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 = true;
 645
 646                         if (!IsCompleted) {
 647                                 // If the task is ready to be run and we were supposed to wait on it indefinitely without cancellation, just run it
 648                                 if (Status == TaskStatus.WaitingToRun && millisecondsTimeout == Timeout.Infinite && scheduler != null && !cancellationToken.CanBeCanceled)
 649                                         scheduler.RunInline (this, true);
 650
 651                                 if (!IsCompleted) {
 652                                         var continuation = new ManualResetContinuation ();
 653                                         try {
 654                                                 ContinueWith (continuation);
 655                                                 result = continuation.Event.Wait (millisecondsTimeout, cancellationToken);
 656                                         } finally {
 657                                                 if (!result)
 658                                                         RemoveContinuation (continuation);
 659                                                 continuation.Dispose ();
 660                                         }
 661                                 }
 662                         }
 663
 664                         if (IsCanceled)
 665                                 throw new AggregateException (new TaskCanceledException (this));
 666
 667                         var exception = Exception;
 668                         if (exception != null)
 669                                 throw exception;
 670
 671                         return result;
 672                 }
 673
 674                 public static void WaitAll (params Task[] tasks)
 675                 {
 676                         WaitAll (tasks, Timeout.Infinite, CancellationToken.None);
 677                 }
 678
 679                 public static void WaitAll (Task[] tasks, CancellationToken cancellationToken)
 680                 {
 681                         WaitAll (tasks, Timeout.Infinite, cancellationToken);
 682                 }
 683
 684                 public static bool WaitAll (Task[] tasks, TimeSpan timeout)
 685                 {
 686                         return WaitAll (tasks, CheckTimeout (timeout), CancellationToken.None);
 687                 }
 688
 689                 public static bool WaitAll (Task[] tasks, int millisecondsTimeout)
 690                 {
 691                         return WaitAll (tasks, millisecondsTimeout, CancellationToken.None);
 692                 }
 693
 694                 public static bool WaitAll (Task[] tasks, int millisecondsTimeout, CancellationToken cancellationToken)
 695                 {
 696                         if (tasks == null)
 697                                 throw new ArgumentNullException ("tasks");
 698
 699                         bool result = true;
 700                         foreach (var t in tasks) {
 701                                 if (t == null)
 702                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
 703
 704                                 result &= t.Status == TaskStatus.RanToCompletion;
 705                         }
 706
 707                         if (!result) {
 708                                 var continuation = new CountdownContinuation (tasks.Length);
 709                                 try {
 710                                         foreach (var t in tasks)
 711                                                 t.ContinueWith (continuation);
 712
 713                                         result = continuation.Event.Wait (millisecondsTimeout, cancellationToken);
 714                                 } finally {
 715                                         List<Exception> exceptions = null;
 716
 717                                         foreach (var t in tasks) {
 718                                                 if (result) {
 719                                                         if (t.Status == TaskStatus.RanToCompletion)
 720                                                                 continue;
 721                                                         if (exceptions == null)
 722                                                                 exceptions = new List<Exception> ();
 723                                                         if (t.Exception != null)
 724                                                                 exceptions.AddRange (t.Exception.InnerExceptions);
 725                                                         else
 726                                                                 exceptions.Add (new TaskCanceledException (t));
 727                                                 } else {
 728                                                         t.RemoveContinuation (continuation);
 729                                                 }
 730                                         }
 731
 732                                         continuation.Dispose ();
 733
 734                                         if (exceptions != null)
 735                                                 throw new AggregateException (exceptions);
 736                                 }
 737                         }
 738
 739                         return result;
 740                 }
 741
 742                 public static int WaitAny (params Task[] tasks)
 743                 {
