mcs/mcs/async.cs

   1 //
   2 // async.cs: Asynchronous functions
   3 //
   4 // Author:
   5 //   Marek Safar (marek.safar@gmail.com)
   6 //
   7 // Dual licensed under the terms of the MIT X11 or GNU GPL
   8 //
   9 // Copyright 2011 Novell, Inc.
  10 // Copyright 2011-2012 Xamarin Inc.
  11 //
  12
  13 using System;
  14 using System.Collections.Generic;
  15 using System.Linq;
  16 using System.Collections;
  17
  18 #if STATIC
  19 using IKVM.Reflection;
  20 using IKVM.Reflection.Emit;
  21 #else
  22 using System.Reflection;
  23 using System.Reflection.Emit;
  24 #endif
  25
  26 namespace Mono.CSharp
  27 {
  28         public class Await : ExpressionStatement
  29         {
  30                 Expression expr;
  31                 AwaitStatement stmt;
  32
  33                 public Await (Expression expr, Location loc)
  34                 {
  35                         this.expr = expr;
  36                         this.loc = loc;
  37                 }
  38
  39                 public Expression Expr {
  40                         get {
  41                                 return expr;
  42                         }
  43                 }
  44
  45                 public AwaitStatement Statement {
  46                         get {
  47                                 return stmt;
  48                         }
  49                 }
  50
  51                 protected override void CloneTo (CloneContext clonectx, Expression target)
  52                 {
  53                         var t = (Await) target;
  54
  55                         t.expr = expr.Clone (clonectx);
  56                 }
  57
  58                 public override Expression CreateExpressionTree (ResolveContext ec)
  59                 {
  60                         throw new NotImplementedException ("ET");
  61                 }
  62
  63                 public override bool ContainsEmitWithAwait ()
  64                 {
  65                         return true;
  66                 }
  67
  68                 protected override Expression DoResolve (ResolveContext rc)
  69                 {
  70                         if (rc.HasSet (ResolveContext.Options.LockScope)) {
  71                                 rc.Report.Error (1996, loc,
  72                                         "The `await' operator cannot be used in the body of a lock statement");
  73                         }
  74
  75                         if (rc.IsUnsafe) {
  76                                 rc.Report.Error (4004, loc,
  77                                         "The `await' operator cannot be used in an unsafe context");
  78                         }
  79
  80                         var bc = (BlockContext) rc;
  81
  82                         stmt = new AwaitStatement (expr, loc);
  83                         if (!stmt.Resolve (bc))
  84                                 return null;
  85
  86                         type = stmt.ResultType;
  87                         eclass = ExprClass.Variable;
  88                         return this;
  89                 }
  90
  91                 public override void Emit (EmitContext ec)
  92                 {
  93                         stmt.EmitPrologue (ec);
  94
  95                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
  96                                 stmt.Emit (ec);
  97                         }
  98                 }
  99
 100                 public override Expression EmitToField (EmitContext ec)
 101                 {
 102                         stmt.EmitPrologue (ec);
 103                         return stmt.GetResultExpression (ec);
 104                 }
 105
 106                 public void EmitAssign (EmitContext ec, FieldExpr field)
 107                 {
 108                         stmt.EmitPrologue (ec);
 109                         field.InstanceExpression.Emit (ec);
 110                         stmt.Emit (ec);
 111                 }
 112
 113                 public override void EmitStatement (EmitContext ec)
 114                 {
 115                         stmt.EmitStatement (ec);
 116                 }
 117
 118                 public override object Accept (StructuralVisitor visitor)
 119                 {
 120                         return visitor.Visit (this);
 121                 }
 122         }
 123
 124         public class AwaitStatement : YieldStatement<AsyncInitializer>
 125         {
 126                 public sealed class AwaitableMemberAccess : MemberAccess
 127                 {
 128                         public AwaitableMemberAccess (Expression expr)
 129                                 : base (expr, "GetAwaiter")
 130                         {
 131                         }
 132
 133                         public bool ProbingMode { get; set; }
 134
 135                         protected override void Error_TypeDoesNotContainDefinition (ResolveContext rc, TypeSpec type, string name)
 136                         {
 137                                 Error_OperatorCannotBeApplied (rc, type);
 138                         }
 139
 140                         protected override void Error_OperatorCannotBeApplied (ResolveContext rc, TypeSpec type)
 141                         {
 142                                 if (ProbingMode)
 143                                         return;
 144
 145                                 var invocation = LeftExpression as Invocation;
 146                                 if (invocation != null && invocation.MethodGroup != null && (invocation.MethodGroup.BestCandidate.Modifiers & Modifiers.ASYNC) != 0) {
