            {
-                return _canceledWorkItemsGroup;
-            }
+            get { return _canceledWorkItemsGroup; }
+            set { _canceledWorkItemsGroup = value; }
+        }
 
-            set
-            {
-                _canceledWorkItemsGroup = value;
-            }
+        internal CanceledWorkItemsGroup CanceledSmartThreadPool
+        {
+            get { return _canceledSmartThreadPool; }
+            set { _canceledSmartThreadPool = value; }
         }
 
         /// <summary>
@@ -259,9 +269,10 @@ namespace Amib.Threading.Internal
         /// </returns>
         public bool StartingWorkItem()
         {
-            _beginProcessTime = DateTime.Now;
+            _waitingOnQueueStopwatch.Stop();
+            _processingStopwatch.Start();
 
-            lock(this)
+            lock (this)
             {
                 if (IsCanceled)
                 {
@@ -277,6 +288,9 @@ namespace Amib.Threading.Internal
 
                 Debug.Assert(WorkItemState.InQueue == GetWorkItemState());
 
+                // No need for a lock yet, only after the state has changed to InProgress
+                _executingThread = Thread.CurrentThread;
+
                 SetWorkItemState(WorkItemState.InProgress);
             }
 
@@ -291,7 +305,7 @@ namespace Amib.Threading.Internal
             CallToPostExecute currentCallToPostExecute = 0;
 
             // Execute the work item if we are in the correct state
-            switch(GetWorkItemState())
+            switch (GetWorkItemState())
             {
                 case WorkItemState.InProgress:
                     currentCallToPostExecute |= CallToPostExecute.WhenWorkItemNotCanceled;
@@ -311,7 +325,7 @@ namespace Amib.Threading.Internal
                 PostExecute();
             }
 
-            _endProcessTime = DateTime.Now;
+            _processingStopwatch.Stop();
         }
 
         internal void FireWorkItemCompleted()
@@ -323,8 +337,21 @@ namespace Amib.Threading.Internal
                     _workItemCompletedEvent(this);
                 }
             }
-            catch // Ignore exceptions
-            {}
+            catch // Suppress exceptions
+            { }
+        }
+
+        internal void FireWorkItemStarted()
+        {
+            try
+            {
+                if (null != _workItemStartedEvent)
+                {
+                    _workItemStartedEvent(this);
+                }
+            }
+            catch // Suppress exceptions
+            { }
         }
 
         /// <summary>
@@ -332,32 +359,70 @@ namespace Amib.Threading.Internal
         /// </summary>
         private void ExecuteWorkItem()
         {
+
+#if !(_WINDOWS_CE) && !(_SILVERLIGHT) && !(WINDOWS_PHONE)
             CallerThreadContext ctc = null;
             if (null != _callerContext)
             {
                 ctc = CallerThreadContext.Capture(_callerContext.CapturedCallContext, _callerContext.CapturedHttpContext);
                 CallerThreadContext.Apply(_callerContext);
             }
+#endif
 
             Exception exception = null;
             object result = null;
 
             try
             {
-                result = _callback(_state);
+                try
+                {
+                    result = _callback(_state);
+                }
+                catch (Exception e)
+                {
+                    // Save the exception so we can rethrow it later
+                    exception = e;
+                }
+
+                // Remove the value of the execution thread, so it will be impossible to cancel the work item,
+                // since it is already completed.
+                // Cancelling a work item that already completed may cause the abortion of the next work item!!!
+                Thread executionThread = Interlocked.CompareExchange(ref _executingThread, null, _executingThread);
+
+                if (null == executionThread)
+                {
+                    // Oops! we are going to be aborted..., Wait here so we can catch the ThreadAbortException
+                    Thread.Sleep(60 * 1000);
+
+                    // If after 1 minute this thread was not aborted then let it continue working.
+                }
             }
-            catch (Exception e) 
+            // We must treat the ThreadAbortException or else it will be stored in the exception variable
+            catch (ThreadAbortException tae)
             {
-                // Save the exception so we can rethrow it later
-                exception = e;
+                tae.GetHashCode();
+                // Check if the work item was cancelled
+                // If we got a ThreadAbortException and the STP is not shutting down, it means the 
+                // work items was cancelled.
+                if (!SmartThreadPool.CurrentThreadEntry.AssociatedSmartThreadPool.IsShuttingdown)
+                {
+#if !(_WINDOWS_CE) && !(_SILVERLIGHT) && !(WINDOWS_PHONE)
+                    Thread.ResetAbort();
+#endif
+                }
             }
-        
+
+#if !(_WINDOWS_CE) && !(_SILVERLIGHT) && !(WINDOWS_PHONE)
             if (null != _callerContext)
             {
                 CallerThreadContext.Apply(ctc);
             }
+#endif
 