 744                         return WaitAny (tasks, Timeout.Infinite, CancellationToken.None);
 745                 }
 746
 747                 public static int WaitAny (Task[] tasks, TimeSpan timeout)
 748                 {
 749                         return WaitAny (tasks, CheckTimeout (timeout));
 750                 }
 751
 752                 public static int WaitAny (Task[] tasks, int millisecondsTimeout)
 753                 {
 754                         return WaitAny (tasks, millisecondsTimeout, CancellationToken.None);
 755                 }
 756
 757                 public static int WaitAny (Task[] tasks, CancellationToken cancellationToken)
 758                 {
 759                         return WaitAny (tasks, Timeout.Infinite, cancellationToken);
 760                 }
 761
 762                 public static int WaitAny (Task[] tasks, int millisecondsTimeout, CancellationToken cancellationToken)
 763                 {
 764                         if (tasks == null)
 765                                 throw new ArgumentNullException ("tasks");
 766                         if (millisecondsTimeout < -1)
 767                                 throw new ArgumentOutOfRangeException ("millisecondsTimeout");
 768                         CheckForNullTasks (tasks);
 769
 770                         if (tasks.Length > 0) {
 771                                 var continuation = new ManualResetContinuation ();
 772                                 bool result = false;
 773                                 try {
 774                                         for (int i = 0; i < tasks.Length; i++) {
 775                                                 var t = tasks[i];
 776                                                 if (t.IsCompleted)
 777                                                         return i;
 778                                                 t.ContinueWith (continuation);
 779                                         }
 780
 781                                         if (!(result = continuation.Event.Wait (millisecondsTimeout, cancellationToken)))
 782                                                 return -1;
 783                                 } finally {
 784                                         if (!result)
 785                                                 foreach (var t in tasks)
 786                                                         t.RemoveContinuation (continuation);
 787                                         continuation.Dispose ();
 788                                 }
 789                         }
 790
 791                         int firstFinished = -1;
 792                         for (int i = 0; i < tasks.Length; i++) {
 793                                 var t = tasks[i];
 794                                 if (t.IsCompleted) {
 795                                         firstFinished = i;
 796                                         break;
 797                                 }
 798                         }
 799
 800                         return firstFinished;
 801                 }
 802
 803                 static int CheckTimeout (TimeSpan timeout)
 804                 {
 805                         try {
 806                                 return checked ((int)timeout.TotalMilliseconds);
 807                         } catch (System.OverflowException) {
 808                                 throw new ArgumentOutOfRangeException ("timeout");
 809                         }
 810                 }
 811
 812                 static void CheckForNullTasks (Task[] tasks)
 813                 {
 814                         foreach (var t in tasks)
 815                                 if (t == null)
 816                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
 817                 }
 818                 #endregion
 819
 820                 #region Dispose
 821                 public void Dispose ()
 822                 {
 823                         Dispose (true);
 824                 }
 825
 826                 protected virtual void Dispose (bool disposing)
 827                 {
 828                         if (!IsCompleted)
 829                                 throw new InvalidOperationException ("A task may only be disposed if it is in a completion state");
 830
 831                         // Set action to null so that the GC can collect the delegate and thus
 832                         // any big object references that the user might have captured in a anonymous method
 833                         if (disposing) {
 834                                 invoker = null;
 835                                 state = null;
 836                                 if (cancellationRegistration != null)
 837                                         cancellationRegistration.Value.Dispose ();
 838                                 if (wait_handle != null)
 839                                         wait_handle.Dispose ();
 840                         }
 841                 }
 842                 #endregion
 843
 844 #if NET_4_5
 845                 public
 846 #else
 847                 internal
 848 #endif
 849                 Task ContinueWith (Action<Task, object> continuationAction, object state, CancellationToken cancellationToken,
 850                                                                   TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 851                 {
 852                         if (continuationAction == null)
 853                                 throw new ArgumentNullException ("continuationAction");
