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 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.Emit;
  20 #else
  21 using System.Reflection.Emit;
  22 #endif
  23
  24 namespace Mono.CSharp
  25 {
  26         public class Await : ExpressionStatement
  27         {
  28                 Expression expr;
  29                 AwaitStatement stmt;
  30
  31                 public Await (Expression expr, Location loc)
  32                 {
  33                         this.expr = expr;
  34                         this.loc = loc;
  35                 }
  36
  37                 public Expression Expr {
  38                         get {
  39                                 return expr;
  40                         }
  41                 }
  42
  43                 public AwaitStatement Statement {
  44                         get {
  45                                 return stmt;
  46                         }
  47                 }
  48
  49                 protected override void CloneTo (CloneContext clonectx, Expression target)
  50                 {
  51                         var t = (Await) target;
  52
  53                         t.expr = expr.Clone (clonectx);
  54                 }
  55
  56                 public override Expression CreateExpressionTree (ResolveContext ec)
  57                 {
  58                         throw new NotImplementedException ("ET");
  59                 }
  60
  61                 public override bool ContainsEmitWithAwait ()
  62                 {
  63                         return true;
  64                 }
  65
  66                 protected override Expression DoResolve (ResolveContext rc)
  67                 {
  68                         if (rc.HasSet (ResolveContext.Options.LockScope)) {
  69                                 rc.Report.Error (1996, loc,
  70                                         "The `await' operator cannot be used in the body of a lock statement");
  71                         }
  72
  73                         if (rc.IsUnsafe) {
  74                                 rc.Report.Error (4004, loc,
  75                                         "The `await' operator cannot be used in an unsafe context");
  76                         }
  77
  78                         var bc = (BlockContext) rc;
  79
  80                         stmt = new AwaitStatement (expr, loc);
  81                         if (!stmt.Resolve (bc))
  82                                 return null;
  83
  84                         type = stmt.ResultType;
  85                         eclass = ExprClass.Variable;
  86                         return this;
  87                 }
  88
  89                 public override void Emit (EmitContext ec)
  90                 {
  91                         stmt.EmitPrologue (ec);
  92
  93                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
  94                                 stmt.Emit (ec);
  95                         }
  96                 }
  97
  98                 public override Expression EmitToField (EmitContext ec)
  99                 {
 100                         stmt.EmitPrologue (ec);
 101                         return stmt.GetResultExpression (ec);
 102                 }
 103
 104                 public void EmitAssign (EmitContext ec, FieldExpr field)
 105                 {
 106                         stmt.EmitPrologue (ec);
 107                         field.InstanceExpression.Emit (ec);
 108                         stmt.Emit (ec);
 109                 }
 110
 111                 public override void EmitStatement (EmitContext ec)
 112                 {
 113                         stmt.EmitStatement (ec);
 114                 }
 115
 116                 public override object Accept (StructuralVisitor visitor)
 117                 {
 118                         return visitor.Visit (this);
 119                 }
 120         }
 121
 122         public class AwaitStatement : YieldStatement<AsyncInitializer>
 123         {
 124                 sealed class AwaitableMemberAccess : MemberAccess
 125                 {
 126                         public AwaitableMemberAccess (Expression expr)
 127                                 : base (expr, "GetAwaiter")
 128                         {
 129                         }
 130
 131                         protected override void Error_TypeDoesNotContainDefinition (ResolveContext rc, TypeSpec type, string name)
 132                         {
 133                                 Error_OperatorCannotBeApplied (rc, type);
 134                         }
 135
 136                         protected override void Error_OperatorCannotBeApplied (ResolveContext rc, TypeSpec type)
 137                         {
 138                                 var invocation = LeftExpression as Invocation;
 139                                 if (invocation != null && invocation.MethodGroup != null && (invocation.MethodGroup.BestCandidate.Modifiers & Modifiers.ASYNC) != 0) {
 140                                         rc.Report.Error (4008, loc, "Cannot await void method `{0}'. Consider changing method return type to `Task'",
 141                                                 invocation.GetSignatureForError ());
 142                                 } else {
