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                 public override void FlowAnalysis (FlowAnalysisContext fc)
  69                 {
  70                         stmt.Expr.FlowAnalysis (fc);
  71
  72                         stmt.RegisterResumePoint ();
  73                 }
  74
  75                 protected override Expression DoResolve (ResolveContext rc)
  76                 {
  77                         if (rc.HasSet (ResolveContext.Options.LockScope)) {
  78                                 rc.Report.Error (1996, loc,
  79                                         "The `await' operator cannot be used in the body of a lock statement");
  80                         }
  81
  82                         if (rc.IsUnsafe) {
  83                                 rc.Report.Error (4004, loc,
  84                                         "The `await' operator cannot be used in an unsafe context");
  85                         }
  86
  87                         var bc = (BlockContext) rc;
  88
  89                         stmt = new AwaitStatement (expr, loc);
  90                         if (!stmt.Resolve (bc))
  91                                 return null;
  92
  93                         type = stmt.ResultType;
  94                         eclass = ExprClass.Variable;
  95                         return this;
  96                 }
  97
  98                 public override void Emit (EmitContext ec)
  99                 {
 100                         stmt.EmitPrologue (ec);
 101
 102                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 103                                 stmt.Emit (ec);
 104                         }
 105                 }
 106
 107                 public override Expression EmitToField (EmitContext ec)
 108                 {
 109                         stmt.EmitPrologue (ec);
 110                         return stmt.GetResultExpression (ec);
 111                 }
 112
 113                 public void EmitAssign (EmitContext ec, FieldExpr field)
 114                 {
 115                         stmt.EmitPrologue (ec);
 116                         field.InstanceExpression.Emit (ec);
 117                         stmt.Emit (ec);
 118                 }
 119
 120                 public override void EmitStatement (EmitContext ec)
 121                 {
 122                         stmt.EmitStatement (ec);
 123                 }
 124
 125                 public override void MarkReachable (Reachability rc)
 126                 {
 127                         base.MarkReachable (rc);
 128                         stmt.MarkReachable (rc);
 129                 }
 130
 131                 public override object Accept (StructuralVisitor visitor)
 132                 {
 133                         return visitor.Visit (this);
 134                 }
 135         }
 136
 137         public class AwaitStatement : YieldStatement<AsyncInitializer>
 138         {
 139                 public sealed class AwaitableMemberAccess : MemberAccess
 140                 {
 141                         public AwaitableMemberAccess (Expression expr)
 142                                 : base (expr, "GetAwaiter")
 143                         {
 144                         }
 145
 146                         public bool ProbingMode { get; set; }
 147
 148                         protected override void Error_TypeDoesNotContainDefinition (ResolveContext rc, TypeSpec type, string name)
 149                         {
 150                                 Error_OperatorCannotBeApplied (rc, type);
 151                         }
 152
 153                         protected override void Error_OperatorCannotBeApplied (ResolveContext rc, TypeSpec type)
 154                         {
 155                                 if (ProbingMode)
 156                                         return;
 157
 158                                 var invocation = LeftExpression as Invocation;
 159                                 if (invocation != null && invocation.MethodGroup != null && (invocation.MethodGroup.BestCandidate.Modifiers & Modifiers.ASYNC) != 0) {
 160                                         rc.Report.Error (4008, loc, "Cannot await void method `{0}'. Consider changing method return type to `Task'",
 161                                                 invocation.GetSignatureForError ());
 162                                 } else {
 163                                         rc.Report.Error (4001, loc, "Cannot await `{0}' expression", type.GetSignatureForError ());
 164                                 }
 165                         }
 166                 }
 167
 168                 sealed class GetResultInvocation : Invocation
 169                 {
 170                         public GetResultInvocation (MethodGroupExpr mge, Arguments arguments)
 171                                 : base (null, arguments)
 172                         {
 173                                 mg = mge;
 174                                 type = mg.BestCandidateReturnType;
