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                         fe_awaiter.EmitAssign (ec, expr, false, false);
 225
 226                         Label skip_continuation = ec.DefineLabel ();
 227
 228                         Expression completed_expr;
 229                         if (IsDynamic) {
 230                                 var rc = new ResolveContext (ec.MemberContext);
 231
 232                                 Arguments dargs = new Arguments (1);
 233                                 dargs.Add (new Argument (fe_awaiter));
 234                                 completed_expr = new DynamicMemberBinder ("IsCompleted", dargs, loc).Resolve (rc);
 235
 236                                 dargs = new Arguments (1);
 237                                 dargs.Add (new Argument (completed_expr));
 238                                 completed_expr = new DynamicConversion (ec.Module.Compiler.BuiltinTypes.Bool, 0, dargs, loc).Resolve (rc);
 239                         } else {
 240                                 var pe = PropertyExpr.CreatePredefined (is_completed, loc);
 241                                 pe.InstanceExpression = fe_awaiter;
 242                                 completed_expr = pe;
 243                         }
 244
 245                         completed_expr.EmitBranchable (ec, skip_continuation, true);
 246
 247                         base.DoEmit (ec);
 248
 249                         //
 250                         // The stack has to be empty before calling await continuation. We handle this
 251                         // by lifting values which would be left on stack into class fields. The process
 252                         // is quite complicated and quite hard to test because any expression can possibly
 253                         // leave a value on the stack.
 254                         //
 255                         // Following assert fails when some of expression called before is missing EmitToField
 256                         // or parent expression fails to find await in children expressions
 257                         //
 258                         ec.AssertEmptyStack ();
 259
 260                         var storey = (AsyncTaskStorey) machine_initializer.Storey;
 261                         if (IsDynamic) {
 262                                 storey.EmitAwaitOnCompletedDynamic (ec, fe_awaiter);
 263                         } else {
 264                                 storey.EmitAwaitOnCompleted (ec, fe_awaiter);
 265                         }
 266
 267                         // Return ok
 268                         machine_initializer.EmitLeave (ec, unwind_protect);
 269
 270                         ec.MarkLabel (resume_point);
 271                         ec.MarkLabel (skip_continuation);
 272                 }
 273
 274                 public void EmitStatement (EmitContext ec)
 275                 {
 276                         EmitPrologue (ec);
 277                         DoEmit (ec);
 278
 279                         awaiter.IsAvailableForReuse = true;
 280
 281                         if (ResultType.Kind != MemberKind.Void) {
 282                                 var storey = (AsyncTaskStorey) machine_initializer.Storey;
 283
 284                             if (storey.HoistedReturn != null)
 285                                 storey.HoistedReturn.EmitAssign (ec);
 286                                 else
 287                                         ec.Emit (OpCodes.Pop);
 288                         }
 289                 }
 290
 291                 void Error_WrongAwaiterPattern (ResolveContext rc, TypeSpec awaiter)
 292                 {
 293                         rc.Report.Error (4011, loc, "The awaiter type `{0}' must have suitable IsCompleted and GetResult members",
 294                                 awaiter.GetSignatureForError ());
 295                 }
 296
 297                 public override bool Resolve (BlockContext bc)
 298                 {
 299                         if (bc.CurrentBlock is Linq.QueryBlock) {
 300                                 bc.Report.Error (1995, loc,
 301                                         "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");
 302                                 return false;
 303                         }
 304
 305                         if (!base.Resolve (bc))
 306                                 return false;
 307
 308                         Arguments args = new Arguments (0);
 309
 310                         type = expr.Type;
 311
 312                         //
 313                         // The await expression is of dynamic type
 314                         //
 315                         if (type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 316                                 result_type = type;
 317                                 expr = new Invocation (new MemberAccess (expr, "GetAwaiter"), args).Resolve (bc);
 318                                 return true;
 319                         }
 320
 321                         //
 322                         // Check whether the expression is awaitable