 147                                         rc.Report.Error (4008, loc, "Cannot await void method `{0}'. Consider changing method return type to `Task'",
 148                                                 invocation.GetSignatureForError ());
 149                                 } else {
 150                                         rc.Report.Error (4001, loc, "Cannot await `{0}' expression", type.GetSignatureForError ());
 151                                 }
 152                         }
 153                 }
 154
 155                 sealed class GetResultInvocation : Invocation
 156                 {
 157                         public GetResultInvocation (MethodGroupExpr mge, Arguments arguments)
 158                                 : base (null, arguments)
 159                         {
 160                                 mg = mge;
 161                                 type = mg.BestCandidateReturnType;
 162                         }
 163
 164                         public override Expression EmitToField (EmitContext ec)
 165                         {
 166                                 return this;
 167                         }
 168                 }
 169
 170                 Field awaiter;
 171                 AwaiterDefinition awaiter_definition;
 172                 TypeSpec type;
 173                 TypeSpec result_type;
 174
 175                 public AwaitStatement (Expression expr, Location loc)
 176                         : base (expr, loc)
 177                 {
 178                 }
 179
 180                 #region Properties
 181
 182                 bool IsDynamic {
 183                         get {
 184                                 return awaiter_definition == null;
 185                         }
 186                 }
 187
 188                 public TypeSpec ResultType {
 189                         get {
 190                                 return result_type;
 191                         }
 192                 }
 193
 194                 #endregion
 195
 196                 protected override void DoEmit (EmitContext ec)
 197                 {
 198                         GetResultExpression (ec).Emit (ec);
 199                 }
 200
 201                 public Expression GetResultExpression (EmitContext ec)
 202                 {
 203                         var fe_awaiter = new FieldExpr (awaiter, loc);
 204                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 205
 206                         //
 207                         // result = awaiter.GetResult ();
 208                         //
 209                         if (IsDynamic) {
 210                                 var rc = new ResolveContext (ec.MemberContext);
 211                                 return new Invocation (new MemberAccess (fe_awaiter, "GetResult"), new Arguments (0)).Resolve (rc);
 212                         }
 213
 214                         var mg_result = MethodGroupExpr.CreatePredefined (awaiter_definition.GetResult, fe_awaiter.Type, loc);
 215                         mg_result.InstanceExpression = fe_awaiter;
 216
 217                         return new GetResultInvocation (mg_result, new Arguments (0));
 218                 }
 219
 220                 public void EmitPrologue (EmitContext ec)
 221                 {
 222                         awaiter = ((AsyncTaskStorey) machine_initializer.Storey).AddAwaiter (expr.Type, loc);
 223
 224                         var fe_awaiter = new FieldExpr (awaiter, loc);
 225                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 226
 227                         //
 228                         // awaiter = expr.GetAwaiter ();
 229                         //
 230                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 231                                 fe_awaiter.EmitAssign (ec, expr, false, false);
 232                         }
 233
 234                         Label skip_continuation = ec.DefineLabel ();
 235
 236                         Expression completed_expr;
 237                         if (IsDynamic) {
 238                                 var rc = new ResolveContext (ec.MemberContext);
 239
 240                                 Arguments dargs = new Arguments (1);
 241                                 dargs.Add (new Argument (fe_awaiter));
 242                                 completed_expr = new DynamicMemberBinder ("IsCompleted", dargs, loc).Resolve (rc);
 243
 244                                 dargs = new Arguments (1);
 245                                 dargs.Add (new Argument (completed_expr));
 246                                 completed_expr = new DynamicConversion (ec.Module.Compiler.BuiltinTypes.Bool, 0, dargs, loc).Resolve (rc);
 247                         } else {
 248                                 var pe = PropertyExpr.CreatePredefined (awaiter_definition.IsCompleted, loc);
 249                                 pe.InstanceExpression = fe_awaiter;
 250                                 completed_expr = pe;
 251                         }
 252
 253                         completed_expr.EmitBranchable (ec, skip_continuation, true);
 254
 255                         base.DoEmit (ec);
 256
 257                         //
 258                         // The stack has to be empty before calling await continuation. We handle this
 259                         // by lifting values which would be left on stack into class fields. The process
 260                         // is quite complicated and quite hard to test because any expression can possibly
 261                         // leave a value on the stack.