 143                                         rc.Report.Error (4001, loc, "Cannot await `{0}' expression", type.GetSignatureForError ());
 144                                 }
 145                         }
 146                 }
 147
 148                 sealed class GetResultInvocation : Invocation
 149                 {
 150                         public GetResultInvocation (MethodGroupExpr mge, Arguments arguments)
 151                                 : base (null, arguments)
 152                         {
 153                                 mg = mge;
 154                                 type = mg.BestCandidateReturnType;
 155                         }
 156
 157                         public override Expression EmitToField (EmitContext ec)
 158                         {
 159                                 return this;
 160                         }
 161                 }
 162
 163                 Field awaiter;
 164                 PropertySpec is_completed;
 165                 MethodSpec get_result;
 166                 TypeSpec type;
 167                 TypeSpec result_type;
 168
 169                 public AwaitStatement (Expression expr, Location loc)
 170                         : base (expr, loc)
 171                 {
 172                 }
 173
 174                 #region Properties
 175
 176                 bool IsDynamic {
 177                         get {
 178                                 return is_completed == null;
 179                         }
 180                 }
 181
 182                 public TypeSpec ResultType {
 183                         get {
 184                                 return result_type;
 185                         }
 186                 }
 187
 188                 #endregion
 189
 190                 protected override void DoEmit (EmitContext ec)
 191                 {
 192                         GetResultExpression (ec).Emit (ec);
 193                 }
 194
 195                 public Expression GetResultExpression (EmitContext ec)
 196                 {
 197                         var fe_awaiter = new FieldExpr (awaiter, loc);
 198                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 199
 200                         //
 201                         // result = awaiter.GetResult ();
 202                         //
 203                         if (IsDynamic) {
 204                                 var rc = new ResolveContext (ec.MemberContext);
 205                                 return new Invocation (new MemberAccess (fe_awaiter, "GetResult"), new Arguments (0)).Resolve (rc);
 206                         } else {
 207                                 var mg_result = MethodGroupExpr.CreatePredefined (get_result, fe_awaiter.Type, loc);
 208                                 mg_result.InstanceExpression = fe_awaiter;
 209
 210                                 return new GetResultInvocation (mg_result, new Arguments (0));
 211                         }
 212                 }
 213
 214                 public void EmitPrologue (EmitContext ec)
 215                 {
 216                         awaiter = ((AsyncTaskStorey) machine_initializer.Storey).AddAwaiter (expr.Type, loc);
 217
 218                         var fe_awaiter = new FieldExpr (awaiter, loc);
 219                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 220
 221                         //
 222                         // awaiter = expr.GetAwaiter ();
 223                         //
 224                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 225                                 fe_awaiter.EmitAssign (ec, expr, false, false);
 226                         }
 227
 228                         Label skip_continuation = ec.DefineLabel ();
 229
 230                         Expression completed_expr;
 231                         if (IsDynamic) {
 232                                 var rc = new ResolveContext (ec.MemberContext);
 233
 234                                 Arguments dargs = new Arguments (1);
 235                                 dargs.Add (new Argument (fe_awaiter));
 236                                 completed_expr = new DynamicMemberBinder ("IsCompleted", dargs, loc).Resolve (rc);
 237
 238                                 dargs = new Arguments (1);
 239                                 dargs.Add (new Argument (completed_expr));
 240                                 completed_expr = new DynamicConversion (ec.Module.Compiler.BuiltinTypes.Bool, 0, dargs, loc).Resolve (rc);
 241                         } else {
 242                                 var pe = PropertyExpr.CreatePredefined (is_completed, loc);
 243                                 pe.InstanceExpression = fe_awaiter;
 244                                 completed_expr = pe;
 245                         }
 246
 247                         completed_expr.EmitBranchable (ec, skip_continuation, true);
 248
 249                         base.DoEmit (ec);
 250
 251                         //
 252                         // The stack has to be empty before calling await continuation. We handle this
 253                         // by lifting values which would be left on stack into class fields. The process
 254                         // is quite complicated and quite hard to test because any expression can possibly
 255                         // leave a value on the stack.