 323                         //
 324                         Expression ama = new AwaitableMemberAccess (expr).Resolve (bc);
 325                         if (ama == null)
 326                                 return false;
 327
 328                         var errors_printer = new SessionReportPrinter ();
 329                         var old = bc.Report.SetPrinter (errors_printer);
 330                         ama = new Invocation (ama, args).Resolve (bc);
 331                         bc.Report.SetPrinter (old);
 332
 333                         if (errors_printer.ErrorsCount > 0 || !MemberAccess.IsValidDotExpression (ama.Type)) {
 334                                 bc.Report.Error (1986, expr.Location,
 335                                         "The `await' operand type `{0}' must have suitable GetAwaiter method",
 336                                         expr.Type.GetSignatureForError ());
 337
 338                                 return false;
 339                         }
 340
 341                         var awaiter_type = ama.Type;
 342                         expr = ama;
 343
 344                         //
 345                         // Predefined: bool IsCompleted { get; }
 346                         //
 347                         is_completed = MemberCache.FindMember (awaiter_type, MemberFilter.Property ("IsCompleted", bc.Module.Compiler.BuiltinTypes.Bool),
 348                                 BindingRestriction.InstanceOnly) as PropertySpec;
 349
 350                         if (is_completed == null || !is_completed.HasGet) {
 351                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 352                                 return false;
 353                         }
 354
 355                         //
 356                         // Predefined: GetResult ()
 357                         //
 358                         // The method return type is also result type of await expression
 359                         //
 360                         get_result = MemberCache.FindMember (awaiter_type, MemberFilter.Method ("GetResult", 0,
 361                                 ParametersCompiled.EmptyReadOnlyParameters, null),
 362                                 BindingRestriction.InstanceOnly) as MethodSpec;
 363
 364                         if (get_result == null) {
 365                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 366                                 return false;
 367                         }
 368
 369                         //
 370                         // Predefined: INotifyCompletion.OnCompleted (System.Action)
 371                         //
 372                         var nc = bc.Module.PredefinedTypes.INotifyCompletion;
 373                         if (nc.Define () && !awaiter_type.ImplementsInterface (nc.TypeSpec, false)) {
 374                                 bc.Report.Error (4027, loc, "The awaiter type `{0}' must implement interface `{1}'",
 375                                         awaiter_type.GetSignatureForError (), nc.GetSignatureForError ());
 376                                 return false;
 377                         }
 378
 379                         result_type = get_result.ReturnType;
 380
 381                         return true;
 382                 }
 383         }
 384
 385         public class AsyncInitializer : StateMachineInitializer
 386         {
 387                 TypeInferenceContext return_inference;
 388
 389                 public AsyncInitializer (ParametersBlock block, TypeDefinition host, TypeSpec returnType)
 390                         : base (block, host, returnType)
 391                 {
 392                 }
 393
 394                 #region Properties
 395
 396                 public override string ContainerType {
 397                         get {
 398                                 return "async state machine block";
 399                         }
 400                 }
 401
 402                 public override bool IsIterator {
 403                         get {
 404                                 return false;
 405                         }
 406                 }
 407
 408                 public TypeInferenceContext ReturnTypeInference {
 409                         get {
 410                                 return return_inference;
 411                         }
 412                 }
 413
 414                 #endregion
 415
 416                 protected override BlockContext CreateBlockContext (ResolveContext rc)
 417                 {
 418                         var ctx = base.CreateBlockContext (rc);
 419                         var lambda = rc.CurrentAnonymousMethod as LambdaMethod;
 420                         if (lambda != null)
 421                                 return_inference = lambda.ReturnTypeInference;
 422
 423                         ctx.StartFlowBranching (this, rc.CurrentBranching);
 424                         return ctx;
 425                 }
 426
 427                 public override Expression CreateExpressionTree (ResolveContext ec)
 428                 {
 429                         return base.CreateExpressionTree (ec);