 262                         //
 263                         // Following assert fails when some of expression called before is missing EmitToField
 264                         // or parent expression fails to find await in children expressions
 265                         //
 266                         ec.AssertEmptyStack ();
 267
 268                         var storey = (AsyncTaskStorey) machine_initializer.Storey;
 269                         if (IsDynamic) {
 270                                 storey.EmitAwaitOnCompletedDynamic (ec, fe_awaiter);
 271                         } else {
 272                                 storey.EmitAwaitOnCompleted (ec, fe_awaiter);
 273                         }
 274
 275                         // Return ok
 276                         machine_initializer.EmitLeave (ec, unwind_protect);
 277
 278                         ec.MarkLabel (resume_point);
 279                         ec.MarkLabel (skip_continuation);
 280                 }
 281
 282                 public void EmitStatement (EmitContext ec)
 283                 {
 284                         EmitPrologue (ec);
 285                         DoEmit (ec);
 286
 287                         awaiter.IsAvailableForReuse = true;
 288
 289                         if (ResultType.Kind != MemberKind.Void)
 290                                 ec.Emit (OpCodes.Pop);
 291                 }
 292
 293                 void Error_WrongAwaiterPattern (ResolveContext rc, TypeSpec awaiter)
 294                 {
 295                         rc.Report.Error (4011, loc, "The awaiter type `{0}' must have suitable IsCompleted and GetResult members",
 296                                 awaiter.GetSignatureForError ());
 297                 }
 298
 299                 public override bool Resolve (BlockContext bc)
 300                 {
 301                         if (bc.CurrentBlock is Linq.QueryBlock) {
 302                                 bc.Report.Error (1995, loc,
 303                                         "The `await' operator may only be used in a query expression within the first collection expression of the initial `from' clause or within the collection expression of a `join' clause");
 304                                 return false;
 305                         }
 306
 307                         if (!base.Resolve (bc))
 308                                 return false;
 309
 310                         type = expr.Type;
 311                         Arguments args = new Arguments (0);
 312
 313                         //
 314                         // The await expression is of dynamic type
 315                         //
 316                         if (type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 317                                 result_type = type;
 318                                 expr = new Invocation (new MemberAccess (expr, "GetAwaiter"), args).Resolve (bc);
 319                                 return true;
 320                         }
 321
 322                         //
 323                         // Check whether the expression is awaitable
 324                         //
 325                         Expression ama = new AwaitableMemberAccess (expr).Resolve (bc);
 326                         if (ama == null)
 327                                 return false;
 328
 329                         var errors_printer = new SessionReportPrinter ();
 330                         var old = bc.Report.SetPrinter (errors_printer);
 331                         ama = new Invocation (ama, args).Resolve (bc);
 332                         bc.Report.SetPrinter (old);
 333
 334                         if (errors_printer.ErrorsCount > 0 || !MemberAccess.IsValidDotExpression (ama.Type)) {
 335                                 bc.Report.Error (1986, expr.Location,
 336                                         "The `await' operand type `{0}' must have suitable GetAwaiter method",
 337                                         expr.Type.GetSignatureForError ());
 338
 339                                 return false;
 340                         }
 341
 342                         var awaiter_type = ama.Type;
 343
 344                         awaiter_definition = bc.Module.GetAwaiter (awaiter_type);
 345
 346                         if (!awaiter_definition.IsValidPattern) {
 347                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 348                                 return false;
 349                         }
 350
 351                         if (!awaiter_definition.INotifyCompletion) {
 352                                 bc.Report.Error (4027, loc, "The awaiter type `{0}' must implement interface `{1}'",
 353                                         awaiter_type.GetSignatureForError (), bc.Module.PredefinedTypes.INotifyCompletion.GetSignatureForError ());
 354                                 return false;
 355                         }
 356
 357                         expr = ama;
 358                         result_type = awaiter_definition.GetResult.ReturnType;
 359
 360                         return true;
 361                 }
 362         }
 363
 364         public class AsyncInitializer : StateMachineInitializer
 365         {
 366                 TypeInferenceContext return_inference;
 367
 368                 public AsyncInitializer (ParametersBlock block, TypeDefinition host, TypeSpec returnType)