 175                         }
 176
 177                         public override Expression EmitToField (EmitContext ec)
 178                         {
 179                                 return this;
 180                         }
 181                 }
 182
 183                 Field awaiter;
 184                 AwaiterDefinition awaiter_definition;
 185                 TypeSpec type;
 186                 TypeSpec result_type;
 187
 188                 public AwaitStatement (Expression expr, Location loc)
 189                         : base (expr, loc)
 190                 {
 191                         unwind_protect = true;
 192                 }
 193
 194                 #region Properties
 195
 196                 bool IsDynamic {
 197                         get {
 198                                 return awaiter_definition == null;
 199                         }
 200                 }
 201
 202                 public TypeSpec ResultType {
 203                         get {
 204                                 return result_type;
 205                         }
 206                 }
 207
 208                 #endregion
 209
 210                 protected override void DoEmit (EmitContext ec)
 211                 {
 212                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 213                                 GetResultExpression (ec).Emit (ec);
 214                         }
 215                 }
 216
 217                 public Expression GetResultExpression (EmitContext ec)
 218                 {
 219                         var fe_awaiter = new FieldExpr (awaiter, loc);
 220                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 221
 222                         //
 223                         // result = awaiter.GetResult ();
 224                         //
 225                         if (IsDynamic) {
 226                                 var rc = new ResolveContext (ec.MemberContext);
 227                                 return new Invocation (new MemberAccess (fe_awaiter, "GetResult"), new Arguments (0)).Resolve (rc);
 228                         }
 229
 230                         var mg_result = MethodGroupExpr.CreatePredefined (awaiter_definition.GetResult, fe_awaiter.Type, loc);
 231                         mg_result.InstanceExpression = fe_awaiter;
 232
 233                         return new GetResultInvocation (mg_result, new Arguments (0));
 234                 }
 235
 236                 public void EmitPrologue (EmitContext ec)
 237                 {
 238                         awaiter = ((AsyncTaskStorey) machine_initializer.Storey).AddAwaiter (expr.Type);
 239
 240                         var fe_awaiter = new FieldExpr (awaiter, loc);
 241                         fe_awaiter.InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, loc);
 242
 243                         Label skip_continuation = ec.DefineLabel ();
 244
 245                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 246                                 //
 247                                 // awaiter = expr.GetAwaiter ();
 248                                 //
 249                                 fe_awaiter.EmitAssign (ec, expr, false, false);
 250
 251                                 Expression completed_expr;
 252                                 if (IsDynamic) {
 253                                         var rc = new ResolveContext (ec.MemberContext);
 254
 255                                         Arguments dargs = new Arguments (1);
 256                                         dargs.Add (new Argument (fe_awaiter));
 257                                         completed_expr = new DynamicMemberBinder ("IsCompleted", dargs, loc).Resolve (rc);
 258
 259                                         dargs = new Arguments (1);
 260                                         dargs.Add (new Argument (completed_expr));
 261                                         completed_expr = new DynamicConversion (ec.Module.Compiler.BuiltinTypes.Bool, 0, dargs, loc).Resolve (rc);
 262                                 } else {
 263                                         var pe = PropertyExpr.CreatePredefined (awaiter_definition.IsCompleted, loc);
 264                                         pe.InstanceExpression = fe_awaiter;
 265                                         completed_expr = pe;
 266                                 }
 267
 268                                 completed_expr.EmitBranchable (ec, skip_continuation, true);
 269                         }
 270
 271                         base.DoEmit (ec);
 272
 273                         //
 274                         // The stack has to be empty before calling await continuation. We handle this
 275                         // by lifting values which would be left on stack into class fields. The process
 276                         // is quite complicated and quite hard to test because any expression can possibly
 277                         // leave a value on the stack.
