mcs/class/corlib/System.Threading.Tasks/Task.cs

   1 //
   2 // Task.cs
   3 //
   4 // Authors:
   5 //    Marek Safar  <marek.safar@gmail.com>
   6 //    Jérémie Laval <jeremie dot laval at xamarin dot com>
   7 //
   8 // Copyright (c) 2008 Jérémie "Garuma" Laval
   9 // Copyright 2011-2013 Xamarin Inc (http://www.xamarin.com).
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining a copy
  12 // of this software and associated documentation files (the "Software"), to deal
  13 // in the Software without restriction, including without limitation the rights
  14 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  15 // copies of the Software, and to permit persons to whom the Software is
  16 // furnished to do so, subject to the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be included in
  19 // all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  22 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  23 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  24 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  25 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  26 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  27 // THE SOFTWARE.
  28 //
  29 //
  30
  31 #if NET_4_0
  32
  33 using System;
  34 using System.Threading;
  35 using System.Collections.Concurrent;
  36 using System.Collections.Generic;
  37 using System.Runtime.CompilerServices;
  38
  39 namespace System.Threading.Tasks
  40 {
  41         [System.Diagnostics.DebuggerDisplay ("Id = {Id}, Status = {Status}")]
  42         [System.Diagnostics.DebuggerTypeProxy (typeof (TaskDebuggerView))]
  43         public class Task : IDisposable, IAsyncResult
  44         {
  45                 // With this attribute each thread has its own value so that it's correct for our Schedule code
  46                 // and for Parent property.
  47                 [System.ThreadStatic]
  48                 static Task current;
  49
  50                 // parent is the outer task in which this task is created
  51                 Task parent;
  52                 // A reference to a Task on which this continuation is attached to
  53                 Task contAncestor;
  54
  55                 static int          id = -1;
  56                 static readonly TaskFactory defaultFactory = new TaskFactory ();
  57
  58                 CountdownEvent childTasks;
  59
  60                 int                 taskId;
  61                 TaskCreationOptions creationOptions;
  62
  63                 internal TaskScheduler       scheduler;
  64
  65                 TaskExceptionSlot exSlot;
  66                 ManualResetEvent wait_handle;
  67
  68                 TaskStatus          status;
  69
  70                 TaskActionInvoker invoker;
  71                 object         state;
  72                 internal AtomicBooleanValue executing;
  73
  74                 TaskCompletionQueue<IContinuation> continuations;
  75
  76                 CancellationToken token;
  77                 CancellationTokenRegistration? cancellationRegistration;
  78
  79                 ExecutionContext ec;
  80
  81                 internal const TaskCreationOptions WorkerTaskNotSupportedOptions = TaskCreationOptions.LongRunning | TaskCreationOptions.PreferFairness;
  82
  83                 const TaskCreationOptions MaxTaskCreationOptions =
  84 #if NET_4_5
  85                         TaskCreationOptions.DenyChildAttach | TaskCreationOptions.HideScheduler |
  86 #endif
  87                         TaskCreationOptions.PreferFairness | TaskCreationOptions.LongRunning | TaskCreationOptions.AttachedToParent;
  88
  89                 public Task (Action action)
  90                         : this (action, TaskCreationOptions.None)
  91                 {
  92
  93                 }
  94
  95                 public Task (Action action, TaskCreationOptions creationOptions)
  96                         : this (action, CancellationToken.None, creationOptions)
  97                 {
  98
  99                 }
 100
 101                 public Task (Action action, CancellationToken cancellationToken)
 102                         : this (action, cancellationToken, TaskCreationOptions.None)
 103                 {
 104
 105                 }
 106
 107                 public Task (Action action, CancellationToken cancellationToken, TaskCreationOptions creationOptions)
 108                         : this (TaskActionInvoker.Create (action), null, cancellationToken, creationOptions, current)
 109                 {
 110                         if (action == null)
 111                                 throw new ArgumentNullException ("action");
 112                         if (creationOptions > MaxTaskCreationOptions || creationOptions < TaskCreationOptions.None)
 113                                 throw new ArgumentOutOfRangeException ("creationOptions");
 114                 }
 115
 116                 public Task (Action<object> action, object state)
 117                         : this (action, state, TaskCreationOptions.None)
 118                 {
 119                 }
 120
 121                 public Task (Action<object> action, object state, TaskCreationOptions creationOptions)
 122                         : this (action, state, CancellationToken.None, creationOptions)
 123                 {
 124                 }
 125
 126                 public Task (Action<object> action, object state, CancellationToken cancellationToken)
 127                         : this (action, state, cancellationToken, TaskCreationOptions.None)
 128                 {
 129                 }
 130
 131                 public Task (Action<object> action, object state, CancellationToken cancellationToken, TaskCreationOptions creationOptions)
 132                         : this (TaskActionInvoker.Create (action), state, cancellationToken, creationOptions, current)
 133                 {
 134                         if (action == null)
 135                                 throw new ArgumentNullException ("action");
 136                         if (creationOptions > MaxTaskCreationOptions || creationOptions < TaskCreationOptions.None)
 137                                 throw new ArgumentOutOfRangeException ("creationOptions");
 138                 }
 139
 140                 internal Task (TaskActionInvoker invoker, object state, CancellationToken cancellationToken,
 141                                TaskCreationOptions creationOptions, Task parent = null, Task contAncestor = null, bool ignoreCancellation = false)
 142                 {
 143                         this.invoker         = invoker;
 144                         this.creationOptions = creationOptions;
 145                         this.state           = state;
 146                         this.taskId          = Interlocked.Increment (ref id);
 147                         this.token           = cancellationToken;
 148                         this.parent          = parent = parent == null ? current : parent;
 149                         this.contAncestor    = contAncestor;
 150                         this.status          = cancellationToken.IsCancellationRequested && !ignoreCancellation ? TaskStatus.Canceled : TaskStatus.Created;
 151
 152                         // Process creationOptions
 153 #if NET_4_5
 154                         if (parent != null && HasFlag (creationOptions, TaskCreationOptions.AttachedToParent)
 155                             && !HasFlag (parent.CreationOptions, TaskCreationOptions.DenyChildAttach))
 156 #else
 157                         if (parent != null && HasFlag (creationOptions, TaskCreationOptions.AttachedToParent))
 158 #endif
 159                                 parent.AddChild ();
 160
 161                         if (token.CanBeCanceled && !ignoreCancellation)
 162                                 cancellationRegistration = token.Register (l => ((Task) l).CancelReal (), this);
 163
 164                         ec = ExecutionContext.Capture (false, true);
 165                 }
 166
 167                 static bool HasFlag (TaskCreationOptions opt, TaskCreationOptions member)
 168                 {
 169                         return (opt & member) == member;
 170                 }
 171
 172                 #region Start
 173                 public void Start ()
 174                 {
 175                         Start (TaskScheduler.Current);
 176                 }
 177
 178                 public void Start (TaskScheduler scheduler)
 179                 {
 180                         if (scheduler == null)
 181                                 throw new ArgumentNullException ("scheduler");
 182