 430                 }
 431
 432                 public override void Emit (EmitContext ec)
 433                 {
 434                         throw new NotImplementedException ();
 435                 }
 436
 437                 protected override void EmitMoveNextEpilogue (EmitContext ec)
 438                 {
 439                         var storey = (AsyncTaskStorey) Storey;
 440                         storey.EmitSetResult (ec);
 441                 }
 442
 443                 public override void EmitStatement (EmitContext ec)
 444                 {
 445                         var storey = (AsyncTaskStorey) Storey;
 446                         storey.EmitInitializer (ec);
 447                         ec.Emit (OpCodes.Ret);
 448                 }
 449         }
 450
 451         class AsyncTaskStorey : StateMachine
 452         {
 453                 int awaiters;
 454                 Field builder;
 455                 readonly TypeSpec return_type;
 456                 MethodSpec set_result;
 457                 MethodSpec set_exception;
 458                 MethodSpec builder_factory;
 459                 MethodSpec builder_start;
 460                 PropertySpec task;
 461                 LocalVariable hoisted_return;
 462                 int locals_captured;
 463                 Dictionary<TypeSpec, List<Field>> stack_fields;
 464                 Dictionary<TypeSpec, List<Field>> awaiter_fields;
 465
 466                 public AsyncTaskStorey (ParametersBlock block, IMemberContext context, AsyncInitializer initializer, TypeSpec type)
 467                         : base (block, initializer.Host, context.CurrentMemberDefinition as MemberBase, context.CurrentTypeParameters, "async", MemberKind.Class)
 468                 {
 469                         return_type = type;
 470                         awaiter_fields = new Dictionary<TypeSpec, List<Field>> ();
 471                 }
 472
 473                 #region Properties
 474
 475                 public LocalVariable HoistedReturn {
 476                         get {
 477                                 return hoisted_return;
 478                         }
 479                 }
 480
 481                 public TypeSpec ReturnType {
 482                         get {
 483                                 return return_type;
 484                         }
 485                 }
 486
 487                 public PropertySpec Task {
 488                         get {
 489                                 return task;
 490                         }
 491                 }
 492
 493                 #endregion
 494
 495                 public Field AddAwaiter (TypeSpec type, Location loc)
 496                 {
 497                         if (mutator != null)
 498                                 type = mutator.Mutate (type);
 499
 500                         List<Field> existing_fields = null;
 501                         if (awaiter_fields.TryGetValue (type, out existing_fields)) {
 502                                 foreach (var f in existing_fields) {
 503                                         if (f.IsAvailableForReuse) {
 504                                                 f.IsAvailableForReuse = false;
 505                                                 return f;
 506                                         }
 507                                 }
 508                         }
 509
 510                         var field = AddCompilerGeneratedField ("$awaiter" + awaiters++.ToString ("X"), new TypeExpression (type, Location), true);
 511                         field.Define ();
 512
 513                         if (existing_fields == null) {
 514                                 existing_fields = new List<Field> ();
 515                                 awaiter_fields.Add (type, existing_fields);
 516                         }
 517
 518                         existing_fields.Add (field);
 519                         return field;
 520                 }
 521
 522                 public Field AddCapturedLocalVariable (TypeSpec type)
 523                 {
 524                         if (mutator != null)
 525                                 type = mutator.Mutate (type);
 526
 527                         List<Field> existing_fields = null;
 528                         if (stack_fields == null) {
 529                                 stack_fields = new Dictionary<TypeSpec, List<Field>> ();
 530                         } else if (stack_fields.TryGetValue (type, out existing_fields)) {
 531                                 foreach (var f in existing_fields) {
 532                                         if (f.IsAvailableForReuse) {
 533                                                 f.IsAvailableForReuse = false;
 534                                                 return f;
 535                                         }
 536                                 }
 537                         }
 538
 539                         var field = AddCompilerGeneratedField ("$stack" + locals_captured++.ToString ("X"), new TypeExpression (type, Location), true);
 540                         field.Define ();