 278                         //
 279                         // Following assert fails when some of expression called before is missing EmitToField
 280                         // or parent expression fails to find await in children expressions
 281                         //
 282                         ec.AssertEmptyStack ();
 283
 284                         var storey = (AsyncTaskStorey) machine_initializer.Storey;
 285                         if (IsDynamic) {
 286                                 storey.EmitAwaitOnCompletedDynamic (ec, fe_awaiter);
 287                         } else {
 288                                 storey.EmitAwaitOnCompleted (ec, fe_awaiter);
 289                         }
 290
 291                         // Return ok
 292                         machine_initializer.EmitLeave (ec, unwind_protect);
 293
 294                         ec.MarkLabel (resume_point);
 295                         ec.MarkLabel (skip_continuation);
 296                 }
 297
 298                 public void EmitStatement (EmitContext ec)
 299                 {
 300                         EmitPrologue (ec);
 301                         DoEmit (ec);
 302
 303                         awaiter.IsAvailableForReuse = true;
 304
 305                         if (ResultType.Kind != MemberKind.Void)
 306                                 ec.Emit (OpCodes.Pop);
 307                 }
 308
 309                 void Error_WrongAwaiterPattern (ResolveContext rc, TypeSpec awaiter)
 310                 {
 311                         rc.Report.Error (4011, loc, "The awaiter type `{0}' must have suitable IsCompleted and GetResult members",
 312                                 awaiter.GetSignatureForError ());
 313                 }
 314
 315                 public override bool Resolve (BlockContext bc)
 316                 {
 317                         if (bc.CurrentBlock is Linq.QueryBlock) {
 318                                 bc.Report.Error (1995, loc,
 319                                         "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");
 320                                 return false;
 321                         }
 322
 323                         if (!base.Resolve (bc))
 324                                 return false;
 325
 326                         type = expr.Type;
 327                         Arguments args = new Arguments (0);
 328
 329                         //
 330                         // The await expression is of dynamic type
 331                         //
 332                         if (type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 333                                 result_type = type;
 334                                 expr = new Invocation (new MemberAccess (expr, "GetAwaiter"), args).Resolve (bc);
 335                                 return true;
 336                         }
 337
 338                         //
 339                         // Check whether the expression is awaitable
 340                         //
 341                         Expression ama = new AwaitableMemberAccess (expr).Resolve (bc);
 342                         if (ama == null)
 343                                 return false;
 344
 345                         var errors_printer = new SessionReportPrinter ();
 346                         var old = bc.Report.SetPrinter (errors_printer);
 347                         ama = new Invocation (ama, args).Resolve (bc);
 348                         bc.Report.SetPrinter (old);
 349
 350                         if (errors_printer.ErrorsCount > 0 || !MemberAccess.IsValidDotExpression (ama.Type)) {
 351                                 bc.Report.Error (1986, expr.Location,
 352                                         "The `await' operand type `{0}' must have suitable GetAwaiter method",
 353                                         expr.Type.GetSignatureForError ());
 354
 355                                 return false;
 356                         }
 357
 358                         var awaiter_type = ama.Type;
 359
 360                         awaiter_definition = bc.Module.GetAwaiter (awaiter_type);
 361
 362                         if (!awaiter_definition.IsValidPattern) {
 363                                 Error_WrongAwaiterPattern (bc, awaiter_type);
 364                                 return false;
 365                         }
 366
 367                         if (!awaiter_definition.INotifyCompletion) {
 368                                 bc.Report.Error (4027, loc, "The awaiter type `{0}' must implement interface `{1}'",
 369                                         awaiter_type.GetSignatureForError (), bc.Module.PredefinedTypes.INotifyCompletion.GetSignatureForError ());
 370                                 return false;
 371                         }
 372
 373                         expr = ama;
 374                         result_type = awaiter_definition.GetResult.ReturnType;
 375
 376                         return true;
 377                 }
 378         }
 379
 380         class AsyncInitializerStatement : StatementExpression
 381         {
 382                 public AsyncInitializerStatement (AsyncInitializer expr)
 383                         : base (expr)