 183                         if (status >= TaskStatus.WaitingToRun)
 184                                 throw new InvalidOperationException ("The Task is not in a valid state to be started.");
 185
 186                         if (IsContinuation)
 187                                 throw new InvalidOperationException ("Start may not be called on a continuation task");
 188
 189                         if (IsPromise)
 190                                 throw new InvalidOperationException ("Start may not be called on a promise-style task");
 191
 192                         SetupScheduler (scheduler);
 193                         Schedule (true);
 194                 }
 195
 196                 internal void SetupScheduler (TaskScheduler scheduler)
 197                 {
 198                         this.scheduler = scheduler;
 199                         Status = TaskStatus.WaitingForActivation;
 200                 }
 201
 202                 public void RunSynchronously ()
 203                 {
 204                         RunSynchronously (TaskScheduler.Current);
 205                 }
 206
 207                 public void RunSynchronously (TaskScheduler scheduler)
 208                 {
 209                         if (scheduler == null)
 210                                 throw new ArgumentNullException ("scheduler");
 211
 212                         if (Status > TaskStatus.WaitingForActivation)
 213                                 throw new InvalidOperationException ("The task is not in a valid state to be started");
 214
 215                         if (IsContinuation)
 216                                 throw new InvalidOperationException ("RunSynchronously may not be called on a continuation task");
 217
 218                         if (IsPromise)
 219                                 throw new InvalidOperationException ("RunSynchronously may not be called on a promise-style task");
 220
 221                         RunSynchronouslyCore (scheduler, true);
 222                 }
 223
 224                 internal void RunSynchronouslyCore (TaskScheduler scheduler, bool throwException)
 225                 {
 226                         SetupScheduler (scheduler);
 227                         Status = TaskStatus.WaitingToRun;
 228
 229                         try {
 230                                 if (scheduler.RunInline (this, false))
 231                                         return;
 232                         } catch (Exception inner) {
 233                                 var ex = new TaskSchedulerException (inner);
 234                                 TrySetException (new AggregateException (ex), false, true);
 235                                 if (throwException)
 236                                         throw ex;
 237
 238                                 return;
 239                         }
 240
 241                         Schedule (throwException);
 242                         WaitCore (Timeout.Infinite, CancellationToken.None, false);
 243                 }
 244                 #endregion
 245
 246                 #region ContinueWith
 247                 public Task ContinueWith (Action<Task> continuationAction)
 248                 {
 249                         return ContinueWith (continuationAction, TaskContinuationOptions.None);
 250                 }
 251
 252                 public Task ContinueWith (Action<Task> continuationAction, TaskContinuationOptions continuationOptions)
 253                 {
 254                         return ContinueWith (continuationAction, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 255                 }
 256
 257                 public Task ContinueWith (Action<Task> continuationAction, CancellationToken cancellationToken)
 258                 {
 259                         return ContinueWith (continuationAction, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 260                 }
 261
 262                 public Task ContinueWith (Action<Task> continuationAction, TaskScheduler scheduler)
 263                 {
 264                         return ContinueWith (continuationAction, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 265                 }
 266
 267                 public Task ContinueWith (Action<Task> continuationAction, CancellationToken cancellationToken, TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 268                 {
 269                         if (continuationAction == null)
 270                                 throw new ArgumentNullException ("continuationAction");
 271                         if (scheduler == null)
 272                                 throw new ArgumentNullException ("scheduler");
 273
 274                         return ContinueWith (TaskActionInvoker.Create (continuationAction), cancellationToken, continuationOptions, scheduler);
 275                 }
 276
 277                 internal Task ContinueWith (TaskActionInvoker invoker, CancellationToken cancellationToken, TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 278                 {
 279                         var lazyCancellation = false;
 280 #if NET_4_5
 281                         lazyCancellation = (continuationOptions & TaskContinuationOptions.LazyCancellation) > 0;
 282 #endif
 283                         var continuation = new Task (invoker, null, cancellationToken, GetCreationOptions (continuationOptions), null, this, lazyCancellation);
 284                         ContinueWithCore (continuation, continuationOptions, scheduler);
 285
 286                         return continuation;
 287                 }
 288
 289                 public Task<TResult> ContinueWith<TResult> (Func<Task, TResult> continuationFunction)
 290                 {
 291                         return ContinueWith<TResult> (continuationFunction, TaskContinuationOptions.None);
 292                 }
 293
 294                 public Task<TResult> ContinueWith<TResult> (Func<Task, TResult> continuationFunction, TaskContinuationOptions continuationOptions)
 295                 {
 296                         return ContinueWith<TResult> (continuationFunction, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 297                 }
 298
 299                 public Task<TResult> ContinueWith<TResult> (Func<Task, TResult> continuationFunction, CancellationToken cancellationToken)
 300                 {
 301                         return ContinueWith<TResult> (continuationFunction, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 302                 }
 303
 304                 public Task<TResult> ContinueWith<TResult> (Func<Task, TResult> continuationFunction, TaskScheduler scheduler)
 305                 {
 306                         return ContinueWith<TResult> (continuationFunction, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 307                 }
 308
 309                 public Task<TResult> ContinueWith<TResult> (Func<Task, TResult> continuationFunction, CancellationToken cancellationToken,
 310                                                             TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 311                 {
 312                         if (continuationFunction == null)
 313                                 throw new ArgumentNullException ("continuationFunction");
 314                         if (scheduler == null)
 315                                 throw new ArgumentNullException ("scheduler");
 316
 317                         return ContinueWith<TResult> (TaskActionInvoker.Create (continuationFunction), cancellationToken, continuationOptions, scheduler);
 318                 }
 319
 320                 internal Task<TResult> ContinueWith<TResult> (TaskActionInvoker invoker, CancellationToken cancellationToken, TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 321                 {
 322                         var lazyCancellation = false;
 323 #if NET_4_5
 324                         lazyCancellation = (continuationOptions & TaskContinuationOptions.LazyCancellation) > 0;
 325 #endif
 326                         var continuation = new Task<TResult> (invoker, null, cancellationToken, GetCreationOptions (continuationOptions), parent, this, lazyCancellation);
 327                         ContinueWithCore (continuation, continuationOptions, scheduler);
 328
 329                         return continuation;
 330                 }
 331
 332                 internal void ContinueWithCore (Task continuation, TaskContinuationOptions options, TaskScheduler scheduler)
 333                 {
 334                         const TaskContinuationOptions wrongRan = TaskContinuationOptions.NotOnRanToCompletion | TaskContinuationOptions.OnlyOnRanToCompletion;