-            SetResult(result, exception);
+            if (!SmartThreadPool.IsWorkItemCanceled)
+            {
+                SetResult(result, exception);
+            }
         }
 
         /// <summary>
@@ -369,9 +434,9 @@ namespace Amib.Threading.Internal
             {
                 try
                 {
-                    _workItemInfo.PostExecuteWorkItemCallback(this._workItemResult);
+                    _workItemInfo.PostExecuteWorkItemCallback(_workItemResult);
                 }
-                catch (Exception e) 
+                catch (Exception e)
                 {
                     Debug.Assert(null != e);
                 }
@@ -382,6 +447,8 @@ namespace Amib.Threading.Internal
         /// Set the result of the work item to return
         /// </summary>
         /// <param name="result">The result of the work item</param>
+        /// <param name="exception">The exception that was throw while the workitem executed, null
+        /// if there was no exception.</param>
         internal void SetResult(object result, Exception exception)
         {
             _result = result;
@@ -401,48 +468,48 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Wait for all work items to complete
         /// </summary>
-        /// <param name="workItemResults">Array of work item result objects</param>
+        /// <param name="waitableResults">Array of work item result objects</param>
         /// <param name="millisecondsTimeout">The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.</param>
         /// <param name="exitContext">
         /// true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it; otherwise, false. 
         /// </param>
         /// <param name="cancelWaitHandle">A cancel wait handle to interrupt the wait if needed</param>
         /// <returns>
-        /// true when every work item in workItemResults has completed; otherwise false.
+        /// true when every work item in waitableResults has completed; otherwise false.
         /// </returns>
         internal static bool WaitAll(
-            IWorkItemResult [] workItemResults,
+            IWaitableResult[] waitableResults,
             int millisecondsTimeout,
             bool exitContext,
             WaitHandle cancelWaitHandle)
         {
-            if (0 == workItemResults.Length)
+            if (0 == waitableResults.Length)
             {
                 return true;
             }
 
             bool success;
-            WaitHandle [] waitHandles = new WaitHandle[workItemResults.Length];;
-            GetWaitHandles(workItemResults, waitHandles);
+            WaitHandle[] waitHandles = new WaitHandle[waitableResults.Length];
+            GetWaitHandles(waitableResults, waitHandles);
 
             if ((null == cancelWaitHandle) && (waitHandles.Length <= 64))
             {
-                success = WaitHandle.WaitAll(waitHandles, millisecondsTimeout, exitContext);
+                success = STPEventWaitHandle.WaitAll(waitHandles, millisecondsTimeout, exitContext);
             }
             else
             {
                 success = true;
                 int millisecondsLeft = millisecondsTimeout;
-                DateTime start = DateTime.Now;
+                Stopwatch stopwatch = Stopwatch.StartNew();
 
-                WaitHandle [] whs;
+                WaitHandle[] whs;
                 if (null != cancelWaitHandle)
                 {
-                    whs = new WaitHandle [] { null, cancelWaitHandle };
+                    whs = new WaitHandle[] { null, cancelWaitHandle };
                 }
                 else
                 {
-                    whs = new WaitHandle [] { null };
+                    whs = new WaitHandle[] { null };
                 }
 
                 bool waitInfinitely = (Timeout.Infinite == millisecondsTimeout);
@@ -450,7 +517,7 @@ namespace Amib.Threading.Internal
                 // We cannot use WaitHandle.WaitAll directly, because the cancelWaitHandle
                 // won't affect it.
                 // Each iteration we update the time left for the timeout.
-                for(int i = 0; i < workItemResults.Length; ++i)
+                for (int i = 0; i < waitableResults.Length; ++i)
                 {
                     // WaitAny don't work with negative numbers
                     if (!waitInfinitely && (millisecondsLeft < 0))
@@ -460,23 +527,22 @@ namespace Amib.Threading.Internal
                     }
 
                     whs[0] = waitHandles[i];
-                    int result = WaitHandle.WaitAny(whs, millisecondsLeft, exitContext);
-                    if((result > 0) || (WaitHandle.WaitTimeout == result))
+                    int result = STPEventWaitHandle.WaitAny(whs, millisecondsLeft, exitContext);
+                    if ((result > 0) || (STPEventWaitHandle.WaitTimeout == result))
                     {
                         success = false;
                         break;
                     }
 