 541
 542                         if (existing_fields == null) {
 543                                 existing_fields = new List<Field> ();
 544                                 stack_fields.Add (type, existing_fields);
 545                         }
 546
 547                         existing_fields.Add (field);
 548
 549                         return field;
 550                 }
 551
 552                 protected override bool DoDefineMembers ()
 553                 {
 554                         PredefinedType builder_type;
 555                         PredefinedMember<MethodSpec> bf;
 556                         PredefinedMember<MethodSpec> bs;
 557                         PredefinedMember<MethodSpec> sr;
 558                         PredefinedMember<MethodSpec> se;
 559                         PredefinedMember<MethodSpec> sm;
 560                         bool has_task_return_type = false;
 561                         var pred_members = Module.PredefinedMembers;
 562
 563                         if (return_type.Kind == MemberKind.Void) {
 564                                 builder_type = Module.PredefinedTypes.AsyncVoidMethodBuilder;
 565                                 bf = pred_members.AsyncVoidMethodBuilderCreate;
 566                                 bs = pred_members.AsyncVoidMethodBuilderStart;
 567                                 sr = pred_members.AsyncVoidMethodBuilderSetResult;
 568                                 se = pred_members.AsyncVoidMethodBuilderSetException;
 569                                 sm = pred_members.AsyncVoidMethodBuilderSetStateMachine;
 570                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 571                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilder;
 572                                 bf = pred_members.AsyncTaskMethodBuilderCreate;
 573                                 bs = pred_members.AsyncTaskMethodBuilderStart;
 574                                 sr = pred_members.AsyncTaskMethodBuilderSetResult;
 575                                 se = pred_members.AsyncTaskMethodBuilderSetException;
 576                                 sm = pred_members.AsyncTaskMethodBuilderSetStateMachine;
 577                                 task = pred_members.AsyncTaskMethodBuilderTask.Get ();
 578                         } else {
 579                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilderGeneric;
 580                                 bf = pred_members.AsyncTaskMethodBuilderGenericCreate;
 581                                 bs = pred_members.AsyncTaskMethodBuilderGenericStart;
 582                                 sr = pred_members.AsyncTaskMethodBuilderGenericSetResult;
 583                                 se = pred_members.AsyncTaskMethodBuilderGenericSetException;
 584                                 sm = pred_members.AsyncTaskMethodBuilderGenericSetStateMachine;
 585                                 task = pred_members.AsyncTaskMethodBuilderGenericTask.Get ();
 586                                 has_task_return_type = true;
 587                         }
 588
 589                         set_result = sr.Get ();
 590                         set_exception = se.Get ();
 591                         builder_factory = bf.Get ();
 592                         builder_start = bs.Get ();
 593
 594                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 595                         var set_statemachine = sm.Get ();
 596
 597                         if (!builder_type.Define () || !istate_machine.Define () || set_result == null || builder_factory == null ||
 598                                 set_exception == null || set_statemachine == null || builder_start == null ||
 599                                 !Module.PredefinedTypes.INotifyCompletion.Define ()) {
 600                                 Report.Error (1993, Location,
 601                                         "Cannot find compiler required types for asynchronous functions support. Are you targeting the wrong framework version?");
 602                                 return base.DoDefineMembers ();
 603                         }
 604
 605                         var bt = builder_type.TypeSpec;
 606
 607                         //
 608                         // Inflate generic Task types
 609                         //
 610                         if (has_task_return_type) {
 611                                 var task_return_type = return_type.TypeArguments;
 612                                 if (mutator != null)
 613                                         task_return_type = mutator.Mutate (task_return_type);
 614
 615                                 bt = bt.MakeGenericType (Module, task_return_type);
 616                                 set_result = MemberCache.GetMember (bt, set_result);
 617                                 set_exception = MemberCache.GetMember (bt, set_exception);
 618                                 set_statemachine = MemberCache.GetMember (bt, set_statemachine);
 619
 620                                 if (task != null)
 621                                         task = MemberCache.GetMember (bt, task);
