aboutsummaryrefslogtreecommitdiffstatshomepage
path: root/ThirdParty/SmartThreadPool/SmartThreadPool.cs
blob: 2c061d70b45ff905c395e311cb2e9bb523ec84a3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
// Ami Bar
// amibar@gmail.com
//
// Smart thread pool in C#.
// 7 Aug 2004 - Initial release
// 14 Sep 2004 - Bug fixes 
// 15 Oct 2004 - Added new features
//        - Work items return result.
//        - Support waiting synchronization for multiple work items.
//        - Work items can be cancelled.
//        - Passage of the caller thread’s context to the thread in the pool.
//        - Minimal usage of WIN32 handles.
//        - Minor bug fixes.
// 26 Dec 2004 - Changes:
//        - Removed static constructors.
//      - Added finalizers.
//        - Changed Exceptions so they are serializable.
//        - Fixed the bug in one of the SmartThreadPool constructors.
//        - Changed the SmartThreadPool.WaitAll() so it will support any number of waiters. 
//        The SmartThreadPool.WaitAny() is still limited by the .NET Framework.
//        - Added PostExecute with options on which cases to call it.
//      - Added option to dispose of the state objects.
//      - Added a WaitForIdle() method that waits until the work items queue is empty.
//      - Added an STPStartInfo class for the initialization of the thread pool.
//      - Changed exception handling so if a work item throws an exception it 
//        is rethrown at GetResult(), rather then firing an UnhandledException event.
//        Note that PostExecute exception are always ignored.
// 25 Mar 2005 - Changes:
//        - Fixed lost of work items bug
// 3 Jul 2005: Changes.
//      - Fixed bug where Enqueue() throws an exception because PopWaiter() returned null, hardly reconstructed. 
// 16 Aug 2005: Changes.
//        - Fixed bug where the InUseThreads becomes negative when canceling work items. 
//
// 31 Jan 2006 - Changes:
//        - Added work items priority
//        - Removed support of chained delegates in callbacks and post executes (nobody really use this)
//        - Added work items groups
//        - Added work items groups idle event
//        - Changed SmartThreadPool.WaitAll() behavior so when it gets empty array
//          it returns true rather then throwing an exception.
//        - Added option to start the STP and the WIG as suspended
//        - Exception behavior changed, the real exception is returned by an 
//          inner exception
//        - Added option to keep the Http context of the caller thread. (Thanks to Steven T.)
//        - Added performance counters
//        - Added priority to the threads in the pool
//
// 13 Feb 2006 - Changes:
//        - Added a call to the dispose of the Performance Counter so
//          their won't be a Performance Counter leak.
//        - Added exception catch in case the Performance Counters cannot 
//          be created.

using System;
using System.Security;
using System.Threading;
using System.Collections;
using System.Diagnostics;
using System.Runtime.CompilerServices;

using Amib.Threading.Internal;

namespace Amib.Threading
{
    #region SmartThreadPool class
    /// <summary>
    /// Smart thread pool class.
    /// </summary>
    public class SmartThreadPool : IWorkItemsGroup, IDisposable
    {
        #region Default Constants

        /// <summary>
        /// Default minimum number of threads the thread pool contains. (0)
        /// </summary>
        public const int DefaultMinWorkerThreads = 0;

        /// <summary>
        /// Default maximum number of threads the thread pool contains. (25)
        /// </summary>
        public const int DefaultMaxWorkerThreads = 25;

        /// <summary>
        /// Default idle timeout in milliseconds. (One minute)
        /// </summary>
        public const int DefaultIdleTimeout = 60*1000; // One minute

        /// <summary>
        /// Indicate to copy the security context of the caller and then use it in the call. (false)
        /// </summary>
        public const bool DefaultUseCallerCallContext = false; 

        /// <summary>
        /// Indicate to copy the HTTP context of the caller and then use it in the call. (false)
        /// </summary>
        public const bool DefaultUseCallerHttpContext = false;

        /// <summary>
        /// Indicate to dispose of the state objects if they support the IDispose interface. (false)
        /// </summary>
        public const bool DefaultDisposeOfStateObjects = false; 

        /// <summary>
        /// The default option to run the post execute
        /// </summary>
        public const CallToPostExecute DefaultCallToPostExecute = CallToPostExecute.Always;

        /// <summary>
        /// The default post execute method to run. 
        /// When null it means not to call it.
        /// </summary>
        public static readonly PostExecuteWorkItemCallback DefaultPostExecuteWorkItemCallback = null;

        /// <summary>
        /// The default work item priority
        /// </summary>
        public const WorkItemPriority DefaultWorkItemPriority = WorkItemPriority.Normal;