 256                         //
 257                         // Following assert fails when some of expression called before is missing EmitToField
 258                         // or parent expression fails to find await in children expressions
 259                         //
 260                         ec.AssertEmptyStack ();
 261
 262                         var storey = (AsyncTaskStorey) machine_initializer.Storey;
 263                         if (IsDynamic) {
 264                                 storey.EmitAwaitOnCompletedDynamic (ec, fe_awaiter);
 265                         } else {
 266                                 storey.EmitAwaitOnCompleted (ec, fe_awaiter);
 267                         }
 268
 269                         // Return ok
 270                         machine_initializer.EmitLeave (ec, unwind_protect);
 271
 272                         ec.MarkLabel (resume_point);
 273                         ec.MarkLabel (skip_continuation);
 274                 }
 275
 276                 public void EmitStatement (EmitContext ec)
 277                 {
 278                         EmitPrologue (ec);
 279                         DoEmit (ec);
 280
 281                         awaiter.IsAvailableForReuse = true;
 282
 283                         if (ResultType.Kind != MemberKind.Void)
 284                                 ec.Emit (OpCodes.Pop);
 285                 }
 286
 287                 void Error_WrongAwaiterPattern (ResolveContext rc, TypeSpec awaiter)
 288                 {
 289                         rc.Report.Error (4011, loc, "The awaiter type `{0}' must have suitable IsCompleted and GetResult members",
 290                                 awaiter.GetSignatureForError ());
 291                 }
 292
 293                 public override bool Resolve (BlockContext bc)
 294                 {
 295                         if (bc.CurrentBlock is Linq.QueryBlock) {
 296                                 bc.Report.Error (1995, loc,
 297                                         "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");
 298                                 return false;
 299                         }
 300
 301                         if (!base.Resolve (bc))
 302                                 return false;
 303
 304                         Arguments args = new Arguments (0);
 305
 306                         type = expr.Type;
 307
 308                         //
 309                         // The await expression is of dynamic type
 310                         //
 311                         if (type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 312                                 result_type = type;
 313                                 expr = new Invocation (new MemberAccess (expr, "GetAwaiter"), args).Resolve (bc);
 314                                 return true;
 315                         }
 316
 317                         //
 318                         // Check whether the expression is awaitable
 319                         //
 320                         Expression ama = new AwaitableMemberAccess (expr).Resolve (bc);
 321                         if (ama == null)
 322                                 return false;
 323
 324                         var errors_printer = new SessionReportPrinter ();
 325                         var old = bc.Report.SetPrinter (errors_printer);
 326                         ama = new Invocation (ama, args).Resolve (bc);
 327                         bc.Report.SetPrinter (old);
 328
 329                         if (errors_printer.ErrorsCount > 0 || !MemberAccess.IsValidDotExpression (ama.Type)) {
 330                                 bc.Report.Error (1986, expr.Location,
 331                                         "The `await' operand type `{0}' must have suitable GetAwaiter method",
 332                                         expr.Type.GetSignatureForError ());
 333
 334                                 return false;
 335                         }
 336
 337                         var awaiter_type = ama.Type;
 338                         expr = ama;
 339
 340                         //
 341                         // Predefined: bool IsCompleted { get; }
 342                         //
 343                         is_completed = MemberCache.FindMember (awaiter_type, MemberFilter.Property ("IsCompleted", bc.Module.Compiler.BuiltinTypes.Bool),
 344                                 BindingRestriction.InstanceOnly) as PropertySpec;
 345
 346                         if (is_completed == null || !is_completed.HasGet) {
 347                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 348                                 return false;
 349                         }
 350
 351                         //
 352                         // Predefined: GetResult ()
 353                         //
 354                         // The method return type is also result type of await expression
 355                         //
 356                         get_result = MemberCache.FindMember (awaiter_type, MemberFilter.Method ("GetResult", 0,
 357                                 ParametersCompiled.EmptyReadOnlyParameters, null),
 358                                 BindingRestriction.InstanceOnly) as MethodSpec;
 359
 360                         if (get_result == null) {
 361                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 362                                 return false;
 363                         }
 364
 365                         //
 366                         // Predefined: INotifyCompletion.OnCompleted (System.Action)