 622                         }
 623
 624                         builder = AddCompilerGeneratedField ("$builder", new TypeExpression (bt, Location));
 625
 626                         var set_state_machine = new Method (this, new TypeExpression (Compiler.BuiltinTypes.Void, Location),
 627                                 Modifiers.COMPILER_GENERATED | Modifiers.DEBUGGER_HIDDEN | Modifiers.PUBLIC,
 628                                 new MemberName ("SetStateMachine"),
 629                                 ParametersCompiled.CreateFullyResolved (
 630                                         new Parameter (new TypeExpression (istate_machine.TypeSpec, Location), "stateMachine", Parameter.Modifier.NONE, null, Location),
 631                                         istate_machine.TypeSpec),
 632                                 null);
 633
 634                         ToplevelBlock block = new ToplevelBlock (Compiler, set_state_machine.ParameterInfo, Location);
 635                         block.IsCompilerGenerated = true;
 636                         set_state_machine.Block = block;
 637
 638                         Members.Add (set_state_machine);
 639
 640                         if (!base.DoDefineMembers ())
 641                                 return false;
 642
 643                         //
 644                         // Fabricates SetStateMachine method
 645                         //
 646                         // public void SetStateMachine (IAsyncStateMachine stateMachine)
 647                         // {
 648                         //    $builder.SetStateMachine (stateMachine);
 649                         // }
 650                         //
 651                         var mg = MethodGroupExpr.CreatePredefined (set_statemachine, bt, Location);
 652                         mg.InstanceExpression = new FieldExpr (builder, Location);
 653
 654                         var param_reference = block.GetParameterReference (0, Location);
 655                         param_reference.Type = istate_machine.TypeSpec;
 656                         param_reference.eclass = ExprClass.Variable;
 657
 658                         var args = new Arguments (1);
 659                         args.Add (new Argument (param_reference));
 660                         set_state_machine.Block.AddStatement (new StatementExpression (new Invocation (mg, args)));
 661
 662                         if (has_task_return_type) {
 663                                 hoisted_return = LocalVariable.CreateCompilerGenerated (bt.TypeArguments[0], StateMachineMethod.Block, Location);
 664                         }
 665
 666                         return true;
 667                 }
 668
 669                 public void EmitAwaitOnCompletedDynamic (EmitContext ec, FieldExpr awaiter)
 670                 {
 671                         var critical = Module.PredefinedTypes.ICriticalNotifyCompletion;
 672                         if (!critical.Define ()) {
 673                                 throw new NotImplementedException ();
 674                         }
 675
 676                         var temp_critical = new LocalTemporary (critical.TypeSpec);
 677                         var label_critical = ec.DefineLabel ();
 678                         var label_end = ec.DefineLabel ();
 679
 680                         //
 681                         // Special path for dynamic awaiters
 682                         //
 683                         // var awaiter = this.$awaiter as ICriticalNotifyCompletion;
 684                         // if (awaiter == null) {
 685                         //    var completion = (INotifyCompletion) this.$awaiter;
 686                         //    this.$builder.AwaitOnCompleted (ref completion, ref this);
 687                         // } else {
 688                         //    this.$builder.AwaitUnsafeOnCompleted (ref awaiter, ref this);
 689                         // }
 690                         //
 691                         awaiter.Emit (ec);
 692                         ec.Emit (OpCodes.Isinst, critical.TypeSpec);
 693                         temp_critical.Store (ec);
 694                         temp_critical.Emit (ec);
 695                         ec.Emit (OpCodes.Brtrue_S, label_critical);
 696
 697                         var temp = new LocalTemporary (Module.PredefinedTypes.INotifyCompletion.TypeSpec);
 698                         awaiter.Emit (ec);
 699                         ec.Emit (OpCodes.Castclass, temp.Type);
 700                         temp.Store (ec);
 701                         EmitOnCompleted (ec, temp, false);
 702                         temp.Release (ec);
 703                         ec.Emit (OpCodes.Br_S, label_end);
 704
 705                         ec.MarkLabel (label_critical);
 706
 707                         EmitOnCompleted (ec, temp_critical, true);
 708
 709                         ec.MarkLabel (label_end);
 710
 711                         temp_critical.Release (ec);
 712                 }
 713
 714                 public void EmitAwaitOnCompleted (EmitContext ec, FieldExpr awaiter)