        /// <summary>
        /// The default is to work on work items as soon as they arrive
        /// and not to wait for the start.
        /// </summary>
        public const bool DefaultStartSuspended = false;

        /// <summary>
        /// The default is not to use the performance counters
        /// </summary>
        public static readonly string DefaultPerformanceCounterInstanceName = null;

        public static readonly int DefaultStackSize = 0;

        /// <summary>
        /// The default thread priority
        /// </summary>
        public const ThreadPriority DefaultThreadPriority = ThreadPriority.Normal;

        /// <summary>
        /// The default thread pool name
        /// </summary>
        public const string DefaultThreadPoolName = "SmartThreadPool";

        #endregion

        #region Member Variables

        /// <summary>
        /// Contains the name of this instance of SmartThreadPool.
        /// Can be changed by the user.
        /// </summary>
        private string _name = DefaultThreadPoolName;

        /// <summary>
        /// Hashtable of all the threads in the thread pool.
        /// </summary>
        private Hashtable _workerThreads = Hashtable.Synchronized(new Hashtable());

        /// <summary>
        /// Queue of work items.
        /// </summary>
        private WorkItemsQueue _workItemsQueue = new WorkItemsQueue();

        /// <summary>
        /// Count the work items handled.
        /// Used by the performance counter.
        /// </summary>
        private long _workItemsProcessed = 0;

        /// <summary>
        /// Number of threads that currently work (not idle).
        /// </summary>
        private int _inUseWorkerThreads = 0;

        /// <summary>
        /// Start information to use. 
        /// It is simpler than providing many constructors.
        /// </summary>
        private STPStartInfo _stpStartInfo = new STPStartInfo();

        /// <summary>
        /// Total number of work items that are stored in the work items queue 
        /// plus the work items that the threads in the pool are working on.
        /// </summary>
        private int _currentWorkItemsCount = 0;

        /// <summary>
        /// Signaled when the thread pool is idle, i.e. no thread is busy
        /// and the work items queue is empty
        /// </summary>
        private ManualResetEvent _isIdleWaitHandle = new ManualResetEvent(true);

        /// <summary>
        /// An event to signal all the threads to quit immediately.
        /// </summary>
        private ManualResetEvent _shuttingDownEvent = new ManualResetEvent(false);

        /// <summary>
        /// A flag to indicate the threads to quit.
        /// </summary>
        private bool _shutdown = false;

        /// <summary>
        /// Counts the threads created in the pool.
        /// It is used to name the threads.
        /// </summary>
        private int _threadCounter = 0;

        /// <summary>
        /// Indicate that the SmartThreadPool has been disposed
        /// </summary>
        private bool _isDisposed = false;

        /// <summary>
        /// Event to send that the thread pool is idle
        /// </summary>
        private event EventHandler _stpIdle;

        /// <summary>
        /// On idle event
        /// </summary>
        //private event WorkItemsGroupIdleHandler _onIdle;

        /// <summary>
        /// Holds all the WorkItemsGroup instaces that have at least one 
        /// work item int the SmartThreadPool
        /// This variable is used in case of Shutdown
        /// </summary>
        private Hashtable _workItemsGroups = Hashtable.Synchronized(new Hashtable());

        /// <summary>
        /// A reference from each thread in the thread pool to its SmartThreadPool
        /// object container.
        /// With this variable a thread can know whatever it belongs to a 
        /// SmartThreadPool.
        /// </summary>
        [ThreadStatic]
        private static SmartThreadPool _smartThreadPool;

        /// <summary>
        /// A reference to the current work item a thread from the thread pool 
        /// is executing.
        /// </summary>
        [ThreadStatic]
        private static WorkItem _currentWorkItem;

        /// <summary>
        /// STP performance counters
        /// </summary>
        private ISTPInstancePerformanceCounters _pcs = NullSTPInstancePerformanceCounters.Instance;

        #endregion

        #region Construction and Finalization

        /// <summary>
        /// Constructor
        /// </summary>
        public SmartThreadPool()
        {
            Initialize();
        }

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="idleTimeout">Idle timeout in milliseconds</param>
        public SmartThreadPool(int idleTimeout)
        {
            _stpStartInfo.IdleTimeout = idleTimeout;
            Initialize();
        }

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="idleTimeout">Idle timeout in milliseconds</param>
        /// <param name="maxWorkerThreads">Upper limit of threads in the pool</param>
        public SmartThreadPool(
            int idleTimeout,
            int maxWorkerThreads)
        {
            _stpStartInfo.IdleTimeout = idleTimeout;
            _stpStartInfo.MaxWorkerThreads = maxWorkerThreads;
            Initialize();
        }