 367                         //
 368                         var nc = bc.Module.PredefinedTypes.INotifyCompletion;
 369                         if (nc.Define () && !awaiter_type.ImplementsInterface (nc.TypeSpec, false)) {
 370                                 bc.Report.Error (4027, loc, "The awaiter type `{0}' must implement interface `{1}'",
 371                                         awaiter_type.GetSignatureForError (), nc.GetSignatureForError ());
 372                                 return false;
 373                         }
 374
 375                         result_type = get_result.ReturnType;
 376
 377                         return true;
 378                 }
 379         }
 380
 381         public class AsyncInitializer : StateMachineInitializer
 382         {
 383                 TypeInferenceContext return_inference;
 384
 385                 public AsyncInitializer (ParametersBlock block, TypeDefinition host, TypeSpec returnType)
 386                         : base (block, host, returnType)
 387                 {
 388                 }
 389
 390                 #region Properties
 391
 392                 public override string ContainerType {
 393                         get {
 394                                 return "async state machine block";
 395                         }
 396                 }
 397
 398                 public override bool IsIterator {
 399                         get {
 400                                 return false;
 401                         }
 402                 }
 403
 404                 public TypeInferenceContext ReturnTypeInference {
 405                         get {
 406                                 return return_inference;
 407                         }
 408                 }
 409
 410                 #endregion
 411
 412                 protected override BlockContext CreateBlockContext (ResolveContext rc)
 413                 {
 414                         var ctx = base.CreateBlockContext (rc);
 415                         var lambda = rc.CurrentAnonymousMethod as LambdaMethod;
 416                         if (lambda != null)
 417                                 return_inference = lambda.ReturnTypeInference;
 418
 419                         ctx.StartFlowBranching (this, rc.CurrentBranching);
 420                         return ctx;
 421                 }
 422
 423                 public override Expression CreateExpressionTree (ResolveContext ec)
 424                 {
 425                         return base.CreateExpressionTree (ec);
 426                 }
 427
 428                 public override void Emit (EmitContext ec)
 429                 {
 430                         throw new NotImplementedException ();
 431                 }
 432
 433                 protected override void EmitMoveNextEpilogue (EmitContext ec)
 434                 {
 435                         var storey = (AsyncTaskStorey) Storey;
 436                         storey.EmitSetResult (ec);
 437                 }
 438
 439                 public override void EmitStatement (EmitContext ec)
 440                 {
 441                         var storey = (AsyncTaskStorey) Storey;
 442                         storey.EmitInitializer (ec);
 443                         ec.Emit (OpCodes.Ret);
 444                 }
 445         }
 446
 447         class AsyncTaskStorey : StateMachine
 448         {
 449                 int awaiters;
 450                 Field builder;
 451                 readonly TypeSpec return_type;
 452                 MethodSpec set_result;
 453                 MethodSpec set_exception;
 454                 MethodSpec builder_factory;
 455                 MethodSpec builder_start;
 456                 PropertySpec task;
 457                 LocalVariable hoisted_return;
 458                 int locals_captured;
 459                 Dictionary<TypeSpec, List<Field>> stack_fields;
 460                 Dictionary<TypeSpec, List<Field>> awaiter_fields;
 461
 462                 public AsyncTaskStorey (ParametersBlock block, IMemberContext context, AsyncInitializer initializer, TypeSpec type)
 463                         : base (block, initializer.Host, context.CurrentMemberDefinition as MemberBase, context.CurrentTypeParameters, "async", MemberKind.Struct)
 464                 {
 465                         return_type = type;
 466                         awaiter_fields = new Dictionary<TypeSpec, List<Field>> ();
 467                 }
 468
 469                 #region Properties
 470
 471                 public LocalVariable HoistedReturn {
 472                         get {
 473                                 return hoisted_return;
 474                         }
 475                 }
 476
 477                 public TypeSpec ReturnType {
 478                         get {
 479                                 return return_type;
 480                         }
 481                 }
 482
 483                 public PropertySpec Task {
 484                         get {
 485                                 return task;
 486                         }
 487                 }
 488
 489                 #endregion
 490
 491                 public Field AddAwaiter (TypeSpec type, Location loc)
 492                 {
 493                         if (mutator != null)
 494                                 type = mutator.Mutate (type);
 495
 496                         List<Field> existing_fields = null;
 497                         if (awaiter_fields.TryGetValue (type, out existing_fields)) {