 715                 {
 716                         bool unsafe_version = false;
 717                         if (Module.PredefinedTypes.ICriticalNotifyCompletion.Define ()) {
 718                                 unsafe_version = awaiter.Type.ImplementsInterface (Module.PredefinedTypes.ICriticalNotifyCompletion.TypeSpec, false);
 719                         }
 720
 721                         EmitOnCompleted (ec, awaiter, unsafe_version);
 722                 }
 723
 724                 void EmitOnCompleted (EmitContext ec, Expression awaiter, bool unsafeVersion)
 725                 {
 726                         var pm = Module.PredefinedMembers;
 727                         PredefinedMember<MethodSpec> predefined;
 728                         bool has_task_return_type = false;
 729                         if (return_type.Kind == MemberKind.Void) {
 730                                 predefined = unsafeVersion ? pm.AsyncVoidMethodBuilderOnCompletedUnsafe : pm.AsyncVoidMethodBuilderOnCompleted;
 731                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 732                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderOnCompletedUnsafe : pm.AsyncTaskMethodBuilderOnCompleted;
 733                         } else {
 734                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderGenericOnCompletedUnsafe : pm.AsyncTaskMethodBuilderGenericOnCompleted;
 735                                 has_task_return_type = true;
 736                         }
 737
 738                         var on_completed = predefined.Resolve (Location);
 739                         if (on_completed == null)
 740                                 return;
 741
 742                         if (has_task_return_type)
 743                                 on_completed = MemberCache.GetMember<MethodSpec> (set_result.DeclaringType, on_completed);
 744
 745                         on_completed = on_completed.MakeGenericMethod (this, awaiter.Type, ec.CurrentType);
 746
 747                         var mg = MethodGroupExpr.CreatePredefined (on_completed, on_completed.DeclaringType, Location);
 748                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 749                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 750                         };
 751
 752                         // TODO: CompilerGeneratedThis is enough for structs
 753                         var temp_this = new LocalTemporary (CurrentType);
 754                         temp_this.EmitAssign (ec, new CompilerGeneratedThis (CurrentType, Location), false, false);
 755
 756                         var args = new Arguments (2);
 757                         args.Add (new Argument (awaiter, Argument.AType.Ref));
 758                         args.Add (new Argument (temp_this, Argument.AType.Ref));
 759                         mg.EmitCall (ec, args);
 760
 761                         temp_this.Release (ec);
 762                 }
 763
 764                 public void EmitInitializer (EmitContext ec)
 765                 {
 766                         //
 767                         // Some predefined types are missing
 768                         //
 769                         if (builder == null)
 770                                 return;
 771
 772                         var instance = (TemporaryVariableReference) Instance;
 773                         var builder_field = builder.Spec;
 774                         if (MemberName.Arity > 0) {
 775                                 builder_field = MemberCache.GetMember (instance.Type, builder_field);
 776                         }
 777
 778                         //
 779                         // Inflated factory method when task is of generic type
 780                         //
 781                         if (builder_factory.DeclaringType.IsGeneric) {
 782                                 var task_return_type = return_type.TypeArguments;
 783                                 var bt = builder_factory.DeclaringType.MakeGenericType (Module, task_return_type);
 784                                 builder_factory = MemberCache.GetMember (bt, builder_factory);
 785                                 builder_start = MemberCache.GetMember (bt, builder_start);
 786                         }
 787
 788                         //
 789                         // stateMachine.$builder = AsyncTaskMethodBuilder<{task-type}>.Create();
 790                         //
 791                         instance.Emit (ec); // .AddressOf (ec, AddressOp.Store);
 792                         ec.Emit (OpCodes.Call, builder_factory);
 793                         ec.Emit (OpCodes.Stfld, builder_field);
 794
 795                         //
 796                         // stateMachine.$builder.Start<{storey-type}>(ref stateMachine);
 797                         //
 798                         instance.Emit (ec); //.AddressOf (ec, AddressOp.Store);
 799                         ec.Emit (OpCodes.Ldflda, builder_field);
 800                         if (Task != null)
 801                                 ec.Emit (OpCodes.Dup);
 802                         instance.AddressOf (ec, AddressOp.Store);