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="idleTimeout">Idle timeout in milliseconds</param>
        /// <param name="maxWorkerThreads">Upper limit of threads in the pool</param>
        /// <param name="minWorkerThreads">Lower limit of threads in the pool</param>
        public SmartThreadPool(
            int idleTimeout,
            int maxWorkerThreads,
            int minWorkerThreads)
        {
            _stpStartInfo.IdleTimeout = idleTimeout;
            _stpStartInfo.MaxWorkerThreads = maxWorkerThreads;
            _stpStartInfo.MinWorkerThreads = minWorkerThreads;
            Initialize();
        }

        /// <summary>
        /// Constructor
        /// </summary>
        public SmartThreadPool(STPStartInfo stpStartInfo)
        {
            _stpStartInfo = new STPStartInfo(stpStartInfo);
            Initialize();
        }

        private void Initialize()
        {
            Name = _stpStartInfo.ThreadPoolName;
            ValidateSTPStartInfo();

            if (null != _stpStartInfo.PerformanceCounterInstanceName)
            {
                try
                {
                    _pcs = new STPInstancePerformanceCounters(_stpStartInfo.PerformanceCounterInstanceName);
                }
                catch(Exception e)
                {
                    Debug.WriteLine("Unable to create Performance Counters: " + e.ToString());
                    _pcs = NullSTPInstancePerformanceCounters.Instance;
                }
            }

            StartOptimalNumberOfThreads();
        }

        private void StartOptimalNumberOfThreads()
        {
            int threadsCount = Math.Max(_workItemsQueue.Count, _stpStartInfo.MinWorkerThreads);
            threadsCount = Math.Min(threadsCount, _stpStartInfo.MaxWorkerThreads);
            StartThreads(threadsCount);
        }

        private void ValidateSTPStartInfo()
        {
            if (_stpStartInfo.MinWorkerThreads < 0)
            {
                throw new ArgumentOutOfRangeException(
                    "MinWorkerThreads", "MinWorkerThreads cannot be negative");
            }

            if (_stpStartInfo.MaxWorkerThreads <= 0)
            {
                throw new ArgumentOutOfRangeException(
                    "MaxWorkerThreads", "MaxWorkerThreads must be greater than zero");
            }

            if (_stpStartInfo.MinWorkerThreads > _stpStartInfo.MaxWorkerThreads)
            {
                throw new ArgumentOutOfRangeException(
                    "MinWorkerThreads, maxWorkerThreads", 
                    "MaxWorkerThreads must be greater or equal to MinWorkerThreads");
            }
        }

        private void ValidateCallback(Delegate callback)
        {
            if(callback.GetInvocationList().Length > 1)
            {
                throw new NotSupportedException("SmartThreadPool doesn't support delegates chains");
            }
        }

        #endregion

        #region Thread Processing

        /// <summary>
        /// Waits on the queue for a work item, shutdown, or timeout.
        /// </summary>
        /// <returns>
        /// Returns the WaitingCallback or null in case of timeout or shutdown.
        /// </returns>
        private WorkItem Dequeue()
        {
            WorkItem workItem = 
                _workItemsQueue.DequeueWorkItem(_stpStartInfo.IdleTimeout, _shuttingDownEvent);

            return workItem;
        }

        /// <summary>
        /// Put a new work item in the queue
        /// </summary>
        /// <param name="workItem">A work item to queue</param>
        private void Enqueue(WorkItem workItem)
        {
            Enqueue(workItem, true);
        }

        /// <summary>
        /// Put a new work item in the queue
        /// </summary>
        /// <param name="workItem">A work item to queue</param>
        internal void Enqueue(WorkItem workItem, bool incrementWorkItems)
        {
            // Make sure the workItem is not null
            Debug.Assert(null != workItem);

            if (incrementWorkItems)
            {
                IncrementWorkItemsCount();
            }

            _workItemsQueue.EnqueueWorkItem(workItem);
            workItem.WorkItemIsQueued();

            // If all the threads are busy then try to create a new one
            if ((InUseThreads + WaitingCallbacks) > _workerThreads.Count) 
            {
                StartThreads(1);
            }
        }

        private void IncrementWorkItemsCount()
        {
            _pcs.SampleWorkItems(_workItemsQueue.Count, _workItemsProcessed);

            int count = Interlocked.Increment(ref _currentWorkItemsCount);
            //Trace.WriteLine("WorkItemsCount = " + _currentWorkItemsCount.ToString());
            if (count == 1) 
            {
                //Trace.WriteLine("STP is NOT idle");
                _isIdleWaitHandle.Reset();
            }
        }

        private void DecrementWorkItemsCount()
        {
            ++_workItemsProcessed;