-                    if(!waitInfinitely)
+                    if (!waitInfinitely)
                     {
                         // Update the time left to wait
-                        TimeSpan ts = DateTime.Now - start;
-                        millisecondsLeft = millisecondsTimeout - (int)ts.TotalMilliseconds;
+                        millisecondsLeft = millisecondsTimeout - (int)stopwatch.ElapsedMilliseconds;
                     }
                 }
             }
             // Release the wait handles
-            ReleaseWaitHandles(workItemResults);
+            ReleaseWaitHandles(waitableResults);
 
             return success;
         }
@@ -484,7 +550,7 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Waits for any of the work items in the specified array to complete, cancel, or timeout
         /// </summary>
-        /// <param name="workItemResults">Array of work item result objects</param>
+        /// <param name="waitableResults">Array of work item result objects</param>
         /// <param name="millisecondsTimeout">The number of milliseconds to wait, or Timeout.Infinite (-1) to wait indefinitely.</param>
         /// <param name="exitContext">
         /// true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it; otherwise, false. 
@@ -493,38 +559,38 @@ namespace Amib.Threading.Internal
         /// <returns>
         /// The array index of the work item result that satisfied the wait, or WaitTimeout if no work item result satisfied the wait and a time interval equivalent to millisecondsTimeout has passed or the work item has been canceled.
         /// </returns>
-        internal static int WaitAny(            
-            IWorkItemResult [] workItemResults,
+        internal static int WaitAny(
+            IWaitableResult[] waitableResults,
             int millisecondsTimeout,
             bool exitContext,
             WaitHandle cancelWaitHandle)
         {
-            WaitHandle [] waitHandles = null;
+            WaitHandle[] waitHandles;
 
             if (null != cancelWaitHandle)
             {
-                waitHandles = new WaitHandle[workItemResults.Length+1];
-                GetWaitHandles(workItemResults, waitHandles);
-                waitHandles[workItemResults.Length] = cancelWaitHandle;
+                waitHandles = new WaitHandle[waitableResults.Length + 1];
+                GetWaitHandles(waitableResults, waitHandles);
+                waitHandles[waitableResults.Length] = cancelWaitHandle;
             }
             else
             {
-                waitHandles = new WaitHandle[workItemResults.Length];
-                GetWaitHandles(workItemResults, waitHandles);
+                waitHandles = new WaitHandle[waitableResults.Length];
+                GetWaitHandles(waitableResults, waitHandles);
             }
 
-            int result = WaitHandle.WaitAny(waitHandles, millisecondsTimeout, exitContext);
+            int result = STPEventWaitHandle.WaitAny(waitHandles, millisecondsTimeout, exitContext);
 
             // Treat cancel as timeout
             if (null != cancelWaitHandle)
             {
-                if (result == workItemResults.Length)
+                if (result == waitableResults.Length)
                 {
-                    result = WaitHandle.WaitTimeout;
+                    result = STPEventWaitHandle.WaitTimeout;
                 }
             }
 
-            ReleaseWaitHandles(workItemResults);
+            ReleaseWaitHandles(waitableResults);
 
             return result;
         }
@@ -532,16 +598,16 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Fill an array of wait handles with the work items wait handles.
         /// </summary>
-        /// <param name="workItemResults">An array of work item results</param>
+        /// <param name="waitableResults">An array of work item results</param>
         /// <param name="waitHandles">An array of wait handles to fill</param>
         private static void GetWaitHandles(
-            IWorkItemResult [] workItemResults,
-            WaitHandle [] waitHandles)
+            IWaitableResult[] waitableResults,
+            WaitHandle[] waitHandles)
         {
-            for(int i = 0; i < workItemResults.Length; ++i)
+            for (int i = 0; i < waitableResults.Length; ++i)
             {
-                WorkItemResult wir = workItemResults[i] as WorkItemResult;
-                Debug.Assert(null != wir, "All workItemResults must be WorkItemResult objects");
+                WorkItemResult wir = waitableResults[i].GetWorkItemResult() as WorkItemResult;
+                Debug.Assert(null != wir, "All waitableResults must be WorkItemResult objects");
 