 335                         const TaskContinuationOptions wrongCanceled = TaskContinuationOptions.NotOnCanceled | TaskContinuationOptions.OnlyOnCanceled;
 336                         const TaskContinuationOptions wrongFaulted = TaskContinuationOptions.NotOnFaulted | TaskContinuationOptions.OnlyOnFaulted;
 337
 338                         if (((options & wrongRan) == wrongRan) || ((options & wrongCanceled) == wrongCanceled) || ((options & wrongFaulted) == wrongFaulted))
 339                                 throw new ArgumentException ("continuationOptions", "Some options are mutually exclusive");
 340
 341                         // Already set the scheduler so that user can call Wait and that sort of stuff
 342                         continuation.scheduler = scheduler;
 343                         continuation.Status = TaskStatus.WaitingForActivation;
 344
 345                         ContinueWith (new TaskContinuation (continuation, options));
 346                 }
 347
 348                 internal bool ContinueWith (IContinuation continuation, bool canExecuteInline = true)
 349                 {
 350                         if (IsCompleted) {
 351                                 if (!canExecuteInline)
 352                                         return false;
 353
 354                                 continuation.Execute ();
 355                                 return true;
 356                         }
 357
 358                         continuations.Add (continuation);
 359
 360                         // Retry in case completion was achieved but event adding was too late
 361                         if (IsCompleted && continuations.Remove (continuation)) {
 362                                 if (!canExecuteInline)
 363                                         return false;
 364
 365                                 continuation.Execute ();
 366                         }
 367
 368                         return true;
 369                 }
 370
 371                 internal void RemoveContinuation (IContinuation continuation)
 372                 {
 373                         continuations.Remove (continuation);
 374                 }
 375
 376                 static internal TaskCreationOptions GetCreationOptions (TaskContinuationOptions kind)
 377                 {
 378                         TaskCreationOptions options = TaskCreationOptions.None;
 379                         if ((kind & TaskContinuationOptions.AttachedToParent) > 0)
 380                                 options |= TaskCreationOptions.AttachedToParent;
 381                         if ((kind & TaskContinuationOptions.PreferFairness) > 0)
 382                                 options |= TaskCreationOptions.PreferFairness;
 383                         if ((kind & TaskContinuationOptions.LongRunning) > 0)
 384                                 options |= TaskCreationOptions.LongRunning;
 385
 386                         return options;
 387                 }
 388                 #endregion
 389
 390                 #region Internal and protected thingies
 391                 internal void Schedule (bool throwException)
 392                 {
 393                         Status = TaskStatus.WaitingToRun;
 394                         try {
 395                                 scheduler.QueueTask (this);
 396                         } catch (Exception inner) {
 397                                 var ex = new TaskSchedulerException (inner);
 398                                 TrySetException (new AggregateException (ex), false, true);
 399                                 if (throwException)
 400                                         throw ex;
 401                         }
 402                 }
 403
 404                 void ThreadStart ()
 405                 {
 406                         /* Allow scheduler to break fairness of deque ordering without
 407                          * breaking its semantic (the task can be executed twice but the
 408                          * second time it will return immediately
 409                          */
 410                         if (!executing.TryRelaxedSet ())
 411                                 return;
 412
 413                         // Disable CancellationToken direct cancellation
 414                         if (cancellationRegistration != null) {
 415                                 cancellationRegistration.Value.Dispose ();
 416                                 cancellationRegistration = null;
 417                         }
 418
 419                         // If Task are ran inline on the same thread we might trash these values
 420                         var saveCurrent = current;
 421                         var saveScheduler = TaskScheduler.Current;
 422
 423                         current = this;
 424 #if NET_4_5
 425                         TaskScheduler.Current = HasFlag (creationOptions, TaskCreationOptions.HideScheduler) ? TaskScheduler.Default : scheduler;
 426 #else
 427                         TaskScheduler.Current = scheduler;
 428 #endif
 429
 430                         if (!token.IsCancellationRequested) {
 431
 432                                 status = TaskStatus.Running;
 433
 434                                 try {
 435                                         if (ec != null)
 436                                                 ExecutionContext.Run (ec, l => ((Task) l).InnerInvoke (), this);
 437                                         else
 438                                                 InnerInvoke ();
 439                                 } catch (OperationCanceledException oce) {
 440                                         if (token != CancellationToken.None && oce.CancellationToken == token)
 441                                                 CancelReal ();
 442                                         else
 443                                                 HandleGenericException (oce);
 444                                 } catch (Exception e) {
 445                                         HandleGenericException (e);
 446                                 }
 447                         } else {
 448                                 CancelReal ();
 449                         }
 450
 451                         if (saveCurrent != null)
 452                                 current = saveCurrent;
 453                         if (saveScheduler != null)
 454                                 TaskScheduler.Current = saveScheduler;
 455                         Finish ();
 456                 }
 457
 458                 internal bool TrySetCanceled ()
 459                 {
 460                         if (IsCompleted)
 461                                 return false;
 462
 463                         if (!executing.TryRelaxedSet ()) {
 464                                 var sw = new SpinWait ();
 465                                 while (!IsCompleted)
 466                                         sw.SpinOnce ();
 467
 468                                 return false;
 469                         }
 470
 471                         CancelReal ();
 472                         return true;
 473                 }
 474
 475                 internal bool TrySetException (AggregateException aggregate, bool cancellation, bool observed)
 476                 {
 477                         if (IsCompleted)
 478                                 return false;
 479
 480                         if (!executing.TryRelaxedSet ()) {
 481                                 var sw = new SpinWait ();
 482                                 while (!IsCompleted)
 483                                         sw.SpinOnce ();
 484
 485                                 return false;
 486                         }
 487
 488                         if (cancellation) {
 489                                 ExceptionSlot.SetException (aggregate);
 490                                 CancelReal ();
 491                         } else {
 492                                 HandleGenericException (aggregate);
 493                         }
 494
 495                         if (observed)
 496                                 exSlot.Observed = true;
 497
 498                         return true;
 499                 }
 500
 501                 internal bool TrySetExceptionObserved ()
 502                 {
 503                         if (exSlot != null) {
 504                                 exSlot.Observed = true;
 505                                 return true;
 506                         }
 507                         return false;
 508                 }
 509
 510                 internal void Execute ()
 511                 {
 512                         ThreadStart ();
