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