                 waitHandles[i] = wir.GetWorkItem().GetWaitHandle();
             }
@@ -550,40 +616,64 @@ namespace Amib.Threading.Internal
         /// <summary>
         /// Release the work items' wait handles
         /// </summary>
-        /// <param name="workItemResults">An array of work item results</param>
-        private static void ReleaseWaitHandles(IWorkItemResult [] workItemResults)
+        /// <param name="waitableResults">An array of work item results</param>
+        private static void ReleaseWaitHandles(IWaitableResult[] waitableResults)
         {
-            for(int i = 0; i < workItemResults.Length; ++i)
+            for (int i = 0; i < waitableResults.Length; ++i)
             {
-                WorkItemResult wir = workItemResults[i] as WorkItemResult;
+                WorkItemResult wir = (WorkItemResult)waitableResults[i].GetWorkItemResult();
 
                 wir.GetWorkItem().ReleaseWaitHandle();
             }
         }
 
-
         #endregion
-        
+
         #region Private Members
 
         private WorkItemState GetWorkItemState()
         {
-            if (_canceledWorkItemsGroup.IsCanceled)
+            lock (this)
             {
-                return WorkItemState.Canceled;
-            }
-            return _workItemState;
+                if (WorkItemState.Completed == _workItemState)
+                {
+                    return _workItemState;
+                }
+
+                long nowTicks = DateTime.UtcNow.Ticks;
 
+                if (WorkItemState.Canceled != _workItemState && nowTicks > _expirationTime)
+                {
+                    _workItemState = WorkItemState.Canceled;
+                }
+
+                if (WorkItemState.InProgress == _workItemState)
+                {
+                    return _workItemState;
+                }
+
+                if (CanceledSmartThreadPool.IsCanceled || CanceledWorkItemsGroup.IsCanceled)
+                {
+                    return WorkItemState.Canceled;
+                }
+
+                return _workItemState;
+            }
         }
+
+
         /// <summary>
         /// Sets the work item's state
         /// </summary>
         /// <param name="workItemState">The state to set the work item to</param>
         private void SetWorkItemState(WorkItemState workItemState)
         {
-            lock(this)
+            lock (this)
             {
-                _workItemState = workItemState;
+                if (IsValidStatesTransition(_workItemState, workItemState))
+                {
+                    _workItemState = workItemState;
+                }
             }
         }
 
@@ -594,7 +684,7 @@ namespace Amib.Threading.Internal
         private void SignalComplete(bool canceled)
         {
             SetWorkItemState(canceled ? WorkItemState.Canceled : WorkItemState.Completed);
-            lock(this)
+            lock (this)
             {
                 // If someone is waiting then signal.
                 if (null != _workItemCompleted)
@@ -606,40 +696,83 @@ namespace Amib.Threading.Internal
 
         internal void WorkItemIsQueued()
         {
-            _queuedTime = DateTime.Now;
+            _waitingOnQueueStopwatch.Start();
         }
 
         #endregion
-        
+
         #region Members exposed by WorkItemResult
 
         /// <summary>
         /// Cancel the work item if it didn't start running yet.
         /// </summary>
         /// <returns>Returns true on success or false if the work item is in progress or already completed</returns>
-        private bool Cancel()
+        private bool Cancel(bool abortExecution)
         {
-            lock(this)
+#if (_WINDOWS_CE)
+            if(abortExecution)
+            {
+                throw new ArgumentOutOfRangeException("abortExecution", "WindowsCE doesn't support this feature");
+            }
+#endif
+            bool success = false;
+            bool signalComplete = false;
+
+            lock (this)
             {
-                switch(GetWorkItemState())
+                switch (GetWorkItemState())
                 {
                     case WorkItemState.Canceled:
                         //Debug.WriteLine("Work item already canceled");
-                        return true;
+                        if (abortExecution)
+                        {
+                            Thread executionThread = Interlocked.CompareExchange(ref _executingThread, null, _executingThread);
+                            if (null != executionThread)
+                            {
+                                executionThread.Abort(); // "Cancel"
+                                // No need to signalComplete, because we already cancelled this work item
+                                // so it already signaled its completion.
+                                //signalComplete = true;
+                            }
+                        } 
+                        success = true;
+                        break;
                     case WorkItemState.Completed:
-                    case WorkItemState.InProgress:
                         //Debug.WriteLine("Work item cannot be canceled");
-                        return false;
+                        break;
+                    case WorkItemState.InProgress:
+                        if (abortExecution)
+                        {
+                            Thread executionThread = Interlocked.CompareExchange(ref _executingThread, null, _executingThread);
+                            if (null != executionThread)
+                            {
+                                executionThread.Abort(); // "Cancel"
+                                success = true;
+                                signalComplete = true;
+                            }
+                        }
+                        else
+                        {
+                            success = false;
+                            signalComplete = false;
+                        }
+                        break;
                     case WorkItemState.InQueue:
                         // Signal to the wait for completion that the work
                         // item has been completed (canceled). There is no
                         // reason to wait for it to get out of the queue
-                        SignalComplete(true);
+                        signalComplete = true;
                         //Debug.WriteLine("Work item canceled");
-                        return true;
+                        success = true;
+                        break;
+                }
+
+                if (signalComplete)
+                {
+                    SignalComplete(true);
                 }
             }
-            return false;
+            return success;
         }
 