 384                 {
 385                 }
 386
 387                 protected override bool DoFlowAnalysis (FlowAnalysisContext fc)
 388                 {
 389                         base.DoFlowAnalysis (fc);
 390
 391                         var init = (AsyncInitializer) Expr;
 392                         var res = !init.Block.HasReachableClosingBrace;
 393                         var storey = (AsyncTaskStorey) init.Storey;
 394
 395                         if (storey.ReturnType.IsGenericTask)
 396                                 return res;
 397
 398                         return true;
 399                 }
 400
 401                 public override Reachability MarkReachable (Reachability rc)
 402                 {
 403                         if (!rc.IsUnreachable)
 404                                 reachable = true;
 405
 406                         var init = (AsyncInitializer) Expr;
 407                         rc = init.Block.MarkReachable (rc);
 408
 409                         var storey = (AsyncTaskStorey) init.Storey;
 410
 411                         //
 412                         // Explicit return is required for Task<T> state machine
 413                         //
 414                         if (storey.ReturnType != null && storey.ReturnType.IsGenericTask)
 415                                 return rc;
 416
 417                     return Reachability.CreateUnreachable ();
 418                 }
 419         }
 420
 421         public class AsyncInitializer : StateMachineInitializer
 422         {
 423                 TypeInferenceContext return_inference;
 424
 425                 public AsyncInitializer (ParametersBlock block, TypeDefinition host, TypeSpec returnType)
 426                         : base (block, host, returnType)
 427                 {
 428                 }
 429
 430                 #region Properties
 431
 432                 public override string ContainerType {
 433                         get {
 434                                 return "async state machine block";
 435                         }
 436                 }
 437
 438                 public TypeSpec DelegateType {
 439                         get; set;
 440                 }
 441
 442                 public StackFieldExpr HoistedReturnState {
 443                         get; set;
 444                 }
 445
 446                 public override bool IsIterator {
 447                         get {
 448                                 return false;
 449                         }
 450                 }
 451
 452                 public TypeInferenceContext ReturnTypeInference {
 453                         get {
 454                                 return return_inference;
 455                         }
 456                 }
 457
 458                 #endregion
 459
 460                 protected override BlockContext CreateBlockContext (BlockContext bc)
 461                 {
 462                         var ctx = base.CreateBlockContext (bc);
 463                         var am = bc.CurrentAnonymousMethod as AnonymousMethodBody;
 464                         if (am != null)
 465                                 return_inference = am.ReturnTypeInference;
 466
 467                         ctx.Set (ResolveContext.Options.TryScope);
 468
 469                         return ctx;
 470                 }
 471
 472                 public override void Emit (EmitContext ec)
 473                 {
 474                         throw new NotImplementedException ();
 475                 }
 476
 477                 protected override void EmitMoveNextEpilogue (EmitContext ec)
 478                 {
 479                         var storey = (AsyncTaskStorey) Storey;
 480                         storey.EmitSetResult (ec);
 481                 }
 482
 483                 public override void EmitStatement (EmitContext ec)
 484                 {
 485                         var storey = (AsyncTaskStorey) Storey;
 486                         storey.EmitInitializer (ec);
 487                         ec.Emit (OpCodes.Ret);
 488                 }
 489
 490                 public override void MarkReachable (Reachability rc)
 491                 {
 492                         //
 493                         // Reachability has been done in AsyncInitializerStatement
 494                         //
 495                 }
 496         }
 497
 498         class AsyncTaskStorey : StateMachine
 499         {
 500                 int awaiters;
 501                 Field builder;
 502                 readonly TypeSpec return_type;
 503                 MethodSpec set_result;
 504                 MethodSpec set_exception;
 505                 MethodSpec builder_factory;
 506                 MethodSpec builder_start;
 507                 PropertySpec task;
 508                 int locals_captured;
 509                 Dictionary<TypeSpec, List<Field>> stack_fields;
 510                 Dictionary<TypeSpec, List<Field>> awaiter_fields;
 511
 512                 public AsyncTaskStorey (ParametersBlock block, IMemberContext context, AsyncInitializer initializer, TypeSpec type)
 513                         : base (block, initializer.Host, context.CurrentMemberDefinition as MemberBase, context.CurrentTypeParameters, "async", MemberKind.Struct)