 498                                 foreach (var f in existing_fields) {
 499                                         if (f.IsAvailableForReuse) {
 500                                                 f.IsAvailableForReuse = false;
 501                                                 return f;
 502                                         }
 503                                 }
 504                         }
 505
 506                         var field = AddCompilerGeneratedField ("$awaiter" + awaiters++.ToString ("X"), new TypeExpression (type, Location), true);
 507                         field.Define ();
 508
 509                         if (existing_fields == null) {
 510                                 existing_fields = new List<Field> ();
 511                                 awaiter_fields.Add (type, existing_fields);
 512                         }
 513
 514                         existing_fields.Add (field);
 515                         return field;
 516                 }
 517
 518                 public Field AddCapturedLocalVariable (TypeSpec type)
 519                 {
 520                         if (mutator != null)
 521                                 type = mutator.Mutate (type);
 522
 523                         List<Field> existing_fields = null;
 524                         if (stack_fields == null) {
 525                                 stack_fields = new Dictionary<TypeSpec, List<Field>> ();
 526                         } else if (stack_fields.TryGetValue (type, out existing_fields)) {
 527                                 foreach (var f in existing_fields) {
 528                                         if (f.IsAvailableForReuse) {
 529                                                 f.IsAvailableForReuse = false;
 530                                                 return f;
 531                                         }
 532                                 }
 533                         }
 534
 535                         var field = AddCompilerGeneratedField ("$stack" + locals_captured++.ToString ("X"), new TypeExpression (type, Location), true);
 536                         field.Define ();
 537
 538                         if (existing_fields == null) {
 539                                 existing_fields = new List<Field> ();
 540                                 stack_fields.Add (type, existing_fields);
 541                         }
 542
 543                         existing_fields.Add (field);
 544
 545                         return field;
 546                 }
 547
 548                 protected override bool DoDefineMembers ()
 549                 {
 550                         PredefinedType builder_type;
 551                         PredefinedMember<MethodSpec> bf;
 552                         PredefinedMember<MethodSpec> bs;
 553                         PredefinedMember<MethodSpec> sr;
 554                         PredefinedMember<MethodSpec> se;
 555                         PredefinedMember<MethodSpec> sm;
 556                         bool has_task_return_type = false;
 557                         var pred_members = Module.PredefinedMembers;
 558
 559                         if (return_type.Kind == MemberKind.Void) {
 560                                 builder_type = Module.PredefinedTypes.AsyncVoidMethodBuilder;
 561                                 bf = pred_members.AsyncVoidMethodBuilderCreate;
 562                                 bs = pred_members.AsyncVoidMethodBuilderStart;
 563                                 sr = pred_members.AsyncVoidMethodBuilderSetResult;
 564                                 se = pred_members.AsyncVoidMethodBuilderSetException;
 565                                 sm = pred_members.AsyncVoidMethodBuilderSetStateMachine;
 566                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 567                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilder;
 568                                 bf = pred_members.AsyncTaskMethodBuilderCreate;
 569                                 bs = pred_members.AsyncTaskMethodBuilderStart;
 570                                 sr = pred_members.AsyncTaskMethodBuilderSetResult;
 571                                 se = pred_members.AsyncTaskMethodBuilderSetException;
 572                                 sm = pred_members.AsyncTaskMethodBuilderSetStateMachine;
 573                                 task = pred_members.AsyncTaskMethodBuilderTask.Get ();
 574                         } else {
 575                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilderGeneric;
 576                                 bf = pred_members.AsyncTaskMethodBuilderGenericCreate;
 577                                 bs = pred_members.AsyncTaskMethodBuilderGenericStart;
 578                                 sr = pred_members.AsyncTaskMethodBuilderGenericSetResult;
 579                                 se = pred_members.AsyncTaskMethodBuilderGenericSetException;
 580                                 sm = pred_members.AsyncTaskMethodBuilderGenericSetStateMachine;
 581                                 task = pred_members.AsyncTaskMethodBuilderGenericTask.Get ();
 582                                 has_task_return_type = true;
 583                         }
 584
 585                         set_result = sr.Get ();
 586                         set_exception = se.Get ();
 587                         builder_factory = bf.Get ();
 588                         builder_start = bs.Get ();
 589
 590                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 591                         var set_statemachine = sm.Get ();
 592