 513                 }
 514
 515                 internal void AddChild ()
 516                 {
 517                         if (childTasks == null)
 518                                 Interlocked.CompareExchange (ref childTasks, new CountdownEvent (1), null);
 519                         childTasks.AddCount ();
 520                 }
 521
 522                 internal void ChildCompleted (AggregateException childEx)
 523                 {
 524                         if (childEx != null) {
 525                                 if (ExceptionSlot.ChildExceptions == null)
 526                                         Interlocked.CompareExchange (ref ExceptionSlot.ChildExceptions, new ConcurrentQueue<AggregateException> (), null);
 527                                 ExceptionSlot.ChildExceptions.Enqueue (childEx);
 528                         }
 529
 530                         if (childTasks.Signal () && status == TaskStatus.WaitingForChildrenToComplete) {
 531                                 ProcessChildExceptions ();
 532                                 Status = exSlot == null ? TaskStatus.RanToCompletion : TaskStatus.Faulted;
 533                                 ProcessCompleteDelegates ();
 534                                 if (parent != null && NotifyParentOnFinish ())
 535                                         parent = null;
 536                         }
 537                 }
 538
 539                 void InnerInvoke ()
 540                 {
 541                         if (IsContinuation) {
 542                                 var ancestor = contAncestor;
 543                                 contAncestor = null;
 544                                 invoker.Invoke (ancestor, state, this);
 545                         } else {
 546                                 invoker.Invoke (this, state, this);
 547                         }
 548                 }
 549
 550                 internal void Finish ()
 551                 {
 552                         // If there was children created and they all finished, we set the countdown
 553                         if (childTasks != null) {
 554                                 if (childTasks.Signal ())
 555                                         ProcessChildExceptions (true);
 556                         }
 557
 558                         // Don't override Canceled or Faulted
 559                         if (status == TaskStatus.Running) {
 560                                 if (childTasks == null || childTasks.IsSet)
 561                                         Status = TaskStatus.RanToCompletion;
 562                                 else
 563                                         Status = TaskStatus.WaitingForChildrenToComplete;
 564                         }
 565
 566                         if (wait_handle != null)
 567                                 wait_handle.Set ();
 568
 569                         // Tell parent that we are finished
 570                         if (parent != null && NotifyParentOnFinish ()) {
 571                                 //
 572                                 // Break the reference back to the parent, otherwise any Tasks created from another Task's thread of
 573                                 // execution will create an undesired linked-list that the GC cannot free. See bug #18398.
 574                                 //
 575                                 parent = null;
 576                         }
 577
 578                         // Completions are already processed when task is canceled or faulted
 579                         if (status == TaskStatus.RanToCompletion)
 580                                 ProcessCompleteDelegates ();
 581
 582                         // Reset the current thingies
 583                         if (current == this)
 584                                 current = null;
 585                         if (TaskScheduler.Current == scheduler)
 586                                 TaskScheduler.Current = null;
 587
 588                         if (cancellationRegistration.HasValue)
 589                                 cancellationRegistration.Value.Dispose ();
 590                 }
 591
 592                 bool NotifyParentOnFinish ()
 593                 {
 594                         if (!HasFlag (creationOptions, TaskCreationOptions.AttachedToParent))
 595                                 return true;
 596 #if NET_4_5
 597                         if (HasFlag (parent.CreationOptions, TaskCreationOptions.DenyChildAttach))
 598                                 return true;
 599 #endif
 600                         if (status != TaskStatus.WaitingForChildrenToComplete)
 601                                 parent.ChildCompleted (Exception);
 602
 603                         return false;
 604                 }
 605
 606                 void ProcessCompleteDelegates ()
 607                 {
 608                         if (continuations.HasElements) {
 609                                 IContinuation continuation;
 610                                 while (continuations.TryGetNextCompletion (out continuation))
 611                                         continuation.Execute ();
 612                         }
 613                 }
 614
 615                 void ProcessChildExceptions (bool isParent = false)
 616                 {
 617                         if (exSlot == null || exSlot.ChildExceptions == null)
 618                                 return;
 619
 620                         var exceptions = new List<Exception> ();
 621                         if (exSlot.Exception != null)
 622                                 exceptions.AddRange (exSlot.Exception.InnerExceptions);
 623
 624                         AggregateException childEx;
 625                         while (exSlot.ChildExceptions.TryDequeue (out childEx))
 626                                 exceptions.Add (childEx);
 627
 628                         exSlot.SetException (new AggregateException (exceptions));
 629
 630                         if (isParent) {
 631                                 Status = TaskStatus.Faulted;
 632                                 ProcessCompleteDelegates ();
 633                         }
 634                 }
 635                 #endregion
 636
 637                 #region Cancel and Wait related method
 638
 639                 internal void CancelReal (bool notifyParent = false)
 640                 {
 641                         Status = TaskStatus.Canceled;
 642
 643                         if (wait_handle != null)
 644                                 wait_handle.Set ();
 645
 646                         ProcessCompleteDelegates ();
 647
 648                         if (notifyParent && parent != null && NotifyParentOnFinish ())
 649                                 parent = null;
 650                 }
 651
 652                 void HandleGenericException (Exception e)
 653                 {
 654                         HandleGenericException (new AggregateException (e));
 655                 }
 656
 657                 void HandleGenericException (AggregateException e)
 658                 {
 659                         ExceptionSlot.SetException (e);
 660                         Thread.MemoryBarrier ();
 661                         Status = TaskStatus.Faulted;
 662
 663                         if (wait_handle != null)
 664                                 wait_handle.Set ();
 665
 666                         ProcessCompleteDelegates ();
 667                 }
 668
 669                 internal bool WaitOnChildren ()
 670                 {
 671                         if (Status == TaskStatus.WaitingForChildrenToComplete && childTasks != null) {
 672                                 childTasks.Wait ();
 673                                 return true;
 674                         }
 675                         return false;
 676                 }
 677
 678                 public void Wait ()
 679                 {
 680                         Wait (Timeout.Infinite, CancellationToken.None);
 681                 }
 682
 683                 public void Wait (CancellationToken cancellationToken)
 684                 {
 685                         Wait (Timeout.Infinite, cancellationToken);
 686                 }
 687
 688                 public bool Wait (TimeSpan timeout)
 689                 {
 690                         return Wait (CheckTimeout (timeout), CancellationToken.None);
 691                 }
 692
 693                 public bool Wait (int millisecondsTimeout)
 694                 {
 695                         return Wait (millisecondsTimeout, CancellationToken.None);
 696                 }
 697