         /// <summary>
@@ -653,7 +786,7 @@ namespace Amib.Threading.Internal
             bool exitContext,
             WaitHandle cancelWaitHandle)
         {
-            Exception e = null;
+            Exception e;
             object result = GetResult(millisecondsTimeout, exitContext, cancelWaitHandle, out e);
             if (null != e)
             {
@@ -694,7 +827,7 @@ namespace Amib.Threading.Internal
             {
                 WaitHandle wh = GetWaitHandle();
 
-                bool timeout = !wh.WaitOne(millisecondsTimeout, exitContext);
+                bool timeout = !STPEventWaitHandle.WaitOne(wh, millisecondsTimeout, exitContext);
 
                 ReleaseWaitHandle();
 
@@ -706,10 +839,10 @@ namespace Amib.Threading.Internal
             else
             {
                 WaitHandle wh = GetWaitHandle();
-                int result = WaitHandle.WaitAny(new WaitHandle[] { wh, cancelWaitHandle });
+                int result = STPEventWaitHandle.WaitAny(new WaitHandle[] { wh, cancelWaitHandle });
                 ReleaseWaitHandle();
 
-                switch(result)
+                switch (result)
                 {
                     case 0:
                         // The work item signaled
@@ -717,7 +850,7 @@ namespace Amib.Threading.Internal
                         // work item (not the get result)
                         break;
                     case 1:
-                    case WaitHandle.WaitTimeout:
+                    case STPEventWaitHandle.WaitTimeout:
                         throw new WorkItemTimeoutException("Work item timeout");
                     default:
                         Debug.Assert(false);
@@ -745,11 +878,11 @@ namespace Amib.Threading.Internal
         /// </summary>
         private WaitHandle GetWaitHandle()
         {
-            lock(this)
+            lock (this)
             {
                 if (null == _workItemCompleted)
                 {
-                    _workItemCompleted = new ManualResetEvent(IsCompleted);
+                    _workItemCompleted = EventWaitHandleFactory.CreateManualResetEvent(IsCompleted);
                 }
                 ++_workItemCompletedRefCount;
             }
@@ -758,7 +891,7 @@ namespace Amib.Threading.Internal
 
         private void ReleaseWaitHandle()
         {
-            lock(this)
+            lock (this)
             {
                 if (null != _workItemCompleted)
                 {
@@ -779,10 +912,10 @@ namespace Amib.Threading.Internal
         {
             get
             {
-                lock(this)
+                lock (this)
                 {
                     WorkItemState workItemState = GetWorkItemState();
-                    return ((workItemState == WorkItemState.Completed) || 
+                    return ((workItemState == WorkItemState.Completed) ||
                             (workItemState == WorkItemState.Canceled));
                 }
             }
@@ -795,7 +928,7 @@ namespace Amib.Threading.Internal
         {
             get
             {
-                lock(this)
+                lock (this)
                 {
                     return (GetWorkItemState() == WorkItemState.Canceled);
                 }
@@ -843,172 +976,6 @@ namespace Amib.Threading.Internal
             }
         }
 