 369                         : base (block, host, returnType)
 370                 {
 371                 }
 372
 373                 #region Properties
 374
 375                 public override string ContainerType {
 376                         get {
 377                                 return "async state machine block";
 378                         }
 379                 }
 380
 381                 public override bool IsIterator {
 382                         get {
 383                                 return false;
 384                         }
 385                 }
 386
 387                 public TypeInferenceContext ReturnTypeInference {
 388                         get {
 389                                 return return_inference;
 390                         }
 391                 }
 392
 393                 #endregion
 394
 395                 protected override BlockContext CreateBlockContext (ResolveContext rc)
 396                 {
 397                         var ctx = base.CreateBlockContext (rc);
 398                         var lambda = rc.CurrentAnonymousMethod as LambdaMethod;
 399                         if (lambda != null)
 400                                 return_inference = lambda.ReturnTypeInference;
 401
 402                         ctx.StartFlowBranching (this, rc.CurrentBranching);
 403                         return ctx;
 404                 }
 405
 406                 public override Expression CreateExpressionTree (ResolveContext ec)
 407                 {
 408                         return base.CreateExpressionTree (ec);
 409                 }
 410
 411                 public override void Emit (EmitContext ec)
 412                 {
 413                         throw new NotImplementedException ();
 414                 }
 415
 416                 protected override void EmitMoveNextEpilogue (EmitContext ec)
 417                 {
 418                         var storey = (AsyncTaskStorey) Storey;
 419                         storey.EmitSetResult (ec);
 420                 }
 421
 422                 public override void EmitStatement (EmitContext ec)
 423                 {
 424                         var storey = (AsyncTaskStorey) Storey;
 425                         storey.EmitInitializer (ec);
 426                         ec.Emit (OpCodes.Ret);
 427                 }
 428         }
 429
 430         class AsyncTaskStorey : StateMachine
 431         {
 432                 int awaiters;
 433                 Field builder;
 434                 readonly TypeSpec return_type;
 435                 MethodSpec set_result;
 436                 MethodSpec set_exception;
 437                 MethodSpec builder_factory;
 438                 MethodSpec builder_start;
 439                 PropertySpec task;
 440                 LocalVariable hoisted_return;
 441                 int locals_captured;
 442                 Dictionary<TypeSpec, List<Field>> stack_fields;
 443                 Dictionary<TypeSpec, List<Field>> awaiter_fields;
 444
 445                 public AsyncTaskStorey (ParametersBlock block, IMemberContext context, AsyncInitializer initializer, TypeSpec type)
 446                         : base (block, initializer.Host, context.CurrentMemberDefinition as MemberBase, context.CurrentTypeParameters, "async", MemberKind.Struct)
 447                 {
 448                         return_type = type;
 449                         awaiter_fields = new Dictionary<TypeSpec, List<Field>> ();
 450                 }
 451
 452                 #region Properties
 453
 454                 public LocalVariable HoistedReturn {
 455                         get {
 456                                 return hoisted_return;
 457                         }
 458                 }
 459
 460                 public TypeSpec ReturnType {
 461                         get {
 462                                 return return_type;
 463                         }
 464                 }
 465
 466                 public PropertySpec Task {
 467                         get {
 468                                 return task;
 469                         }
 470                 }
 471
 472                 protected override TypeAttributes TypeAttr {
 473                         get {
 474                                 return base.TypeAttr & ~TypeAttributes.SequentialLayout;
 475                         }
 476                 }
 477
 478                 #endregion
 479
 480                 public Field AddAwaiter (TypeSpec type, Location loc)
 481                 {
 482                         if (mutator != null)
 483                                 type = mutator.Mutate (type);
 484
 485                         List<Field> existing_fields = null;
 486                         if (awaiter_fields.TryGetValue (type, out existing_fields)) {
 487                                 foreach (var f in existing_fields) {
 488                                         if (f.IsAvailableForReuse) {
 489                                                 f.IsAvailableForReuse = false;
 490                                                 return f;
 491                                         }
 492                                 }
 493                         }
 494
 495                         var field = AddCompilerGeneratedField ("$awaiter" + awaiters++.ToString ("X"), new TypeExpression (type, Location), true);
 496                         field.Define ();
 497