 514                 {
 515                         return_type = type;
 516                         awaiter_fields = new Dictionary<TypeSpec, List<Field>> ();
 517                 }
 518
 519                 #region Properties
 520
 521                 public Expression HoistedReturnValue { get; set; }
 522
 523                 public TypeSpec ReturnType {
 524                         get {
 525                                 return return_type;
 526                         }
 527                 }
 528
 529                 public PropertySpec Task {
 530                         get {
 531                                 return task;
 532                         }
 533                 }
 534
 535                 protected override TypeAttributes TypeAttr {
 536                         get {
 537                                 return base.TypeAttr & ~TypeAttributes.SequentialLayout;
 538                         }
 539                 }
 540
 541                 #endregion
 542
 543                 public Field AddAwaiter (TypeSpec type)
 544                 {
 545                         if (mutator != null)
 546                                 type = mutator.Mutate (type);
 547
 548                         List<Field> existing_fields;
 549                         if (awaiter_fields.TryGetValue (type, out existing_fields)) {
 550                                 foreach (var f in existing_fields) {
 551                                         if (f.IsAvailableForReuse) {
 552                                                 f.IsAvailableForReuse = false;
 553                                                 return f;
 554                                         }
 555                                 }
 556                         }
 557
 558                         var field = AddCompilerGeneratedField ("$awaiter" + awaiters++.ToString ("X"), new TypeExpression (type, Location), true);
 559                         field.Define ();
 560
 561                         if (existing_fields == null) {
 562                                 existing_fields = new List<Field> ();
 563                                 awaiter_fields.Add (type, existing_fields);
 564                         }
 565
 566                         existing_fields.Add (field);
 567                         return field;
 568                 }
 569
 570                 public Field AddCapturedLocalVariable (TypeSpec type, bool requiresUninitialized = false)
 571                 {
 572                         if (mutator != null)
 573                                 type = mutator.Mutate (type);
 574
 575                         List<Field> existing_fields = null;
 576                         if (stack_fields == null) {
 577                                 stack_fields = new Dictionary<TypeSpec, List<Field>> ();
 578                         } else if (stack_fields.TryGetValue (type, out existing_fields) && !requiresUninitialized) {
 579                                 foreach (var f in existing_fields) {
 580                                         if (f.IsAvailableForReuse) {
 581                                                 f.IsAvailableForReuse = false;
 582                                                 return f;
 583                                         }
 584                                 }
 585                         }
 586
 587                         var field = AddCompilerGeneratedField ("$stack" + locals_captured++.ToString ("X"), new TypeExpression (type, Location), true);
 588                         field.Define ();
 589
 590                         if (existing_fields == null) {
 591                                 existing_fields = new List<Field> ();
 592                                 stack_fields.Add (type, existing_fields);
 593                         }
 594
 595                         existing_fields.Add (field);
 596
 597                         return field;
 598                 }
 599
 600                 protected override bool DoDefineMembers ()
 601                 {
 602                         PredefinedType builder_type;
 603                         PredefinedMember<MethodSpec> bf;
 604                         PredefinedMember<MethodSpec> bs;
 605                         PredefinedMember<MethodSpec> sr;
 606                         PredefinedMember<MethodSpec> se;
 607                         PredefinedMember<MethodSpec> sm;
 608                         bool has_task_return_type = false;
 609                         var pred_members = Module.PredefinedMembers;
 610
 611                         if (return_type.Kind == MemberKind.Void) {
 612                                 builder_type = Module.PredefinedTypes.AsyncVoidMethodBuilder;
 613                                 bf = pred_members.AsyncVoidMethodBuilderCreate;
 614                                 bs = pred_members.AsyncVoidMethodBuilderStart;
 615                                 sr = pred_members.AsyncVoidMethodBuilderSetResult;
 616                                 se = pred_members.AsyncVoidMethodBuilderSetException;
 617                                 sm = pred_members.AsyncVoidMethodBuilderSetStateMachine;