 698                 public bool Wait (int millisecondsTimeout, CancellationToken cancellationToken)
 699                 {
 700                         if (millisecondsTimeout < -1)
 701                                 throw new ArgumentOutOfRangeException ("millisecondsTimeout");
 702
 703                         bool result = WaitCore (millisecondsTimeout, cancellationToken, true);
 704
 705                         if (IsCanceled)
 706                                 throw new AggregateException (new TaskCanceledException (this));
 707
 708                         var exception = Exception;
 709                         if (exception != null)
 710                                 throw exception;
 711
 712                         return result;
 713                 }
 714
 715                 internal bool WaitCore (int millisecondsTimeout, CancellationToken cancellationToken, bool runInline)
 716                 {
 717                         if (IsCompleted)
 718                                 return true;
 719
 720                         // If the task is ready to be run and we were supposed to wait on it indefinitely without cancellation, just run it
 721                         if (runInline && Status == TaskStatus.WaitingToRun && millisecondsTimeout == Timeout.Infinite && scheduler != null && !cancellationToken.CanBeCanceled) {
 722                                 try {
 723                                         scheduler.RunInline (this, true);
 724                                 } catch (Exception e) {
 725                                         throw new TaskSchedulerException (e);
 726                                 }
 727                         }
 728
 729                         bool result = true;
 730
 731                         if (!IsCompleted) {
 732                                 var continuation = new ManualResetContinuation ();
 733                                 try {
 734                                         ContinueWith (continuation);
 735                                         result = continuation.Event.Wait (millisecondsTimeout, cancellationToken);
 736                                 } finally {
 737                                         if (!result)
 738                                                 RemoveContinuation (continuation);
 739                                         continuation.Dispose ();
 740                                 }
 741                         }
 742
 743                         return result;
 744                 }
 745
 746                 public static void WaitAll (params Task[] tasks)
 747                 {
 748                         WaitAll (tasks, Timeout.Infinite, CancellationToken.None);
 749                 }
 750
 751                 public static void WaitAll (Task[] tasks, CancellationToken cancellationToken)
 752                 {
 753                         WaitAll (tasks, Timeout.Infinite, cancellationToken);
 754                 }
 755
 756                 public static bool WaitAll (Task[] tasks, TimeSpan timeout)
 757                 {
 758                         return WaitAll (tasks, CheckTimeout (timeout), CancellationToken.None);
 759                 }
 760
 761                 public static bool WaitAll (Task[] tasks, int millisecondsTimeout)
 762                 {
 763                         return WaitAll (tasks, millisecondsTimeout, CancellationToken.None);
 764                 }
 765
 766                 public static bool WaitAll (Task[] tasks, int millisecondsTimeout, CancellationToken cancellationToken)
 767                 {
 768                         if (tasks == null)
 769                                 throw new ArgumentNullException ("tasks");
 770
 771                         bool result = true;
 772                         foreach (var t in tasks) {
 773                                 if (t == null)
 774                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
 775
 776                                 result &= t.Status == TaskStatus.RanToCompletion;
 777                         }
 778
 779                         if (!result) {
 780                                 var continuation = new CountdownContinuation (tasks.Length);
 781                                 try {
 782                                         foreach (var t in tasks)
 783                                                 t.ContinueWith (continuation);
 784
 785                                         result = continuation.Event.Wait (millisecondsTimeout, cancellationToken);
 786                                 } finally {
 787                                         List<Exception> exceptions = null;
 788
 789                                         foreach (var t in tasks) {
 790                                                 if (result) {
 791                                                         if (t.Status == TaskStatus.RanToCompletion)
 792                                                                 continue;
 793                                                         if (exceptions == null)
 794                                                                 exceptions = new List<Exception> ();
 795                                                         if (t.Exception != null)
 796                                                                 exceptions.AddRange (t.Exception.InnerExceptions);
 797                                                         else
 798                                                                 exceptions.Add (new TaskCanceledException (t));
 799                                                 } else {
 800                                                         t.RemoveContinuation (continuation);
 801                                                 }
 802                                         }
 803
 804                                         continuation.Dispose ();
 805
 806                                         if (exceptions != null)
 807                                                 throw new AggregateException (exceptions);
 808                                 }
 809                         }
 810
 811                         return result;
 812                 }
 813
 814                 public static int WaitAny (params Task[] tasks)
 815                 {
 816                         return WaitAny (tasks, Timeout.Infinite, CancellationToken.None);
 817                 }
 818
 819                 public static int WaitAny (Task[] tasks, TimeSpan timeout)
 820                 {
 821                         return WaitAny (tasks, CheckTimeout (timeout));
 822                 }
 823
 824                 public static int WaitAny (Task[] tasks, int millisecondsTimeout)
 825                 {
 826                         return WaitAny (tasks, millisecondsTimeout, CancellationToken.None);
 827                 }
 828
 829                 public static int WaitAny (Task[] tasks, CancellationToken cancellationToken)
 830                 {
 831                         return WaitAny (tasks, Timeout.Infinite, cancellationToken);
 832                 }
 833
 834                 public static int WaitAny (Task[] tasks, int millisecondsTimeout, CancellationToken cancellationToken)
 835                 {
 836                         if (tasks == null)
 837                                 throw new ArgumentNullException ("tasks");
 838                         if (millisecondsTimeout < -1)
 839                                 throw new ArgumentOutOfRangeException ("millisecondsTimeout");
 840                         CheckForNullTasks (tasks);
 841
 842                         if (tasks.Length > 0) {
 843                                 var continuation = new ManualResetContinuation ();
 844                                 bool result = false;
 845                                 try {
 846                                         for (int i = 0; i < tasks.Length; i++) {
 847                                                 var t = tasks[i];
 848                                                 if (t.IsCompleted)
 849                                                         return i;
 850                                                 t.ContinueWith (continuation);
 851                                         }
 852
 853                                         if (!(result = continuation.Event.Wait (millisecondsTimeout, cancellationToken)))
 854                                                 return -1;
 855                                 } finally {
 856                                         if (!result)
 857                                                 foreach (var t in tasks)