 498                         if (existing_fields == null) {
 499                                 existing_fields = new List<Field> ();
 500                                 awaiter_fields.Add (type, existing_fields);
 501                         }
 502
 503                         existing_fields.Add (field);
 504                         return field;
 505                 }
 506
 507                 public Field AddCapturedLocalVariable (TypeSpec type)
 508                 {
 509                         if (mutator != null)
 510                                 type = mutator.Mutate (type);
 511
 512                         List<Field> existing_fields = null;
 513                         if (stack_fields == null) {
 514                                 stack_fields = new Dictionary<TypeSpec, List<Field>> ();
 515                         } else if (stack_fields.TryGetValue (type, out existing_fields)) {
 516                                 foreach (var f in existing_fields) {
 517                                         if (f.IsAvailableForReuse) {
 518                                                 f.IsAvailableForReuse = false;
 519                                                 return f;
 520                                         }
 521                                 }
 522                         }
 523
 524                         var field = AddCompilerGeneratedField ("$stack" + locals_captured++.ToString ("X"), new TypeExpression (type, Location), true);
 525                         field.Define ();
 526
 527                         if (existing_fields == null) {
 528                                 existing_fields = new List<Field> ();
 529                                 stack_fields.Add (type, existing_fields);
 530                         }
 531
 532                         existing_fields.Add (field);
 533
 534                         return field;
 535                 }
 536
 537                 protected override bool DoDefineMembers ()
 538                 {
 539                         PredefinedType builder_type;
 540                         PredefinedMember<MethodSpec> bf;
 541                         PredefinedMember<MethodSpec> bs;
 542                         PredefinedMember<MethodSpec> sr;
 543                         PredefinedMember<MethodSpec> se;
 544                         PredefinedMember<MethodSpec> sm;
 545                         bool has_task_return_type = false;
 546                         var pred_members = Module.PredefinedMembers;
 547
 548                         if (return_type.Kind == MemberKind.Void) {
 549                                 builder_type = Module.PredefinedTypes.AsyncVoidMethodBuilder;
 550                                 bf = pred_members.AsyncVoidMethodBuilderCreate;
 551                                 bs = pred_members.AsyncVoidMethodBuilderStart;
 552                                 sr = pred_members.AsyncVoidMethodBuilderSetResult;
 553                                 se = pred_members.AsyncVoidMethodBuilderSetException;
 554                                 sm = pred_members.AsyncVoidMethodBuilderSetStateMachine;
 555                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 556                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilder;
 557                                 bf = pred_members.AsyncTaskMethodBuilderCreate;
 558                                 bs = pred_members.AsyncTaskMethodBuilderStart;
 559                                 sr = pred_members.AsyncTaskMethodBuilderSetResult;
 560                                 se = pred_members.AsyncTaskMethodBuilderSetException;
 561                                 sm = pred_members.AsyncTaskMethodBuilderSetStateMachine;
 562                                 task = pred_members.AsyncTaskMethodBuilderTask.Get ();
 563                         } else {
 564                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilderGeneric;
 565                                 bf = pred_members.AsyncTaskMethodBuilderGenericCreate;
 566                                 bs = pred_members.AsyncTaskMethodBuilderGenericStart;
 567                                 sr = pred_members.AsyncTaskMethodBuilderGenericSetResult;
 568                                 se = pred_members.AsyncTaskMethodBuilderGenericSetException;
 569                                 sm = pred_members.AsyncTaskMethodBuilderGenericSetStateMachine;
 570                                 task = pred_members.AsyncTaskMethodBuilderGenericTask.Get ();
 571                                 has_task_return_type = true;
 572                         }
 573
 574                         set_result = sr.Get ();
 575                         set_exception = se.Get ();
 576                         builder_factory = bf.Get ();
 577                         builder_start = bs.Get ();
 578
 579                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 580                         var set_statemachine = sm.Get ();
 581
 582                         if (!builder_type.Define () || !istate_machine.Define () || set_result == null || builder_factory == null ||
 583                                 set_exception == null || set_statemachine == null || builder_start == null ||
 584                                 !Module.PredefinedTypes.INotifyCompletion.Define ()) {
 585                                 Report.Error (1993, Location,