 854                         if (scheduler == null)
 855                                 throw new ArgumentNullException ("scheduler");
 856
 857                         Task continuation = new Task (TaskActionInvoker.Create (continuationAction),
 858                                                                                   state, cancellationToken,
 859                                                                                   GetCreationOptions (continuationOptions),
 860                                                       parent,
 861                                                       this);
 862                         ContinueWithCore (continuation, continuationOptions, scheduler);
 863
 864                         return continuation;
 865                 }
 866
 867 #if NET_4_5
 868
 869                 public ConfiguredTaskAwaitable ConfigureAwait (bool continueOnCapturedContext)
 870                 {
 871                         return new ConfiguredTaskAwaitable (this, continueOnCapturedContext);
 872                 }
 873
 874                 public Task ContinueWith (Action<Task, object> continuationAction, object state)
 875                 {
 876                         return ContinueWith (continuationAction, state, CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.Current);
 877                 }
 878
 879                 public Task ContinueWith (Action<Task, object> continuationAction, object state, CancellationToken cancellationToken)
 880                 {
 881                         return ContinueWith (continuationAction, state, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 882                 }
 883
 884                 public Task ContinueWith (Action<Task, object> continuationAction, object state, TaskContinuationOptions continuationOptions)
 885                 {
 886                         return ContinueWith (continuationAction, state, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 887                 }
 888
 889                 public Task ContinueWith (Action<Task, object> continuationAction, object state, TaskScheduler scheduler)
 890                 {
 891                         return ContinueWith (continuationAction, state, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 892                 }
 893
 894                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state)
 895                 {
 896                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, TaskContinuationOptions.None, TaskScheduler.Current);
 897                 }
 898
 899                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, TaskContinuationOptions continuationOptions)
 900                 {
 901                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, continuationOptions, TaskScheduler.Current);
 902                 }
 903
 904                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, CancellationToken cancellationToken)
 905                 {
 906                         return ContinueWith<TResult> (continuationFunction, state, cancellationToken, TaskContinuationOptions.None, TaskScheduler.Current);
 907                 }
 908
 909                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, TaskScheduler scheduler)
 910                 {
 911                         return ContinueWith<TResult> (continuationFunction, state, CancellationToken.None, TaskContinuationOptions.None, scheduler);
 912                 }
 913
 914                 public Task<TResult> ContinueWith<TResult> (Func<Task, object, TResult> continuationFunction, object state, CancellationToken cancellationToken,
 915                                                                                                         TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
 916                 {
 917                         if (continuationFunction == null)
 918                                 throw new ArgumentNullException ("continuationFunction");
 919                         if (scheduler == null)
 920                                 throw new ArgumentNullException ("scheduler");
 921
 922                         var t = new Task<TResult> (TaskActionInvoker.Create (continuationFunction),
 923                                                    state,
 924                                                    cancellationToken,
 925                                                    GetCreationOptions (continuationOptions),
 926                                                    parent,
 927                                                    this);
 928
 929                         ContinueWithCore (t, continuationOptions, scheduler);
 930
 931                         return t;
 932                 }
 933
 934                 public static Task Delay (int millisecondsDelay)
 935                 {
 936                         return Delay (millisecondsDelay, CancellationToken.None);
 937                 }
 938
 939                 public static Task Delay (TimeSpan delay)
 940                 {
 941                         return Delay (CheckTimeout (delay), CancellationToken.None);
 942                 }
 943
 944                 public static Task Delay (TimeSpan delay, CancellationToken cancellationToken)
 945                 {
 946                         return Delay (CheckTimeout (delay), cancellationToken);
 947                 }
 948
 949                 public static Task Delay (int millisecondsDelay, CancellationToken cancellationToken)