            // The counter counts even if the work item was cancelled
            _pcs.SampleWorkItems(_workItemsQueue.Count, _workItemsProcessed);

            int count = Interlocked.Decrement(ref _currentWorkItemsCount);
            //Trace.WriteLine("WorkItemsCount = " + _currentWorkItemsCount.ToString());
            if (count == 0) 
            {
                //Trace.WriteLine("STP is idle");
                _isIdleWaitHandle.Set();
            }
        }

        internal void RegisterWorkItemsGroup(IWorkItemsGroup workItemsGroup)
        {
            _workItemsGroups[workItemsGroup] = workItemsGroup;
        }

        internal void UnregisterWorkItemsGroup(IWorkItemsGroup workItemsGroup)
        {
            if (_workItemsGroups.Contains(workItemsGroup))
            {
                _workItemsGroups.Remove(workItemsGroup);
            }
        }

        /// <summary>
        /// Inform that the current thread is about to quit or quiting.
        /// The same thread may call this method more than once.
        /// </summary>
        private void InformCompleted()
        {
            // There is no need to lock the two methods together 
            // since only the current thread removes itself
            // and the _workerThreads is a synchronized hashtable
            if (_workerThreads.Contains(Thread.CurrentThread))
            {
                _workerThreads.Remove(Thread.CurrentThread);
                _pcs.SampleThreads(_workerThreads.Count, _inUseWorkerThreads);
            }
        }

        /// <summary>
        /// Starts new threads
        /// </summary>
        /// <param name="threadsCount">The number of threads to start</param>
        private void StartThreads(int threadsCount)
        {
            if (_stpStartInfo.StartSuspended)
            {
                return;
            }

            lock(_workerThreads.SyncRoot)
            {
                // Don't start threads on shut down
                if (_shutdown)
                {
                    return;
                }

                for(int i = 0; i < threadsCount; ++i)
                {
                    // Don't create more threads then the upper limit
                    if (_workerThreads.Count >= _stpStartInfo.MaxWorkerThreads)
                    {
                        return;
                    }

                    // Create a new thread
                    Thread workerThread;
                    if (_stpStartInfo.StackSize > 0)
                        workerThread = new Thread(ProcessQueuedItems, _stpStartInfo.StackSize);
                    else
                        workerThread = new Thread(ProcessQueuedItems);

                    // Configure the new thread and start it
                    workerThread.Name = "STP " + Name + " Thread #" + _threadCounter;
                    workerThread.IsBackground = true;
                    workerThread.Priority = _stpStartInfo.ThreadPriority;
                    workerThread.Start();
                    ++_threadCounter;

                    // Add the new thread to the hashtable and update its creation
                    // time.
                    _workerThreads[workerThread] = DateTime.Now;
                    _pcs.SampleThreads(_workerThreads.Count, _inUseWorkerThreads);
                }
            }
        }

        /// <summary>
        /// A worker thread method that processes work items from the work items queue.
        /// </summary>
        private void ProcessQueuedItems()
        {
            // Initialize the _smartThreadPool variable
            _smartThreadPool = this;

            try
            {
                bool bInUseWorkerThreadsWasIncremented = false;

                // Process until shutdown.
                while(!_shutdown)
                {
                    
                    // Wait for a work item, shutdown, or timeout
                    WorkItem workItem = Dequeue();

                    // On timeout or shut down.
                    if (null == workItem)
                    {
                        // Double lock for quit.
                        if (_workerThreads.Count > _stpStartInfo.MinWorkerThreads)
                        {
                            lock(_workerThreads.SyncRoot)
                            {
                                // Update the last time this thread was seen alive.
                                // It's good for debugging.
                                _workerThreads[Thread.CurrentThread] = DateTime.Now;

                                if (_workerThreads.Count > _stpStartInfo.MinWorkerThreads)
                                {
                                    // Inform that the thread is quiting and then quit.
                                    // This method must be called within this lock or else
                                    // more threads will quit and the thread pool will go
                                    // below the lower limit.
                                    InformCompleted();
                                    break;
                                }
                            }
                        }
                    }

                    // If we didn't quit then skip to the next iteration.
                    if (null == workItem)
                    {
                        continue;
                    }

                    try 
                    {
                        // Initialize the value to false
                        bInUseWorkerThreadsWasIncremented = false;

                        // Change the state of the work item to 'in progress' if possible.
                        // We do it here so if the work item has been canceled we won't 
                        // increment the _inUseWorkerThreads.
                        // The cancel mechanism doesn't delete items from the queue,  
                        // it marks the work item as canceled, and when the work item
                        // is dequeued, we just skip it.
                        // If the post execute of work item is set to always or to
                        // call when the work item is canceled then the StartingWorkItem()
                        // will return true, so the post execute can run.
                        if (!workItem.StartingWorkItem())
                        {
                            continue;
                        }