 586                                         "Cannot find compiler required types for asynchronous functions support. Are you targeting the wrong framework version?");
 587                                 return base.DoDefineMembers ();
 588                         }
 589
 590                         var bt = builder_type.TypeSpec;
 591
 592                         //
 593                         // Inflate generic Task types
 594                         //
 595                         if (has_task_return_type) {
 596                                 var task_return_type = return_type.TypeArguments;
 597                                 if (mutator != null)
 598                                         task_return_type = mutator.Mutate (task_return_type);
 599
 600                                 bt = bt.MakeGenericType (Module, task_return_type);
 601                                 set_result = MemberCache.GetMember (bt, set_result);
 602                                 set_exception = MemberCache.GetMember (bt, set_exception);
 603                                 set_statemachine = MemberCache.GetMember (bt, set_statemachine);
 604
 605                                 if (task != null)
 606                                         task = MemberCache.GetMember (bt, task);
 607                         }
 608
 609                         builder = AddCompilerGeneratedField ("$builder", new TypeExpression (bt, Location));
 610
 611                         var set_state_machine = new Method (this, new TypeExpression (Compiler.BuiltinTypes.Void, Location),
 612                                 Modifiers.COMPILER_GENERATED | Modifiers.DEBUGGER_HIDDEN | Modifiers.PUBLIC,
 613                                 new MemberName ("SetStateMachine"),
 614                                 ParametersCompiled.CreateFullyResolved (
 615                                         new Parameter (new TypeExpression (istate_machine.TypeSpec, Location), "stateMachine", Parameter.Modifier.NONE, null, Location),
 616                                         istate_machine.TypeSpec),
 617                                 null);
 618
 619                         ToplevelBlock block = new ToplevelBlock (Compiler, set_state_machine.ParameterInfo, Location);
 620                         block.IsCompilerGenerated = true;
 621                         set_state_machine.Block = block;
 622
 623                         Members.Add (set_state_machine);
 624
 625                         if (!base.DoDefineMembers ())
 626                                 return false;
 627
 628                         //
 629                         // Fabricates SetStateMachine method
 630                         //
 631                         // public void SetStateMachine (IAsyncStateMachine stateMachine)
 632                         // {
 633                         //    $builder.SetStateMachine (stateMachine);
 634                         // }
 635                         //
 636                         var mg = MethodGroupExpr.CreatePredefined (set_statemachine, bt, Location);
 637                         mg.InstanceExpression = new FieldExpr (builder, Location);
 638
 639                         var param_reference = block.GetParameterReference (0, Location);
 640                         param_reference.Type = istate_machine.TypeSpec;
 641                         param_reference.eclass = ExprClass.Variable;
 642
 643                         var args = new Arguments (1);
 644                         args.Add (new Argument (param_reference));
 645                         set_state_machine.Block.AddStatement (new StatementExpression (new Invocation (mg, args)));
 646
 647                         if (has_task_return_type) {
 648                                 hoisted_return = LocalVariable.CreateCompilerGenerated (bt.TypeArguments[0], StateMachineMethod.Block, Location);
 649                         }
 650
 651                         return true;
 652                 }
 653
 654                 public void EmitAwaitOnCompletedDynamic (EmitContext ec, FieldExpr awaiter)
 655                 {
 656                         var critical = Module.PredefinedTypes.ICriticalNotifyCompletion;
 657                         if (!critical.Define ()) {
 658                                 throw new NotImplementedException ();
 659                         }
 660
 661                         var temp_critical = new LocalTemporary (critical.TypeSpec);
 662                         var label_critical = ec.DefineLabel ();
 663                         var label_end = ec.DefineLabel ();
 664
 665                         //
 666                         // Special path for dynamic awaiters
 667                         //
 668                         // var awaiter = this.$awaiter as ICriticalNotifyCompletion;
 669                         // if (awaiter == null) {
 670                         //    var completion = (INotifyCompletion) this.$awaiter;
 671                         //    this.$builder.AwaitOnCompleted (ref completion, ref this);
 672                         // } else {
 673                         //    this.$builder.AwaitUnsafeOnCompleted (ref awaiter, ref this);
 674                         // }
 675                         //
 676                         awaiter.Emit (ec);
 677                         ec.Emit (OpCodes.Isinst, critical.TypeSpec);
 678                         temp_critical.Store (ec);
 679                         temp_critical.Emit (ec);