 858                                                         t.RemoveContinuation (continuation);
 859                                         continuation.Dispose ();
 860                                 }
 861                         }
 862
 863                         int firstFinished = -1;
 864                         for (int i = 0; i < tasks.Length; i++) {
 865                                 var t = tasks[i];
 866                                 if (t.IsCompleted) {
 867                                         firstFinished = i;
 868                                         break;
 869                                 }
 870                         }
 871
 872                         return firstFinished;
 873                 }
 874
 875                 static int CheckTimeout (TimeSpan timeout)
 876                 {
 877                         try {
 878                                 return checked ((int)timeout.TotalMilliseconds);
 879                         } catch (System.OverflowException) {
 880                                 throw new ArgumentOutOfRangeException ("timeout");
 881                         }
 882                 }
 883
 884                 static void CheckForNullTasks (Task[] tasks)
 885                 {
 886                         foreach (var t in tasks)
 887                                 if (t == null)
 888                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
 889                 }
 890                 #endregion
 891
 892                 #region Dispose
 893                 public void Dispose ()
 894                 {
 895                         Dispose (true);
 896                 }
 897
 898                 protected virtual void Dispose (bool disposing)
 899                 {
 900                         if (!IsCompleted)
 901                                 throw new InvalidOperationException ("A task may only be disposed if it is in a completion state");
 902
 903                         // Set action to null so that the GC can collect the delegate and thus
 904                         // any big object references that the user might have captured in a anonymous method
 905                         if (disposing) {
 906                                 parent = null;
 907                                 invoker = null;
 908                                 state = null;
 909                                 if (cancellationRegistration != null)
 910                                         cancellationRegistration.Value.Dispose ();
 911                                 if (wait_handle != null)
 912                                         wait_handle.Dispose ();
 913                         }
 914                 }
 915                 #endregion
 916
 917 #if NET_4_5
 918                 public
 919 #else
 920                 internal
 921 #endif
 922                 Task ContinueWith (Action<Task, object> continuationAction, object state, CancellationToken cancellationToken,
 923                                                                   TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 924                 {
 925                         if (continuationAction == null)
 926                                 throw new ArgumentNullException ("continuationAction");
 927                         if (scheduler == null)
 928                                 throw new ArgumentNullException ("scheduler");
 929
 930                         Task continuation = new Task (TaskActionInvoker.Create (continuationAction),
 931                                                                                   state, cancellationToken,
 932                                                                                   GetCreationOptions (continuationOptions),
 933                                                       parent,
 934                                                       this);
 935                         ContinueWithCore (continuation, continuationOptions, scheduler);
 936
 937                         return continuation;
 938                 }
 939
 940 #if NET_4_5
 941
 942                 public ConfiguredTaskAwaitable ConfigureAwait (bool continueOnCapturedContext)
 943                 {
 944                         return new ConfiguredTaskAwaitable (this, continueOnCapturedContext);
 945                 }
 946
 947                 public Task ContinueWith (Action<Task, object> continuationAction, object state)
 948                 {
 949                         return ContinueWith (continuationAction, state, CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.Current);
 950                 }
 951
 952                 public Task ContinueWith (Action<Task, object> continuationAction, object state, CancellationToken cancellationToken)
 953                 {
 954                         return ContinueWith (continuationAction, state, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 955                 }
 956
 957                 public Task ContinueWith (Action<Task, object> continuationAction, object state, TaskContinuationOptions continuationOptions)
 958                 {
 959                         return ContinueWith (continuationAction, state, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 960                 }
 961
 962                 public Task ContinueWith (Action<Task, object> continuationAction, object state, TaskScheduler scheduler)
 963                 {
 964                         return ContinueWith (continuationAction, state, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 965                 }
 966
 967                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state)
 968                 {
 969                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.Current);
 970                 }
 971
 972                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, TaskContinuationOptions continuationOptions)
 973                 {
 974                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 975                 }
 976
 977                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, CancellationToken cancellationToken)
 978                 {
 979                         return ContinueWith<TResult> (continuationFunction, state, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 980                 }
 981
 982                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, TaskScheduler scheduler)
 983                 {
 984                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 985                 }
 986
 987                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, CancellationToken cancellationToken,
 988                                                                                                         TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 989                 {
 990                         if (continuationFunction == null)
 991                                 throw new ArgumentNullException ("continuationFunction");
 992                         if (scheduler == null)
 993                                 throw new ArgumentNullException ("scheduler");
 994
 995                         var t = new Task<TResult> (TaskActionInvoker.Create (continuationFunction),
 996                                                    state,
 997                                                    cancellationToken,
 998                                                    GetCreationOptions (continuationOptions),
 999                                                    parent,
1000                                                    this);
1001
1002                         ContinueWithCore (t, continuationOptions, scheduler);
1003
1004                         return t;
1005                 }
1006
1007                 public static Task Delay (int millisecondsDelay)
1008                 {
1009                         return Delay (millisecondsDelay, CancellationToken.None);
1010                 }
1011
1012                 public static Task Delay (TimeSpan delay)
1013                 {
1014                         return Delay (CheckTimeout (delay), CancellationToken.None);
1015                 }
1016
1017                 public static Task Delay (TimeSpan delay, CancellationToken cancellationToken)
1018                 {
1019                         return Delay (CheckTimeout (delay), cancellationToken);
1020                 }
1021
1022                 public static Task Delay (int millisecondsDelay, CancellationToken cancellationToken)
1023                 {
1024                         if (millisecondsDelay < -1)
1025                                 throw new ArgumentOutOfRangeException ("millisecondsDelay");