 803                         ec.Emit (OpCodes.Call, builder_start.MakeGenericMethod (Module, instance.Type));
 804
 805                         //
 806                         // Emits return stateMachine.$builder.Task;
 807                         //
 808                         if (Task != null) {
 809                                 var task_get = Task.Get;
 810
 811                                 if (MemberName.Arity > 0) {
 812                                         task_get = MemberCache.GetMember (builder_field.MemberType, task_get);
 813                                 }
 814
 815                                 var pe_task = new PropertyExpr (Task, Location) {
 816                                         InstanceExpression = EmptyExpression.Null,      // Comes from the dup above
 817                                         Getter = task_get
 818                                 };
 819
 820                                 pe_task.Emit (ec);
 821                         }
 822                 }
 823
 824                 public void EmitSetException (EmitContext ec, LocalVariableReference exceptionVariable)
 825                 {
 826                         //
 827                         // $builder.SetException (Exception)
 828                         //
 829                         var mg = MethodGroupExpr.CreatePredefined (set_exception, set_exception.DeclaringType, Location);
 830                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 831                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 832                         };
 833
 834                         Arguments args = new Arguments (1);
 835                         args.Add (new Argument (exceptionVariable));
 836
 837                         mg.EmitCall (ec, args);
 838                 }
 839
 840                 public void EmitSetResult (EmitContext ec)
 841                 {
 842                         //
 843                         // $builder.SetResult ();
 844                         // $builder.SetResult<return-type> (value);
 845                         //
 846                         var mg = MethodGroupExpr.CreatePredefined (set_result, set_result.DeclaringType, Location);
 847                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 848                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 849                         };
 850
 851                         Arguments args;
 852                         if (hoisted_return == null) {
 853                                 args = new Arguments (0);
 854                         } else {
 855                                 args = new Arguments (1);
 856                                 args.Add (new Argument (new LocalVariableReference (hoisted_return, Location)));
 857                         }
 858
 859                         mg.EmitCall (ec, args);
 860                 }
 861
 862                 protected override TypeSpec[] ResolveBaseTypes (out FullNamedExpression base_class)
 863                 {
 864                         base_type = Compiler.BuiltinTypes.Object; // ValueType;
 865                         base_class = null;
 866
 867                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 868                         if (istate_machine.Define ()) {
 869                                 return new[] { istate_machine.TypeSpec };
 870                         }
 871
 872                         return null;
 873                 }
 874         }
 875
 876         class StackFieldExpr : FieldExpr, IExpressionCleanup
 877         {
 878                 public StackFieldExpr (Field field)
 879                         : base (field, Location.Null)
 880                 {
 881                 }
 882
 883                 public override void AddressOf (EmitContext ec, AddressOp mode)
 884                 {
 885                         base.AddressOf (ec, mode);
 886
 887                         if (mode == AddressOp.Load) {
 888                                 var field = (Field) spec.MemberDefinition;
 889                                 field.IsAvailableForReuse = true;
 890                         }
 891                 }
 892
 893                 public override void Emit (EmitContext ec)
 894                 {
 895                         base.Emit (ec);
 896
 897                         var field = (Field) spec.MemberDefinition;
 898                         field.IsAvailableForReuse = true;
 899
 900                         //
 901                         // Release any captured reference type stack variables
 902                         // to imitate real stack behavour and help GC stuff early
 903                         //
 904                         if (TypeSpec.IsReferenceType (type)) {
 905                                 ec.AddStatementEpilog (this);
 906                         }
 907                 }
 908
 909                 void IExpressionCleanup.EmitCleanup (EmitContext ec)
 910                 {
 911                         EmitAssign (ec, new NullConstant (type, loc), false, false);
 912                 }
 913         }
 914 }