 680                         ec.Emit (OpCodes.Brtrue_S, label_critical);
 681
 682                         var temp = new LocalTemporary (Module.PredefinedTypes.INotifyCompletion.TypeSpec);
 683                         awaiter.Emit (ec);
 684                         ec.Emit (OpCodes.Castclass, temp.Type);
 685                         temp.Store (ec);
 686                         EmitOnCompleted (ec, temp, false);
 687                         temp.Release (ec);
 688                         ec.Emit (OpCodes.Br_S, label_end);
 689
 690                         ec.MarkLabel (label_critical);
 691
 692                         EmitOnCompleted (ec, temp_critical, true);
 693
 694                         ec.MarkLabel (label_end);
 695
 696                         temp_critical.Release (ec);
 697                 }
 698
 699                 public void EmitAwaitOnCompleted (EmitContext ec, FieldExpr awaiter)
 700                 {
 701                         bool unsafe_version = false;
 702                         if (Module.PredefinedTypes.ICriticalNotifyCompletion.Define ()) {
 703                                 unsafe_version = awaiter.Type.ImplementsInterface (Module.PredefinedTypes.ICriticalNotifyCompletion.TypeSpec, false);
 704                         }
 705
 706                         EmitOnCompleted (ec, awaiter, unsafe_version);
 707                 }
 708
 709                 void EmitOnCompleted (EmitContext ec, Expression awaiter, bool unsafeVersion)
 710                 {
 711                         var pm = Module.PredefinedMembers;
 712                         PredefinedMember<MethodSpec> predefined;
 713                         bool has_task_return_type = false;
 714                         if (return_type.Kind == MemberKind.Void) {
 715                                 predefined = unsafeVersion ? pm.AsyncVoidMethodBuilderOnCompletedUnsafe : pm.AsyncVoidMethodBuilderOnCompleted;
 716                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 717                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderOnCompletedUnsafe : pm.AsyncTaskMethodBuilderOnCompleted;
 718                         } else {
 719                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderGenericOnCompletedUnsafe : pm.AsyncTaskMethodBuilderGenericOnCompleted;
 720                                 has_task_return_type = true;
 721                         }
 722
 723                         var on_completed = predefined.Resolve (Location);
 724                         if (on_completed == null)
 725                                 return;
 726
 727                         if (has_task_return_type)
 728                                 on_completed = MemberCache.GetMember<MethodSpec> (set_result.DeclaringType, on_completed);
 729
 730                         on_completed = on_completed.MakeGenericMethod (this, awaiter.Type, ec.CurrentType);
 731
 732                         var mg = MethodGroupExpr.CreatePredefined (on_completed, on_completed.DeclaringType, Location);
 733                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 734                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 735                         };
 736
 737                         var args = new Arguments (2);
 738                         args.Add (new Argument (awaiter, Argument.AType.Ref));
 739                         args.Add (new Argument (new CompilerGeneratedThis (CurrentType, Location), Argument.AType.Ref));
 740                         mg.EmitCall (ec, args);
 741                 }
 742
 743                 public void EmitInitializer (EmitContext ec)
 744                 {
 745                         //
 746                         // Some predefined types are missing
 747                         //
 748                         if (builder == null)
 749                                 return;
 750
 751                         var instance = (TemporaryVariableReference) Instance;
 752                         var builder_field = builder.Spec;
 753                         if (MemberName.Arity > 0) {
 754                                 builder_field = MemberCache.GetMember (instance.Type, builder_field);
 755                         }
 756
 757                         //
 758                         // Inflated factory method when task is of generic type
 759                         //
 760                         if (builder_factory.DeclaringType.IsGeneric) {
 761                                 var task_return_type = return_type.TypeArguments;
 762                                 var bt = builder_factory.DeclaringType.MakeGenericType (Module, task_return_type);
 763                                 builder_factory = MemberCache.GetMember (bt, builder_factory);
 764                                 builder_start = MemberCache.GetMember (bt, builder_start);
 765                         }
 766
 767                         //
 768                         // stateMachine.$builder = AsyncTaskMethodBuilder<{task-type}>.Create();
 769                         //
 770                         instance.AddressOf (ec, AddressOp.Store);
 771                         ec.Emit (OpCodes.Call, builder_factory);
 772                         ec.Emit (OpCodes.Stfld, builder_field);
 773
 774                         //
 775                         // stateMachine.$builder.Start<{storey-type}>(ref stateMachine);
 776                         //