 950                 {
 951                         if (millisecondsDelay < -1)
 952                                 throw new ArgumentOutOfRangeException ("millisecondsDelay");
 953
 954                         var task = new Task (TaskActionInvoker.Delay, millisecondsDelay, cancellationToken, TaskCreationOptions.None, null, TaskConstants.Finished);
 955                         task.SetupScheduler (TaskScheduler.Current);
 956
 957                         if (millisecondsDelay != Timeout.Infinite)
 958                                 task.scheduler.QueueTask (task);
 959
 960                         return task;
 961                 }
 962
 963                 public static Task<TResult> FromResult<TResult> (TResult result)
 964                 {
 965                         var tcs = new TaskCompletionSource<TResult> ();
 966                         tcs.SetResult (result);
 967                         return tcs.Task;
 968                 }
 969
 970                 public TaskAwaiter GetAwaiter ()
 971                 {
 972                         return new TaskAwaiter (this);
 973                 }
 974
 975                 public static Task Run (Action action)
 976                 {
 977                         return Run (action, CancellationToken.None);
 978                 }
 979
 980                 public static Task Run (Action action, CancellationToken cancellationToken)
 981                 {
 982                         if (cancellationToken.IsCancellationRequested)
 983                                 return TaskConstants.Canceled;
 984
 985                         return Task.Factory.StartNew (action, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
 986                 }
 987
 988                 public static Task Run (Func<Task> function)
 989                 {
 990                         return Run (function, CancellationToken.None);
 991                 }
 992
 993                 public static Task Run (Func<Task> function, CancellationToken cancellationToken)
 994                 {
 995                         if (cancellationToken.IsCancellationRequested)
 996                                 return TaskConstants.Canceled;
 997
 998                         return TaskExtensionsImpl.Unwrap (Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default));
 999                 }
1000
1001                 public static Task<TResult> Run<TResult> (Func<TResult> function)
1002                 {
1003                         return Run (function, CancellationToken.None);
1004                 }
1005
1006                 public static Task<TResult> Run<TResult> (Func<TResult> function, CancellationToken cancellationToken)
1007                 {
1008                         if (cancellationToken.IsCancellationRequested)
1009                                 return TaskConstants<TResult>.Canceled;
1010
1011                         return Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
1012                 }
1013
1014                 public static Task<TResult> Run<TResult> (Func<Task<TResult>> function)
1015                 {
1016                         return Run (function, CancellationToken.None);
1017                 }
1018
1019                 public static Task<TResult> Run<TResult> (Func<Task<TResult>> function, CancellationToken cancellationToken)
1020                 {
1021                         if (cancellationToken.IsCancellationRequested)
1022                                 return TaskConstants<TResult>.Canceled;
1023
1024                         return TaskExtensionsImpl.Unwrap (Task.Factory.StartNew (function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default));
1025                 }
1026
1027                 public static Task WhenAll (params Task[] tasks)
1028                 {
1029                         if (tasks == null)
1030                                 throw new ArgumentNullException ("tasks");
1031
1032                         return WhenAllCore (tasks);
1033                 }
1034
1035                 public static Task WhenAll (IEnumerable<Task> tasks)
1036                 {
1037                         if (tasks == null)
1038                                 throw new ArgumentNullException ("tasks");
1039
1040                         // Call ToList on input enumeration or we end up
1041                         // enumerating it more than once
1042                         return WhenAllCore (new List<Task> (tasks));
1043                 }
1044
1045                 public static Task<TResult[]> WhenAll<TResult> (params Task<TResult>[] tasks)
1046                 {
1047                         if (tasks == null)
1048                                 throw new ArgumentNullException ("tasks");
1049
1050                         return WhenAllCore<TResult> (tasks);
1051                 }
1052
1053                 public static Task<TResult[]> WhenAll<TResult> (IEnumerable<Task<TResult>> tasks)
1054                 {
1055                         if (tasks == null)
1056                                 throw new ArgumentNullException ("tasks");
1057
1058                         // Call ToList on input enumeration or we end up
1059                         // enumerating it more than once
1060                         return WhenAllCore<TResult> (new List<Task<TResult>> (tasks));
1061                 }
1062
1063                 internal static Task<TResult[]> WhenAllCore<TResult> (IList<Task<TResult>> tasks)
1064                 {
1065                         foreach (var t in tasks) {
1066                                 if (t == null)