 618                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 619                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilder;
 620                                 bf = pred_members.AsyncTaskMethodBuilderCreate;
 621                                 bs = pred_members.AsyncTaskMethodBuilderStart;
 622                                 sr = pred_members.AsyncTaskMethodBuilderSetResult;
 623                                 se = pred_members.AsyncTaskMethodBuilderSetException;
 624                                 sm = pred_members.AsyncTaskMethodBuilderSetStateMachine;
 625                                 task = pred_members.AsyncTaskMethodBuilderTask.Get ();
 626                         } else {
 627                                 builder_type = Module.PredefinedTypes.AsyncTaskMethodBuilderGeneric;
 628                                 bf = pred_members.AsyncTaskMethodBuilderGenericCreate;
 629                                 bs = pred_members.AsyncTaskMethodBuilderGenericStart;
 630                                 sr = pred_members.AsyncTaskMethodBuilderGenericSetResult;
 631                                 se = pred_members.AsyncTaskMethodBuilderGenericSetException;
 632                                 sm = pred_members.AsyncTaskMethodBuilderGenericSetStateMachine;
 633                                 task = pred_members.AsyncTaskMethodBuilderGenericTask.Get ();
 634                                 has_task_return_type = true;
 635                         }
 636
 637                         set_result = sr.Get ();
 638                         set_exception = se.Get ();
 639                         builder_factory = bf.Get ();
 640                         builder_start = bs.Get ();
 641
 642                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 643                         var set_statemachine = sm.Get ();
 644
 645                         if (!builder_type.Define () || !istate_machine.Define () || set_result == null || builder_factory == null ||
 646                                 set_exception == null || set_statemachine == null || builder_start == null ||
 647                                 !Module.PredefinedTypes.INotifyCompletion.Define ()) {
 648                                 Report.Error (1993, Location,
 649                                         "Cannot find compiler required types for asynchronous functions support. Are you targeting the wrong framework version?");
 650                                 return base.DoDefineMembers ();
 651                         }
 652
 653                         var bt = builder_type.TypeSpec;
 654
 655                         //
 656                         // Inflate generic Task types
 657                         //
 658                         if (has_task_return_type) {
 659                                 var task_return_type = return_type.TypeArguments;
 660                                 if (mutator != null)
 661                                         task_return_type = mutator.Mutate (task_return_type);
 662
 663                                 bt = bt.MakeGenericType (Module, task_return_type);
 664                                 set_result = MemberCache.GetMember (bt, set_result);
 665                                 set_exception = MemberCache.GetMember (bt, set_exception);
 666                                 set_statemachine = MemberCache.GetMember (bt, set_statemachine);
 667
 668                                 if (task != null)
 669                                         task = MemberCache.GetMember (bt, task);
 670                         }
 671
 672                         builder = AddCompilerGeneratedField ("$builder", new TypeExpression (bt, Location));
 673
 674                         var set_state_machine = new Method (this, new TypeExpression (Compiler.BuiltinTypes.Void, Location),
 675                                 Modifiers.COMPILER_GENERATED | Modifiers.DEBUGGER_HIDDEN | Modifiers.PUBLIC,
 676                                 new MemberName ("SetStateMachine"),
 677                                 ParametersCompiled.CreateFullyResolved (
 678                                         new Parameter (new TypeExpression (istate_machine.TypeSpec, Location), "stateMachine", Parameter.Modifier.NONE, null, Location),
 679                                         istate_machine.TypeSpec),
 680                                 null);
 681
 682                         ToplevelBlock block = new ToplevelBlock (Compiler, set_state_machine.ParameterInfo, Location);
 683                         block.IsCompilerGenerated = true;
 684                         set_state_machine.Block = block;
 685
 686                         Members.Add (set_state_machine);
 687
 688                         if (!base.DoDefineMembers ())
 689                                 return false;
 690
 691                         //
 692                         // Fabricates SetStateMachine method
 693                         //
 694                         // public void SetStateMachine (IAsyncStateMachine stateMachine)
 695                         // {
 696                         //    $builder.SetStateMachine (stateMachine);
 697                         // }