 777                         instance.AddressOf (ec, AddressOp.Store);
 778                         ec.Emit (OpCodes.Ldflda, builder_field);
 779                         if (Task != null)
 780                                 ec.Emit (OpCodes.Dup);
 781                         instance.AddressOf (ec, AddressOp.Store);
 782                         ec.Emit (OpCodes.Call, builder_start.MakeGenericMethod (Module, instance.Type));
 783
 784                         //
 785                         // Emits return stateMachine.$builder.Task;
 786                         //
 787                         if (Task != null) {
 788                                 var task_get = Task.Get;
 789
 790                                 if (MemberName.Arity > 0) {
 791                                         task_get = MemberCache.GetMember (builder_field.MemberType, task_get);
 792                                 }
 793
 794                                 var pe_task = new PropertyExpr (Task, Location) {
 795                                         InstanceExpression = EmptyExpression.Null,      // Comes from the dup above
 796                                         Getter = task_get
 797                                 };
 798
 799                                 pe_task.Emit (ec);
 800                         }
 801                 }
 802
 803                 public void EmitSetException (EmitContext ec, LocalVariableReference exceptionVariable)
 804                 {
 805                         //
 806                         // $builder.SetException (Exception)
 807                         //
 808                         var mg = MethodGroupExpr.CreatePredefined (set_exception, set_exception.DeclaringType, Location);
 809                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 810                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 811                         };
 812
 813                         Arguments args = new Arguments (1);
 814                         args.Add (new Argument (exceptionVariable));
 815
 816                         mg.EmitCall (ec, args);
 817                 }
 818
 819                 public void EmitSetResult (EmitContext ec)
 820                 {
 821                         //
 822                         // $builder.SetResult ();
 823                         // $builder.SetResult<return-type> (value);
 824                         //
 825                         var mg = MethodGroupExpr.CreatePredefined (set_result, set_result.DeclaringType, Location);
 826                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 827                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 828                         };
 829
 830                         Arguments args;
 831                         if (hoisted_return == null) {
 832                                 args = new Arguments (0);
 833                         } else {
 834                                 args = new Arguments (1);
 835                                 args.Add (new Argument (new LocalVariableReference (hoisted_return, Location)));
 836                         }
 837
 838                         mg.EmitCall (ec, args);
 839                 }
 840
 841                 protected override TypeSpec[] ResolveBaseTypes (out FullNamedExpression base_class)
 842                 {
 843                         base_type = Compiler.BuiltinTypes.ValueType;
 844                         base_class = null;
 845
 846                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 847                         if (istate_machine.Define ()) {
 848                                 return new[] { istate_machine.TypeSpec };
 849                         }
 850
 851                         return null;
 852                 }
 853         }
 854
 855         class StackFieldExpr : FieldExpr, IExpressionCleanup
 856         {
 857                 public StackFieldExpr (Field field)
 858                         : base (field, Location.Null)
 859                 {
 860                 }
 861
 862                 public override void AddressOf (EmitContext ec, AddressOp mode)
 863                 {
 864                         base.AddressOf (ec, mode);
 865
 866                         if (mode == AddressOp.Load) {
 867                                 var field = (Field) spec.MemberDefinition;
 868                                 field.IsAvailableForReuse = true;
 869                         }
 870                 }
 871
 872                 public override void Emit (EmitContext ec)
 873                 {
 874                         base.Emit (ec);
 875
 876                         var field = (Field) spec.MemberDefinition;
 877                         field.IsAvailableForReuse = true;
 878
 879                         //
 880                         // Release any captured reference type stack variables
 881                         // to imitate real stack behavour and help GC stuff early
 882                         //
 883                         if (TypeSpec.IsReferenceType (type)) {
 884                                 ec.AddStatementEpilog (this);
 885                         }
 886                 }
 887
 888                 void IExpressionCleanup.EmitCleanup (EmitContext ec)
 889                 {
 890                         EmitAssign (ec, new NullConstant (type, loc), false, false);
 891                 }
 892         }
 893 }