1067                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1068                         }
1069
1070                         var task = new Task<TResult[]> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1071                         task.SetupScheduler (TaskScheduler.Current);
1072
1073                         var continuation = new WhenAllContinuation<TResult> (task, tasks);
1074                         foreach (var t in tasks)
1075                                 t.ContinueWith (continuation);
1076
1077                         return task;
1078                 }
1079
1080                 public static Task<Task> WhenAny (params Task[] tasks)
1081                 {
1082                         if (tasks == null)
1083                                 throw new ArgumentNullException ("tasks");
1084
1085                         return WhenAnyCore (tasks);
1086                 }
1087
1088                 public static Task<Task> WhenAny (IEnumerable<Task> tasks)
1089                 {
1090                         if (tasks == null)
1091                                 throw new ArgumentNullException ("tasks");
1092
1093                         return WhenAnyCore (new List<Task> (tasks));
1094                 }
1095
1096                 public static Task<Task<TResult>> WhenAny<TResult> (params Task<TResult>[] tasks)
1097                 {
1098                         if (tasks == null)
1099                                 throw new ArgumentNullException ("tasks");
1100
1101                         return WhenAnyCore<TResult> (tasks);
1102                 }
1103
1104                 public static Task<Task<TResult>> WhenAny<TResult> (IEnumerable<Task<TResult>> tasks)
1105                 {
1106                         if (tasks == null)
1107                                 throw new ArgumentNullException ("tasks");
1108
1109                         return WhenAnyCore<TResult> (new List<Task<TResult>> (tasks));
1110                 }
1111
1112                 static Task<Task<TResult>> WhenAnyCore<TResult> (IList<Task<TResult>> tasks)
1113                 {
1114                         if (tasks.Count == 0)
1115                                 throw new ArgumentException ("The tasks argument contains no tasks", "tasks");
1116
1117                         int completed_index = -1;
1118                         for (int i = 0; i < tasks.Count; ++i) {
1119                                 var t = tasks[i];
1120                                 if (t == null)
1121                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1122
1123                                 if (t.IsCompleted && completed_index < 0)
1124                                         completed_index = i;
1125                         }
1126
1127                         var task = new Task<Task<TResult>> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1128
1129                         if (completed_index > 0) {
1130                                 task.TrySetResult (tasks[completed_index]);
1131                                 return task;
1132                         }
1133
1134                         task.SetupScheduler (TaskScheduler.Current);
1135
1136                         var continuation = new WhenAnyContinuation<Task<TResult>> (task, tasks);
1137                         foreach (var t in tasks)
1138                                 t.ContinueWith (continuation);
1139
1140                         return task;
1141                 }
1142
1143                 public static YieldAwaitable Yield ()
1144                 {
1145                         return new YieldAwaitable ();
1146                 }
1147 #endif
1148
1149                 internal static Task WhenAllCore (IList<Task> tasks)
1150                 {
1151                         bool all_completed = true;
1152                         foreach (var t in tasks) {
1153                                 if (t == null)
1154                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1155
1156                                 all_completed &= t.Status == TaskStatus.RanToCompletion;
1157                         }
1158
1159                         if (all_completed)
1160                                 return TaskConstants.Finished;
1161
1162                         var task = new Task (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1163                         task.SetupScheduler (TaskScheduler.Current);
1164
1165                         var continuation = new WhenAllContinuation (task, tasks);
1166                         foreach (var t in tasks)
1167                                 t.ContinueWith (continuation);
1168
1169                         return task;
1170                 }
1171
1172                 internal static Task<Task> WhenAnyCore (IList<Task> tasks)
1173                 {
1174                         if (tasks.Count == 0)
1175                                 throw new ArgumentException ("The tasks argument contains no tasks", "tasks");
1176
1177                         int completed_index = -1;
1178                         for (int i = 0; i < tasks.Count; ++i) {
1179                                 var t = tasks [i];
1180                                 if (t == null)
1181                                         throw new ArgumentException ("tasks", "the tasks argument contains a null element");
1182
1183                                 if (t.IsCompleted && completed_index < 0)
1184                                         completed_index = i;
1185                         }
1186