                        // Execute the callback.  Make sure to accurately
                        // record how many callbacks are currently executing.
                        int inUseWorkerThreads = Interlocked.Increment(ref _inUseWorkerThreads);
                        _pcs.SampleThreads(_workerThreads.Count, inUseWorkerThreads);

                        // Mark that the _inUseWorkerThreads incremented, so in the finally{}
                        // statement we will decrement it correctly.
                        bInUseWorkerThreadsWasIncremented = true;

                        // Set the _currentWorkItem to the current work item
                        _currentWorkItem = workItem;

                        lock(workItem)
                        {
                            workItem.currentThread = Thread.CurrentThread;
                        }

                        ExecuteWorkItem(workItem);

                        lock(workItem)
                        {
                            workItem.currentThread = null;
                        }

                    }
                    catch(ThreadAbortException ex)
                    {
                        lock(workItem)
                        {
                            workItem.currentThread = null;
                        }
                        ex.GetHashCode();
                        Thread.ResetAbort();
                    }
                    catch(Exception ex)
                    {
                        ex.GetHashCode();
                        // Do nothing
                    }
                    finally
                    {
                        lock(workItem)
                        {
                            workItem.currentThread = null;
                        }

                        if (null != workItem)
                        {
                            workItem.DisposeOfState();
                        }

                        // Set the _currentWorkItem to null, since we 
                        // no longer run user's code.
                        _currentWorkItem = null;

                        // Decrement the _inUseWorkerThreads only if we had 
                        // incremented it. Note the cancelled work items don't
                        // increment _inUseWorkerThreads.
                        if (bInUseWorkerThreadsWasIncremented)
                        {
                            int inUseWorkerThreads = Interlocked.Decrement(ref _inUseWorkerThreads);
                            _pcs.SampleThreads(_workerThreads.Count, inUseWorkerThreads);
                        }

                        // Notify that the work item has been completed.
                        // WorkItemsGroup may enqueue their next work item.
                        workItem.FireWorkItemCompleted();

                        // Decrement the number of work items here so the idle 
                        // ManualResetEvent won't fluctuate.
                        DecrementWorkItemsCount();
                    }
                }
            } 
            catch(ThreadAbortException tae)
            {
                tae.GetHashCode();
                // Handle the abort exception gracfully.
                Thread.ResetAbort();
            }
            catch(Exception e)
            {
                Debug.Assert(null != e);
            }
            finally
            {
                InformCompleted();
            }
        }

        private void ExecuteWorkItem(WorkItem workItem)
        {
            _pcs.SampleWorkItemsWaitTime(workItem.WaitingTime);
            try
            {
                workItem.Execute();
            }
            catch
            {
                throw;
            }
            finally
            {
                _pcs.SampleWorkItemsProcessTime(workItem.ProcessTime);
            }
        }


        #endregion

        #region Public Methods

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemCallback callback)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="workItemPriority">The priority of the work item</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemCallback callback, WorkItemPriority workItemPriority)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, workItemPriority);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="workItemInfo">Work item info</param>
        /// <param name="callback">A callback to execute</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemInfo workItemInfo, WorkItemCallback callback)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, workItemInfo, callback);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemCallback callback, object state)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <param name="workItemPriority">The work item priority</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemCallback callback, object state, WorkItemPriority workItemPriority)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state, workItemPriority);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="workItemInfo">Work item information</param>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(WorkItemInfo workItemInfo, WorkItemCallback callback, object state)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, workItemInfo, callback, state);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <param name="postExecuteWorkItemCallback">
        /// A delegate to call after the callback completion
        /// </param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(
            WorkItemCallback callback, 
            object state,
            PostExecuteWorkItemCallback postExecuteWorkItemCallback)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state, postExecuteWorkItemCallback);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <param name="postExecuteWorkItemCallback">
        /// A delegate to call after the callback completion
        /// </param>
        /// <param name="workItemPriority">The work item priority</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(
            WorkItemCallback callback, 
            object state,
            PostExecuteWorkItemCallback postExecuteWorkItemCallback,
            WorkItemPriority workItemPriority)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state, postExecuteWorkItemCallback, workItemPriority);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <param name="postExecuteWorkItemCallback">
        /// A delegate to call after the callback completion
        /// </param>
        /// <param name="callToPostExecute">Indicates on which cases to call to the post execute callback</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(
            WorkItemCallback callback, 
            object state,
            PostExecuteWorkItemCallback postExecuteWorkItemCallback,
            CallToPostExecute callToPostExecute)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state, postExecuteWorkItemCallback, callToPostExecute);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Queue a work item
        /// </summary>
        /// <param name="callback">A callback to execute</param>
        /// <param name="state">
        /// The context object of the work item. Used for passing arguments to the work item. 
        /// </param>
        /// <param name="postExecuteWorkItemCallback">
        /// A delegate to call after the callback completion
        /// </param>
        /// <param name="callToPostExecute">Indicates on which cases to call to the post execute callback</param>
        /// <param name="workItemPriority">The work item priority</param>
        /// <returns>Returns a work item result</returns>
        public IWorkItemResult QueueWorkItem(
            WorkItemCallback callback, 
            object state,
            PostExecuteWorkItemCallback postExecuteWorkItemCallback,
            CallToPostExecute callToPostExecute,
            WorkItemPriority workItemPriority)
        {
            ValidateNotDisposed();
            ValidateCallback(callback);
            WorkItem workItem = WorkItemFactory.CreateWorkItem(this, _stpStartInfo, callback, state, postExecuteWorkItemCallback, callToPostExecute, workItemPriority);
            Enqueue(workItem);
            return workItem.GetWorkItemResult();
        }