 593                         if (!builder_type.Define () || !istate_machine.Define () || set_result == null || builder_factory == null ||
 594                                 set_exception == null || set_statemachine == null || builder_start == null ||
 595                                 !Module.PredefinedTypes.INotifyCompletion.Define ()) {
 596                                 Report.Error (1993, Location,
 597                                         "Cannot find compiler required types for asynchronous functions support. Are you targeting the wrong framework version?");
 598                                 return base.DoDefineMembers ();
 599                         }
 600
 601                         var bt = builder_type.TypeSpec;
 602
 603                         //
 604                         // Inflate generic Task types
 605                         //
 606                         if (has_task_return_type) {
 607                                 var task_return_type = return_type.TypeArguments;
 608                                 if (mutator != null)
 609                                         task_return_type = mutator.Mutate (task_return_type);
 610
 611                                 bt = bt.MakeGenericType (Module, task_return_type);
 612                                 set_result = MemberCache.GetMember (bt, set_result);
 613                                 set_exception = MemberCache.GetMember (bt, set_exception);
 614                                 set_statemachine = MemberCache.GetMember (bt, set_statemachine);
 615
 616                                 if (task != null)
 617                                         task = MemberCache.GetMember (bt, task);
 618                         }
 619
 620                         builder = AddCompilerGeneratedField ("$builder", new TypeExpression (bt, Location));
 621
 622                         var set_state_machine = new Method (this, new TypeExpression (Compiler.BuiltinTypes.Void, Location),
 623                                 Modifiers.COMPILER_GENERATED | Modifiers.DEBUGGER_HIDDEN | Modifiers.PUBLIC,
 624                                 new MemberName ("SetStateMachine"),
 625                                 ParametersCompiled.CreateFullyResolved (
 626                                         new Parameter (new TypeExpression (istate_machine.TypeSpec, Location), "stateMachine", Parameter.Modifier.NONE, null, Location),
 627                                         istate_machine.TypeSpec),
 628                                 null);
 629
 630                         ToplevelBlock block = new ToplevelBlock (Compiler, set_state_machine.ParameterInfo, Location);
 631                         block.IsCompilerGenerated = true;
 632                         set_state_machine.Block = block;
 633
 634                         Members.Add (set_state_machine);
 635
 636                         if (!base.DoDefineMembers ())
 637                                 return false;
 638
 639                         //
 640                         // Fabricates SetStateMachine method
 641                         //
 642                         // public void SetStateMachine (IAsyncStateMachine stateMachine)
 643                         // {
 644                         //    $builder.SetStateMachine (stateMachine);
 645                         // }
 646                         //
 647                         var mg = MethodGroupExpr.CreatePredefined (set_statemachine, bt, Location);
 648                         mg.InstanceExpression = new FieldExpr (builder, Location);
 649
 650                         var param_reference = block.GetParameterReference (0, Location);
 651                         param_reference.Type = istate_machine.TypeSpec;
 652                         param_reference.eclass = ExprClass.Variable;
 653
 654                         var args = new Arguments (1);
 655                         args.Add (new Argument (param_reference));
 656                         set_state_machine.Block.AddStatement (new StatementExpression (new Invocation (mg, args)));
 657
 658                         if (has_task_return_type) {
 659                                 hoisted_return = LocalVariable.CreateCompilerGenerated (bt.TypeArguments[0], StateMachineMethod.Block, Location);
 660                         }
 661
 662                         return true;
 663                 }
 664
 665                 public void EmitAwaitOnCompletedDynamic (EmitContext ec, FieldExpr awaiter)
 666                 {
 667                         var critical = Module.PredefinedTypes.ICriticalNotifyCompletion;
 668                         if (!critical.Define ()) {
 669                                 throw new NotImplementedException ();
 670                         }
 671
 672                         var temp_critical = new LocalTemporary (critical.TypeSpec);
 673                         var label_critical = ec.DefineLabel ();
 674                         var label_end = ec.DefineLabel ();
 675
 676                         //
 677                         // Special path for dynamic awaiters
 678                         //
 679                         // var awaiter = this.$awaiter as ICriticalNotifyCompletion;
 680                         // if (awaiter == null) {
 681                         //    var completion = (INotifyCompletion) this.$awaiter;
 682                         //    this.$builder.AwaitOnCompleted (ref completion, ref this);
 683                         // } else {
 684                         //    this.$builder.AwaitUnsafeOnCompleted (ref awaiter, ref this);