-
-        #region WorkItemResult class
-
-        private class WorkItemResult : IWorkItemResult, IInternalWorkItemResult
-        {
-            /// <summary>
-            /// A back reference to the work item
-            /// </summary>
-            private WorkItem _workItem;
-
-            public WorkItemResult(WorkItem workItem)
-            {
-                _workItem = workItem;
-            }
-
-            internal WorkItem GetWorkItem()
-            {
-                return _workItem;
-            }
-
-            #region IWorkItemResult Members
-
-            public bool IsCompleted
-            {
-                get
-                {
-                    return _workItem.IsCompleted;
-                }
-            }
-
-            public void Abort()
-            {
-                _workItem.Abort();
-            }
-
-            public bool IsCanceled
-            {
-                get
-                {
-                    return _workItem.IsCanceled;
-                }
-            }
-
-            public object GetResult()
-            {
-                return _workItem.GetResult(Timeout.Infinite, true, null);
-            }
-    
-            public object GetResult(int millisecondsTimeout, bool exitContext)
-            {
-                return _workItem.GetResult(millisecondsTimeout, exitContext, null);
-            }
-
-            public object GetResult(TimeSpan timeout, bool exitContext)
-            {
-                return _workItem.GetResult((int)timeout.TotalMilliseconds, exitContext, null);
-            }
-
-            public object GetResult(int millisecondsTimeout, bool exitContext, WaitHandle cancelWaitHandle)
-            {
-                return _workItem.GetResult(millisecondsTimeout, exitContext, cancelWaitHandle);
-            }
-
-            public object GetResult(TimeSpan timeout, bool exitContext, WaitHandle cancelWaitHandle)
-            {
-                return _workItem.GetResult((int)timeout.TotalMilliseconds, exitContext, cancelWaitHandle);
-            }
-
-            public object GetResult(out Exception e)
-            {
-                return _workItem.GetResult(Timeout.Infinite, true, null, out e);
-            }
-    
-            public object GetResult(int millisecondsTimeout, bool exitContext, out Exception e)
-            {
-                return _workItem.GetResult(millisecondsTimeout, exitContext, null, out e);
-            }
-
-            public object GetResult(TimeSpan timeout, bool exitContext, out Exception e)
-            {
-                return _workItem.GetResult((int)timeout.TotalMilliseconds, exitContext, null, out e);
-            }
-
-            public object GetResult(int millisecondsTimeout, bool exitContext, WaitHandle cancelWaitHandle, out Exception e)
-            {
-                return _workItem.GetResult(millisecondsTimeout, exitContext, cancelWaitHandle, out e);
-            }
-
-            public object GetResult(TimeSpan timeout, bool exitContext, WaitHandle cancelWaitHandle, out Exception e)
-            {
-                return _workItem.GetResult((int)timeout.TotalMilliseconds, exitContext, cancelWaitHandle, out e);
-            }
-
-            public bool Cancel()
-            {
-                return _workItem.Cancel();
-            }
-
-            public object State
-            {
-                get
-                {
-                    return _workItem._state;
-                }
-            }
-
-            public WorkItemPriority WorkItemPriority 
-            { 
-                get
-                {
-                    return _workItem._workItemInfo.WorkItemPriority;
-                }
-            }
-
-            /// <summary>
-            /// Return the result, same as GetResult()
-            /// </summary>
-            public object Result
-            {
-                get { return GetResult(); }
-            }
-
-            /// <summary>
-            /// Returns the exception if occured otherwise returns null.
-            /// This value is valid only after the work item completed,
-            /// before that it is always null.
-            /// </summary>
-            public object Exception
-            {
-                get { return _workItem._exception; }
-            }
-
-            #endregion
-
-            #region IInternalWorkItemResult Members
-
-            public event WorkItemStateCallback OnWorkItemStarted
-            {
-                add
-                {
-                    _workItem.OnWorkItemStarted += value;
-                }
-                remove
-                {
-                    _workItem.OnWorkItemStarted -= value;
-                }
-            }
-
-
-            public event WorkItemStateCallback OnWorkItemCompleted
-            {
-                add
-                {
-                    _workItem.OnWorkItemCompleted += value;
-                }
-                remove
-                {
-                    _workItem.OnWorkItemCompleted -= value;
-                }
-            }
-
-            #endregion
-        }
-
-        #endregion
-
         public void DisposeOfState()
         {
             if (_workItemInfo.DisposeOfStateObjects)
@@ -1021,15 +988,5 @@ namespace Amib.Threading.Internal
                 }
             }
         }
-
-        public void Abort()
-        {
-            lock (this)
-            {
-                if(currentThread != null)
-                    currentThread.Abort();
-            }
-        }
     }
-    #endregion
 }