        /// <summary>
        /// Wait for the thread pool to be idle
        /// </summary>
        public void WaitForIdle()
        {
            WaitForIdle(Timeout.Infinite);
        }

        /// <summary>
        /// Wait for the thread pool to be idle
        /// </summary>
        public bool WaitForIdle(TimeSpan timeout)
        {
            return WaitForIdle((int)timeout.TotalMilliseconds);
        }

        /// <summary>
        /// Wait for the thread pool to be idle
        /// </summary>
        public bool WaitForIdle(int millisecondsTimeout)
        {
            ValidateWaitForIdle();
            return _isIdleWaitHandle.WaitOne(millisecondsTimeout, false);
        }

        private void ValidateWaitForIdle()
        {
            if(_smartThreadPool == this)
            {
                throw new NotSupportedException(
                    "WaitForIdle cannot be called from a thread on its SmartThreadPool, it will cause may cause a deadlock");
            }
        }

        internal void ValidateWorkItemsGroupWaitForIdle(IWorkItemsGroup workItemsGroup)
        {
            ValidateWorkItemsGroupWaitForIdleImpl(workItemsGroup, SmartThreadPool._currentWorkItem);
            if ((null != workItemsGroup) && 
                (null != SmartThreadPool._currentWorkItem) &&
                SmartThreadPool._currentWorkItem.WasQueuedBy(workItemsGroup))
            {
                throw new NotSupportedException("WaitForIdle cannot be called from a thread on its SmartThreadPool, it will cause may cause a deadlock");
            }
        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        private void ValidateWorkItemsGroupWaitForIdleImpl(IWorkItemsGroup workItemsGroup, WorkItem workItem)
        {
            if ((null != workItemsGroup) && 
                (null != workItem) &&
                workItem.WasQueuedBy(workItemsGroup))
            {
                throw new NotSupportedException("WaitForIdle cannot be called from a thread on its SmartThreadPool, it will cause may cause a deadlock");
            }
        }



        /// <summary>
        /// Force the SmartThreadPool to shutdown
        /// </summary>
        public void Shutdown()
        {
            Shutdown(true, 0);
        }

        public void Shutdown(bool forceAbort, TimeSpan timeout)
        {
            Shutdown(forceAbort, (int)timeout.TotalMilliseconds);
        }

        /// <summary>
        /// Empties the queue of work items and abort the threads in the pool.
        /// </summary>
        public void Shutdown(bool forceAbort, int millisecondsTimeout)
        {
            ValidateNotDisposed();

            ISTPInstancePerformanceCounters pcs = _pcs;

            if (NullSTPInstancePerformanceCounters.Instance != _pcs)
            {
                _pcs.Dispose();
                // Set the _pcs to "null" to stop updating the performance
                // counters
                _pcs = NullSTPInstancePerformanceCounters.Instance;
            }

            Thread [] threads = null;
            lock(_workerThreads.SyncRoot)
            {
                // Shutdown the work items queue
                _workItemsQueue.Dispose();

                // Signal the threads to exit
                _shutdown = true;
                _shuttingDownEvent.Set();

                // Make a copy of the threads' references in the pool
                threads = new Thread [_workerThreads.Count];
                _workerThreads.Keys.CopyTo(threads, 0);
            }

            int millisecondsLeft = millisecondsTimeout;
            DateTime start = DateTime.Now;
            bool waitInfinitely = (Timeout.Infinite == millisecondsTimeout);
            bool timeout = false;