 685                         // }
 686                         //
 687                         awaiter.Emit (ec);
 688                         ec.Emit (OpCodes.Isinst, critical.TypeSpec);
 689                         temp_critical.Store (ec);
 690                         temp_critical.Emit (ec);
 691                         ec.Emit (OpCodes.Brtrue_S, label_critical);
 692
 693                         var temp = new LocalTemporary (Module.PredefinedTypes.INotifyCompletion.TypeSpec);
 694                         awaiter.Emit (ec);
 695                         ec.Emit (OpCodes.Castclass, temp.Type);
 696                         temp.Store (ec);
 697                         EmitOnCompleted (ec, temp, false);
 698                         temp.Release (ec);
 699                         ec.Emit (OpCodes.Br_S, label_end);
 700
 701                         ec.MarkLabel (label_critical);
 702
 703                         EmitOnCompleted (ec, temp_critical, true);
 704
 705                         ec.MarkLabel (label_end);
 706
 707                         temp_critical.Release (ec);
 708                 }
 709
 710                 public void EmitAwaitOnCompleted (EmitContext ec, FieldExpr awaiter)
 711                 {
 712                         bool unsafe_version = false;
 713                         if (Module.PredefinedTypes.ICriticalNotifyCompletion.Define ()) {
 714                                 unsafe_version = awaiter.Type.ImplementsInterface (Module.PredefinedTypes.ICriticalNotifyCompletion.TypeSpec, false);
 715                         }
 716
 717                         EmitOnCompleted (ec, awaiter, unsafe_version);
 718                 }
 719
 720                 void EmitOnCompleted (EmitContext ec, Expression awaiter, bool unsafeVersion)
 721                 {
 722                         var pm = Module.PredefinedMembers;
 723                         PredefinedMember<MethodSpec> predefined;
 724                         bool has_task_return_type = false;
 725                         if (return_type.Kind == MemberKind.Void) {
 726                                 predefined = unsafeVersion ? pm.AsyncVoidMethodBuilderOnCompletedUnsafe : pm.AsyncVoidMethodBuilderOnCompleted;
 727                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 728                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderOnCompletedUnsafe : pm.AsyncTaskMethodBuilderOnCompleted;
 729                         } else {
 730                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderGenericOnCompletedUnsafe : pm.AsyncTaskMethodBuilderGenericOnCompleted;
 731                                 has_task_return_type = true;
 732                         }
 733
 734                         var on_completed = predefined.Resolve (Location);
 735                         if (on_completed == null)
 736                                 return;
 737
 738                         if (has_task_return_type)
 739                                 on_completed = MemberCache.GetMember<MethodSpec> (set_result.DeclaringType, on_completed);
 740
 741                         on_completed = on_completed.MakeGenericMethod (this, awaiter.Type, ec.CurrentType);
 742
 743                         var mg = MethodGroupExpr.CreatePredefined (on_completed, on_completed.DeclaringType, Location);
 744                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 745                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 746                         };
 747
 748                         var args = new Arguments (2);
 749                         args.Add (new Argument (awaiter, Argument.AType.Ref));
 750                         args.Add (new Argument (new CompilerGeneratedThis (CurrentType, Location), Argument.AType.Ref));
 751                         mg.EmitCall (ec, args);
 752                 }
 753
 754                 public void EmitInitializer (EmitContext ec)
 755                 {
 756                         //
 757                         // Some predefined types are missing
 758                         //
 759                         if (builder == null)
 760                                 return;
 761
 762                         var instance = (TemporaryVariableReference) Instance;
 763                         var builder_field = builder.Spec;
 764                         if (MemberName.Arity > 0) {
 765                                 builder_field = MemberCache.GetMember (instance.Type, builder_field);
 766                         }
 767
 768                         //
 769                         // Inflated factory method when task is of generic type
 770                         //
 771                         if (builder_factory.DeclaringType.IsGeneric) {
 772                                 var task_return_type = return_type.TypeArguments;
 773                                 var bt = builder_factory.DeclaringType.MakeGenericType (Module, task_return_type);
 774                                 builder_factory = MemberCache.GetMember (bt, builder_factory);
 775                                 builder_start = MemberCache.GetMember (bt, builder_start);
 776                         }
 777
 778                         //
 779                         // stateMachine.$builder = AsyncTaskMethodBuilder<{task-type}>.Create();
 780                         //
 781                         instance.AddressOf (ec, AddressOp.Store);
 782                         ec.Emit (OpCodes.Call, builder_factory);
 783                         ec.Emit (OpCodes.Stfld, builder_field);
 784