1026
1027                         if (cancellationToken.IsCancellationRequested)
1028                                 return TaskConstants.Canceled;
1029
1030                         var task = new Task (TaskActionInvoker.Empty, null, cancellationToken, TaskCreationOptions.None, null, null);
1031                         task.SetupScheduler (TaskScheduler.Default);
1032
1033                         if (millisecondsDelay != Timeout.Infinite) {
1034                                 var timer = new Timer (delegate (object state) {
1035                                         var t = (Task) state;
1036                                         if (t.Status == TaskStatus.WaitingForActivation) {
1037                                                 t.Status = TaskStatus.Running;
1038                                                 t.Finish ();
1039                                         }
1040                                 }, task, millisecondsDelay, -1);
1041
1042                                 task.ContinueWith (new DisposeContinuation (timer));
1043                         }
1044
1045                         return task;
1046                 }
1047
1048                 public static Task<TResult> FromResult<TResult> (TResult result)
1049                 {
1050                         var tcs = new TaskCompletionSource<TResult> ();
1051                         tcs.SetResult (result);
1052                         return tcs.Task;
1053                 }
1054
1055                 public TaskAwaiter GetAwaiter ()
1056                 {
1057                         return new TaskAwaiter (this);
1058                 }
1059
1060                 public static Task Run (Action action)
1061                 {
1062                         return Run (action, CancellationToken.None);
1063                 }
1064
1065                 public static Task Run (Action action, CancellationToken cancellationToken)
1066                 {
1067                         if (cancellationToken.IsCancellationRequested)
1068                                 return TaskConstants.Canceled;
1069
1070                         return Task.Factory.StartNew (action, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
1071                 }
1072
1073                 public static Task Run (Func<Task> function)
1074                 {
1075                         return Run (function, CancellationToken.None);
1076                 }
1077
1078                 public static Task Run (Func<Task> function, CancellationToken cancellationToken)
1079                 {
1080                         if (cancellationToken.IsCancellationRequested)
1081                                 return TaskConstants.Canceled;
1082
1083                         return TaskExtensionsImpl.Unwrap (Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default));
1084                 }
1085
1086                 public static Task<TResult> Run<TResult> (Func<TResult> function)
1087                 {
1088                         return Run (function, CancellationToken.None);
1089                 }
1090
1091                 public static Task<TResult> Run<TResult> (Func<TResult> function, CancellationToken cancellationToken)
1092                 {
1093                         if (cancellationToken.IsCancellationRequested)
1094                                 return TaskConstants<TResult>.Canceled;
1095
1096                         return Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
1097                 }
1098
1099                 public static Task<TResult> Run<TResult> (Func<Task<TResult>> function)
1100                 {
1101                         return Run (function, CancellationToken.None);
1102                 }
1103
1104                 public static Task<TResult> Run<TResult> (Func<Task<TResult>> function, CancellationToken cancellationToken)
1105                 {
1106                         if (cancellationToken.IsCancellationRequested)
1107                                 return TaskConstants<TResult>.Canceled;
1108
1109                         return TaskExtensionsImpl.Unwrap (Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default));
1110                 }
1111
1112                 public static Task WhenAll (params Task[] tasks)
1113                 {
1114                         if (tasks == null)
1115                                 throw new ArgumentNullException ("tasks");
1116
1117                         return WhenAllCore (tasks);
1118                 }
1119
1120                 public static Task WhenAll (IEnumerable<Task> tasks)
1121                 {
1122                         if (tasks == null)
1123                                 throw new ArgumentNullException ("tasks");
1124
1125                         // Call ToList on input enumeration or we end up
1126                         // enumerating it more than once
1127                         return WhenAllCore (new List<Task> (tasks));
1128                 }
1129
1130                 public static Task<TResult[]> WhenAll<TResult> (params Task<TResult>[] tasks)
1131                 {
1132                         if (tasks == null)
1133                                 throw new ArgumentNullException ("tasks");
1134
1135                         return WhenAllCore<TResult> (tasks);
1136                 }
1137
1138                 public static Task<TResult[]> WhenAll<TResult> (IEnumerable<Task<TResult>> tasks)
1139                 {
1140                         if (tasks == null)
1141                                 throw new ArgumentNullException ("tasks");
1142
1143                         // Call ToList on input enumeration or we end up
1144                         // enumerating it more than once
1145                         return WhenAllCore<TResult> (new List<Task<TResult>> (tasks));
1146                 }
1147
1148                 internal static Task<TResult[]> WhenAllCore<TResult> (IList<Task<TResult>> tasks)
1149                 {
1150                         if (tasks.Count == 0)
1151                                 return FromResult(new TResult[0]);
1152
1153                         foreach (var t in tasks) {
1154                                 if (t == null)
1155                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1156                         }
1157
1158                         var task = new Task<TResult[]> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1159                         task.SetupScheduler (TaskScheduler.Current);
1160
1161                         var continuation = new WhenAllContinuation<TResult> (task, tasks);
1162                         foreach (var t in tasks)
1163                                 t.ContinueWith (continuation);
1164
1165                         return task;
1166                 }
1167
1168                 public static Task<Task> WhenAny (params Task[] tasks)
1169                 {
1170                         if (tasks == null)
1171                                 throw new ArgumentNullException ("tasks");
1172
1173                         return WhenAnyCore (tasks);
1174                 }
1175
1176                 public static Task<Task> WhenAny (IEnumerable<Task> tasks)
1177                 {
1178                         if (tasks == null)
1179                                 throw new ArgumentNullException ("tasks");
1180
1181                         return WhenAnyCore (new List<Task> (tasks));
1182                 }
1183
1184                 public static Task<Task<TResult>> WhenAny<TResult> (params Task<TResult>[] tasks)
1185                 {
1186                         if (tasks == null)
1187                                 throw new ArgumentNullException ("tasks");
1188
1189                         return WhenAnyCore<TResult> (tasks);
1190                 }
1191
1192                 public static Task<Task<TResult>> WhenAny<TResult> (IEnumerable<Task<TResult>> tasks)
1193                 {
1194                         if (tasks == null)
1195                                 throw new ArgumentNullException ("tasks");
1196
1197                         return WhenAnyCore<TResult> (new List<Task<TResult>> (tasks));
1198                 }
1199
1200                 static Task<Task<TResult>> WhenAnyCore<TResult> (IList<Task<TResult>> tasks)
1201                 {
1202                         if (tasks.Count == 0)
1203                                 throw new ArgumentException ("The tasks argument contains no tasks", "tasks");
1204
1205                         int completed_index = -1;
1206                         for (int i = 0; i < tasks.Count; ++i) {
1207                                 var t = tasks[i];
1208                                 if (t == null)