1187                         var task = new Task<Task> (TaskActionInvoker.Empty, null, CancellationToken.None, TaskCreationOptions.None, null, TaskConstants.Finished);
1188
1189                         if (completed_index > 0) {
1190                                 task.TrySetResult (tasks[completed_index]);
1191                                 return task;
1192                         }
1193
1194                         task.SetupScheduler (TaskScheduler.Current);
1195
1196                         var continuation = new WhenAnyContinuation<Task> (task, tasks);
1197                         foreach (var t in tasks)
1198                                 t.ContinueWith (continuation);
1199
1200                         return task;
1201                 }
1202                 #region Properties
1203
1204                 internal CancellationToken CancellationToken {
1205                         get {
1206                                 return token;
1207                         }
1208                 }
1209
1210                 public static TaskFactory Factory {
1211                         get {
1212                                 return defaultFactory;
1213                         }
1214                 }
1215
1216                 public static int? CurrentId {
1217                         get {
1218                                 Task t = current;
1219                                 return t == null ? (int?)null : t.Id;
1220                         }
1221                 }
1222
1223                 public AggregateException Exception {
1224                         get {
1225                                 if (exSlot == null)
1226                                         return null;
1227                                 exSlot.Observed = true;
1228                                 return exSlot.Exception;
1229                         }
1230                 }
1231
1232                 public bool IsCanceled {
1233                         get {
1234                                 return status == TaskStatus.Canceled;
1235                         }
1236                 }
1237
1238                 public bool IsCompleted {
1239                         get {
1240                                 return status >= TaskStatus.RanToCompletion;
1241                         }
1242                 }
1243
1244                 public bool IsFaulted {
1245                         get {
1246                                 return status == TaskStatus.Faulted;
1247                         }
1248                 }
1249
1250                 public TaskCreationOptions CreationOptions {
1251                         get {
1252                                 return creationOptions & MaxTaskCreationOptions;
1253                         }
1254                 }
1255
1256                 public TaskStatus Status {
1257                         get {
1258                                 return status;
1259                         }
1260                         internal set {
1261                                 status = value;
1262                                 Thread.MemoryBarrier ();
1263                         }
1264                 }
1265
1266                 TaskExceptionSlot ExceptionSlot {
1267                         get {
1268                                 if (exSlot != null)
1269                                         return exSlot;
1270                                 Interlocked.CompareExchange (ref exSlot, new TaskExceptionSlot (this), null);
1271                                 return exSlot;
1272                         }
1273                 }
1274
1275                 public object AsyncState {
1276                         get {
1277                                 return state;
1278                         }
1279                 }
1280
1281                 bool IAsyncResult.CompletedSynchronously {
1282                         get {
1283                                 return true;
1284                         }
1285                 }
1286
1287                 WaitHandle IAsyncResult.AsyncWaitHandle {
1288                         get {
1289                                 if (invoker == null)
1290                                         throw new ObjectDisposedException (GetType ().ToString ());
1291
1292                                 if (wait_handle == null)
1293                                         Interlocked.CompareExchange (ref wait_handle, new ManualResetEvent (IsCompleted), null);
1294
1295                                 return wait_handle;
1296                         }
1297                 }
1298
1299                 public int Id {
1300                         get {
1301                                 return taskId;
1302                         }
1303                 }
1304
1305                 bool IsContinuation {
1306                         get {
1307                                 return contAncestor != null;
1308                         }
1309                 }
1310
1311                 internal Task ContinuationAncestor {
1312                         get {
1313                                 return contAncestor;
1314                         }
1315                 }
1316
1317                 internal string DisplayActionMethod {
1318                         get {
1319                                 Delegate d = invoker.Action;
1320                                 return d == null ? "<none>" : d.Method.ToString ();
1321                         }
1322                 }
1323
1324                 #endregion
1325         }
1326 }
1327 #endif