 785                         //
 786                         // stateMachine.$builder.Start<{storey-type}>(ref stateMachine);
 787                         //
 788                         instance.AddressOf (ec, AddressOp.Store);
 789                         ec.Emit (OpCodes.Ldflda, builder_field);
 790                         if (Task != null)
 791                                 ec.Emit (OpCodes.Dup);
 792                         instance.AddressOf (ec, AddressOp.Store);
 793                         ec.Emit (OpCodes.Call, builder_start.MakeGenericMethod (Module, instance.Type));
 794
 795                         //
 796                         // Emits return stateMachine.$builder.Task;
 797                         //
 798                         if (Task != null) {
 799                                 var task_get = Task.Get;
 800
 801                                 if (MemberName.Arity > 0) {
 802                                         task_get = MemberCache.GetMember (builder_field.MemberType, task_get);
 803                                 }
 804
 805                                 var pe_task = new PropertyExpr (Task, Location) {
 806                                         InstanceExpression = EmptyExpression.Null,      // Comes from the dup above
 807                                         Getter = task_get
 808                                 };
 809
 810                                 pe_task.Emit (ec);
 811                         }
 812                 }
 813
 814                 public void EmitSetException (EmitContext ec, LocalVariableReference exceptionVariable)
 815                 {
 816                         //
 817                         // $builder.SetException (Exception)
 818                         //
 819                         var mg = MethodGroupExpr.CreatePredefined (set_exception, set_exception.DeclaringType, Location);
 820                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 821                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 822                         };
 823
 824                         Arguments args = new Arguments (1);
 825                         args.Add (new Argument (exceptionVariable));
 826
 827                         mg.EmitCall (ec, args);
 828                 }
 829
 830                 public void EmitSetResult (EmitContext ec)
 831                 {
 832                         //
 833                         // $builder.SetResult ();
 834                         // $builder.SetResult<return-type> (value);
 835                         //
 836                         var mg = MethodGroupExpr.CreatePredefined (set_result, set_result.DeclaringType, Location);
 837                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 838                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 839                         };
 840
 841                         Arguments args;
 842                         if (hoisted_return == null) {
 843                                 args = new Arguments (0);
 844                         } else {
 845                                 args = new Arguments (1);
 846                                 args.Add (new Argument (new LocalVariableReference (hoisted_return, Location)));
 847                         }
 848
 849                         mg.EmitCall (ec, args);
 850                 }
 851
 852                 protected override TypeSpec[] ResolveBaseTypes (out FullNamedExpression base_class)
 853                 {
 854                         base_type = Compiler.BuiltinTypes.ValueType;
 855                         base_class = null;
 856
 857                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 858                         if (istate_machine.Define ()) {
 859                                 return new[] { istate_machine.TypeSpec };
 860                         }
 861
 862                         return null;
 863                 }
 864         }
 865
 866         class StackFieldExpr : FieldExpr, IExpressionCleanup
 867         {
 868                 public StackFieldExpr (Field field)
 869                         : base (field, Location.Null)
 870                 {
 871                 }
 872
 873                 public override void AddressOf (EmitContext ec, AddressOp mode)
 874                 {
 875                         base.AddressOf (ec, mode);
 876
 877                         if (mode == AddressOp.Load) {
 878                                 var field = (Field) spec.MemberDefinition;
 879                                 field.IsAvailableForReuse = true;
 880                         }
 881                 }
 882
 883                 public override void Emit (EmitContext ec)
 884                 {
 885                         base.Emit (ec);
 886
 887                         var field = (Field) spec.MemberDefinition;
 888                         field.IsAvailableForReuse = true;
 889
 890                         //
 891                         // Release any captured reference type stack variables
 892                         // to imitate real stack behavour and help GC stuff early
 893                         //
 894                         if (TypeSpec.IsReferenceType (type)) {
 895                                 ec.AddStatementEpilog (this);
 896                         }
 897                 }
 898
 899                 void IExpressionCleanup.EmitCleanup (EmitContext ec)
 900                 {
 901                         EmitAssign (ec, new NullConstant (type, loc), false, false);
 902                 }
 903         }
 904 }