            // Each iteration we update the time left for the timeout.
            foreach(Thread thread in threads)
            {
                // Join don't work with negative numbers
                if (!waitInfinitely && (millisecondsLeft < 0))
                {
                    timeout = true;
                    break;
                }

                // Wait for the thread to terminate
                bool success = thread.Join(millisecondsLeft);
                if(!success)
                {
                    timeout = true;
                    break;
                }

                if(!waitInfinitely)
                {
                    // Update the time left to wait
                    TimeSpan ts = DateTime.Now - start;
                    millisecondsLeft = millisecondsTimeout - (int)ts.TotalMilliseconds;
                }
            }

            if (timeout && forceAbort)
            {
                // Abort the threads in the pool
                foreach(Thread thread in threads)
                {
                    if ((thread != null) && thread.IsAlive) 
                    {
                        try 
                        {
                            thread.Abort("Shutdown");
                        }
                        catch(SecurityException e)
                        {
                            e.GetHashCode();
                        }
                        catch(ThreadStateException ex)
                        {
                            ex.GetHashCode();
                            // In case the thread has been terminated 
                            // after the check if it is alive.
                        }
                    }
                }
            }

            // Dispose of the performance counters
            pcs.Dispose();
        }

        /// <summary>
        /// Wait for all work items to complete
        /// </summary>
        /// <param name="workItemResults">Array of work item result objects</param>
        /// <returns>
        /// true when every work item in workItemResults has completed; otherwise false.
        /// </returns>
        public static bool WaitAll(
            IWorkItemResult [] workItemResults)
        {
            return WaitAll(workItemResults, Timeout.Infinite, true);
        }

        /// <summary>
        /// Wait for all work items to complete
        /// </summary>
        /// <param name="workItemResults">Array of work item result objects</param>
        /// <param name="timeout">The number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds 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>
        /// <returns>
        /// true when every work item in workItemResults has completed; otherwise false.
        /// </returns>
        public static bool WaitAll(
            IWorkItemResult [] workItemResults,
            TimeSpan timeout,
            bool exitContext)
        {
            return WaitAll(workItemResults, (int)timeout.TotalMilliseconds, exitContext);
        }

        /// <summary>
        /// Wait for all work items to complete
        /// </summary>
        /// <param name="workItemResults">Array of work item result objects</param>
        /// <param name="timeout">The number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds 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.
        /// </returns>
        public static bool WaitAll(
            IWorkItemResult [] workItemResults,  
            TimeSpan timeout,
            bool exitContext,
            WaitHandle cancelWaitHandle)
        {
            return WaitAll(workItemResults, (int)timeout.TotalMilliseconds, exitContext, cancelWaitHandle);
        }

        /// <summary>
        /// Wait for all work items to complete
        /// </summary>
        /// <param name="workItemResults">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>
        /// <returns>
        /// true when every work item in workItemResults has completed; otherwise false.
        /// </returns>
        public static bool WaitAll(
            IWorkItemResult [] workItemResults,  
            int millisecondsTimeout,
            bool exitContext)
        {
            return WorkItem.WaitAll(workItemResults, millisecondsTimeout, exitContext, null);
        }

        /// <summary>
        /// Wait for all work items to complete
        /// </summary>
        /// <param name="workItemResults">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.
        /// </returns>
        public static bool WaitAll(
            IWorkItemResult [] workItemResults,  
            int millisecondsTimeout,
            bool exitContext,
            WaitHandle cancelWaitHandle)
        {
            return WorkItem.WaitAll(workItemResults, millisecondsTimeout, exitContext, cancelWaitHandle);
        }


        /// <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>
        /// <returns>
        /// The array index of the work item result that satisfied the wait, or WaitTimeout if any of the work items has been canceled.
        /// </returns>
        public static int WaitAny(
            IWorkItemResult [] workItemResults)
        {
            return WaitAny(workItemResults, Timeout.Infinite, true);
        }

        /// <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="timeout">The number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds 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>
        /// <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>
        public static int WaitAny(
            IWorkItemResult [] workItemResults,
            TimeSpan timeout,
            bool exitContext)
        {
            return WaitAny(workItemResults, (int)timeout.TotalMilliseconds, exitContext);
        }

        /// <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="timeout">The number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds 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>
        /// 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>
        public static int WaitAny(
            IWorkItemResult [] workItemResults,
            TimeSpan timeout,
            bool exitContext,
            WaitHandle cancelWaitHandle)
        {
            return WaitAny(workItemResults, (int)timeout.TotalMilliseconds, exitContext, cancelWaitHandle);
        }