1209                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1210
1211                                 if (t.IsCompleted && completed_index < 0)
1212                                         completed_index = i;
1213                         }
1214
1215                         var task = new Task<Task<TResult>> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1216
1217                         if (completed_index > 0) {
1218                                 task.TrySetResult (tasks[completed_index]);
1219                                 return task;
1220                         }
1221
1222                         task.SetupScheduler (TaskScheduler.Current);
1223
1224                         var continuation = new WhenAnyContinuation<Task<TResult>> (task, tasks);
1225                         foreach (var t in tasks)
1226                                 t.ContinueWith (continuation);
1227
1228                         return task;
1229                 }
1230
1231                 public static YieldAwaitable Yield ()
1232                 {
1233                         return new YieldAwaitable ();
1234                 }
1235 #endif
1236
1237                 internal static Task WhenAllCore (IList<Task> tasks)
1238                 {
1239                         bool all_completed = true;
1240                         foreach (var t in tasks) {
1241                                 if (t == null)
1242                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1243
1244                                 all_completed &= t.Status == TaskStatus.RanToCompletion;
1245                         }
1246
1247                         if (all_completed)
1248                                 return TaskConstants.Finished;
1249
1250                         var task = new Task (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1251                         task.SetupScheduler (TaskScheduler.Current);
1252
1253                         var continuation = new WhenAllContinuation (task, tasks);
1254                         foreach (var t in tasks)
1255                                 t.ContinueWith (continuation);
1256
1257                         return task;
1258                 }
1259
1260                 internal static Task<Task> WhenAnyCore (IList<Task> tasks)
1261                 {
1262                         if (tasks.Count == 0)
1263                                 throw new ArgumentException ("The tasks argument contains no tasks", "tasks");
1264
1265                         int completed_index = -1;
1266                         for (int i = 0; i < tasks.Count; ++i) {
1267                                 var t = tasks [i];
1268                                 if (t == null)
1269                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1270
1271                                 if (t.IsCompleted && completed_index < 0)
1272                                         completed_index = i;
1273                         }
1274
1275                         var task = new Task<Task> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1276
1277                         if (completed_index > 0) {
1278                                 task.TrySetResult (tasks[completed_index]);
1279                                 return task;
1280                         }
1281
1282                         task.SetupScheduler (TaskScheduler.Current);
1283
1284                         var continuation = new WhenAnyContinuation<Task> (task, tasks);
1285                         foreach (var t in tasks)
1286                                 t.ContinueWith (continuation);
1287
1288                         return task;
1289                 }
1290                 #region Properties
1291
1292                 internal CancellationToken CancellationToken {
1293                         get {
1294                                 return token;
1295                         }
1296                 }
1297
1298                 public static TaskFactory Factory {
1299                         get {
1300                                 return defaultFactory;
1301                         }
1302                 }
1303
1304                 public static int? CurrentId {
1305                         get {
1306                                 Task t = current;
1307                                 return t == null ? (int?)null : t.Id;
1308                         }
1309                 }
1310
1311                 public AggregateException Exception {
1312                         get {
1313                                 if (exSlot == null || !IsFaulted)
1314                                         return null;
1315                                 exSlot.Observed = true;
1316                                 return exSlot.Exception;
1317                         }
1318                 }
1319
1320                 public bool IsCanceled {
1321                         get {
1322                                 return status == TaskStatus.Canceled;
1323                         }
1324                 }
1325
1326                 public bool IsCompleted {
1327                         get {
1328                                 return status >= TaskStatus.RanToCompletion;
1329                         }
1330                 }
1331
1332                 public bool IsFaulted {
1333                         get {
1334                                 return status == TaskStatus.Faulted;
1335                         }
1336                 }
1337
1338                 public TaskCreationOptions CreationOptions {
1339                         get {
1340                                 return creationOptions & MaxTaskCreationOptions;
1341                         }
1342                 }
1343
1344                 public TaskStatus Status {
1345                         get {
1346                                 return status;
1347                         }
1348                         internal set {
1349                                 status = value;
1350                                 Thread.MemoryBarrier ();
1351                         }
1352                 }
1353
1354                 internal TaskExceptionSlot ExceptionSlot {
1355                         get {
1356                                 if (exSlot != null)
1357                                         return exSlot;
1358                                 Interlocked.CompareExchange (ref exSlot, new TaskExceptionSlot (this), null);
1359                                 return exSlot;
1360                         }
1361                 }
1362
1363                 public object AsyncState {
1364                         get {
1365                                 return state;
1366                         }
1367                 }
1368
1369                 bool IAsyncResult.CompletedSynchronously {
1370                         get {
1371                                 return false;
1372                         }
1373                 }
1374
1375                 WaitHandle IAsyncResult.AsyncWaitHandle {
1376                         get {
1377                                 if (invoker == null)
1378                                         throw new ObjectDisposedException (GetType ().ToString ());
1379
1380                                 if (wait_handle == null)
1381                                         Interlocked.CompareExchange (ref wait_handle, new ManualResetEvent (IsCompleted), null);
1382
1383                                 return wait_handle;
1384                         }
1385                 }
1386
1387                 public int Id {
1388                         get {
1389                                 return taskId;
1390                         }
1391                 }
1392
1393                 bool IsContinuation {
1394                         get {
1395                                 return contAncestor != null;
1396                         }
1397                 }
1398
1399                 bool IsPromise {
1400                         get {
1401                                 return invoker == TaskActionInvoker.Promise;
1402                         }
1403                 }
1404
1405                 internal Task ContinuationAncestor {
1406                         get {
1407                                 return contAncestor;
1408                         }
1409                 }
1410
1411                 internal string DisplayActionMethod {
1412                         get {
1413                                 Delegate d = invoker.Action;
1414                                 return d == null ? "<none>" : d.Method.ToString ();
1415                         }
1416                 }
1417
1418                 #endregion
1419         }
1420 }
1421 #endif