        /// <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="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>
        /// <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>
        public static int WaitAny(
            IWorkItemResult [] workItemResults,  
            int millisecondsTimeout,
            bool exitContext)
        {
            return WorkItem.WaitAny(workItemResults, millisecondsTimeout, exitContext, null);
        }

        /// <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="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>
        /// 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>
        public static int WaitAny(
            IWorkItemResult [] workItemResults,  
            int millisecondsTimeout,
            bool exitContext,
            WaitHandle cancelWaitHandle)
        {
            return WorkItem.WaitAny(workItemResults, millisecondsTimeout, exitContext, cancelWaitHandle);
        }

        public IWorkItemsGroup CreateWorkItemsGroup(int concurrency)
        {
            IWorkItemsGroup workItemsGroup = new WorkItemsGroup(this, concurrency, _stpStartInfo);
            return workItemsGroup;
        }

        public IWorkItemsGroup CreateWorkItemsGroup(int concurrency, WIGStartInfo wigStartInfo)
        {
            IWorkItemsGroup workItemsGroup = new WorkItemsGroup(this, concurrency, wigStartInfo);
            return workItemsGroup;
        }

        public event WorkItemsGroupIdleHandler OnIdle
        {
            add
            {
                throw new NotImplementedException("This event is not implemented in the SmartThreadPool class. Please create a WorkItemsGroup in order to use this feature.");
                //_onIdle += value;
            }
            remove
            {
                throw new NotImplementedException("This event is not implemented in the SmartThreadPool class. Please create a WorkItemsGroup in order to use this feature.");
                //_onIdle -= value;
            }
        }

        public void Cancel()
        {
            ICollection workItemsGroups = _workItemsGroups.Values;
            foreach(WorkItemsGroup workItemsGroup in workItemsGroups)
            {
                workItemsGroup.Cancel();
            }
        }

        public void Start()
        {
            lock (this)
            {
                if (!this._stpStartInfo.StartSuspended)
                {
                    return;
                }
                _stpStartInfo.StartSuspended = false;
            }
            
            ICollection workItemsGroups = _workItemsGroups.Values;
            foreach(WorkItemsGroup workItemsGroup in workItemsGroups)
            {
                workItemsGroup.OnSTPIsStarting();
            }

            StartOptimalNumberOfThreads();
        }

        #endregion

        #region Properties

        /// <summary>
        /// Get/Set the name of the SmartThreadPool instance
        /// </summary>
        public string Name 
        { 
            get
            {
                return _name;
            }

            set
            {
                _name = value;
            }
        }

        /// <summary>
        /// Get the lower limit of threads in the pool.
        /// </summary>
        public int MinThreads 
        { 
            get 
            {
                ValidateNotDisposed();
                return _stpStartInfo.MinWorkerThreads; 
            }
        }

        /// <summary>
        /// Get the upper limit of threads in the pool.
        /// </summary>
        public int MaxThreads 
        { 
            get 
            {
                ValidateNotDisposed();
                return _stpStartInfo.MaxWorkerThreads; 
            } 
        }
        /// <summary>
        /// Get the number of threads in the thread pool.
        /// Should be between the lower and the upper limits.
        /// </summary>
        public int ActiveThreads 
        { 
            get 
            {
                ValidateNotDisposed();
                return _workerThreads.Count; 
            } 
        }

        /// <summary>
        /// Get the number of busy (not idle) threads in the thread pool.
        /// </summary>
        public int InUseThreads 
        { 
            get 
            { 
                ValidateNotDisposed();
                return _inUseWorkerThreads; 
            } 
        }

        /// <summary>
        /// Get the number of work items in the queue.
        /// </summary>
        public int WaitingCallbacks 
        { 
            get 
            { 
                ValidateNotDisposed();
                return _workItemsQueue.Count;
            } 
        }


        public event EventHandler Idle
        {
            add
            {
                _stpIdle += value;
            }

            remove
            {
                _stpIdle -= value;
            }
        }

        #endregion

        #region IDisposable Members

//        ~SmartThreadPool()
//        {
//            Dispose();
//        }

        public void Dispose()
        {
            if (!_isDisposed)
            {
                if (!_shutdown)
                {
                    Shutdown();
                }

                if (null != _shuttingDownEvent)
                {
                    _shuttingDownEvent.Close();
                    _shuttingDownEvent = null;
                }
                _workerThreads.Clear();
                _isDisposed = true;
                GC.SuppressFinalize(this);
            }
        }

        private void ValidateNotDisposed()
        {
            if(_isDisposed)
            {
                throw new ObjectDisposedException(GetType().ToString(), "The SmartThreadPool has been shutdown");
            }
        }
        #endregion
    }
    #endregion
}