 698                         //
 699                         var mg = MethodGroupExpr.CreatePredefined (set_statemachine, bt, Location);
 700                         mg.InstanceExpression = new FieldExpr (builder, Location);
 701
 702                         var param_reference = block.GetParameterReference (0, Location);
 703                         param_reference.Type = istate_machine.TypeSpec;
 704                         param_reference.eclass = ExprClass.Variable;
 705
 706                         var args = new Arguments (1);
 707                         args.Add (new Argument (param_reference));
 708                         set_state_machine.Block.AddStatement (new StatementExpression (new Invocation (mg, args)));
 709
 710                         if (has_task_return_type) {
 711                                 HoistedReturnValue = TemporaryVariableReference.Create (bt.TypeArguments [0], StateMachineMethod.Block, Location);
 712                         }
 713
 714                         return true;
 715                 }
 716
 717                 public void EmitAwaitOnCompletedDynamic (EmitContext ec, FieldExpr awaiter)
 718                 {
 719                         var critical = Module.PredefinedTypes.ICriticalNotifyCompletion;
 720                         if (!critical.Define ()) {
 721                                 throw new NotImplementedException ();
 722                         }
 723
 724                         var temp_critical = new LocalTemporary (critical.TypeSpec);
 725                         var label_critical = ec.DefineLabel ();
 726                         var label_end = ec.DefineLabel ();
 727
 728                         //
 729                         // Special path for dynamic awaiters
 730                         //
 731                         // var awaiter = this.$awaiter as ICriticalNotifyCompletion;
 732                         // if (awaiter == null) {
 733                         //    var completion = (INotifyCompletion) this.$awaiter;
 734                         //    this.$builder.AwaitOnCompleted (ref completion, ref this);
 735                         // } else {
 736                         //    this.$builder.AwaitUnsafeOnCompleted (ref awaiter, ref this);
 737                         // }
 738                         //
 739                         awaiter.Emit (ec);
 740                         ec.Emit (OpCodes.Isinst, critical.TypeSpec);
 741                         temp_critical.Store (ec);
 742                         temp_critical.Emit (ec);
 743                         ec.Emit (OpCodes.Brtrue_S, label_critical);
 744
 745                         var temp = new LocalTemporary (Module.PredefinedTypes.INotifyCompletion.TypeSpec);
 746                         awaiter.Emit (ec);
 747                         ec.Emit (OpCodes.Castclass, temp.Type);
 748                         temp.Store (ec);
 749                         EmitOnCompleted (ec, temp, false);
 750                         temp.Release (ec);
 751                         ec.Emit (OpCodes.Br_S, label_end);
 752
 753                         ec.MarkLabel (label_critical);
 754
 755                         EmitOnCompleted (ec, temp_critical, true);
 756
 757                         ec.MarkLabel (label_end);
 758
 759                         temp_critical.Release (ec);
 760                 }
 761
 762                 public void EmitAwaitOnCompleted (EmitContext ec, FieldExpr awaiter)
 763                 {
 764                         bool unsafe_version = false;
 765                         if (Module.PredefinedTypes.ICriticalNotifyCompletion.Define ()) {
 766                                 unsafe_version = awaiter.Type.ImplementsInterface (Module.PredefinedTypes.ICriticalNotifyCompletion.TypeSpec, false);
 767                         }
 768
 769                         EmitOnCompleted (ec, awaiter, unsafe_version);
 770                 }
 771
 772                 void EmitOnCompleted (EmitContext ec, Expression awaiter, bool unsafeVersion)
 773                 {
 774                         var pm = Module.PredefinedMembers;
 775                         PredefinedMember<MethodSpec> predefined;
 776                         bool has_task_return_type = false;
 777                         if (return_type.Kind == MemberKind.Void) {
 778                                 predefined = unsafeVersion ? pm.AsyncVoidMethodBuilderOnCompletedUnsafe : pm.AsyncVoidMethodBuilderOnCompleted;
 779                         } else if (return_type == Module.PredefinedTypes.Task.TypeSpec) {
 780                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderOnCompletedUnsafe : pm.AsyncTaskMethodBuilderOnCompleted;
 781                         } else {
 782                                 predefined = unsafeVersion ? pm.AsyncTaskMethodBuilderGenericOnCompletedUnsafe : pm.AsyncTaskMethodBuilderGenericOnCompleted;
 783                                 has_task_return_type = true;
 784                         }
 785
 786                         var on_completed = predefined.Resolve (Location);
 787                         if (on_completed == null)
 788                                 return;
 789
 790                         if (has_task_return_type)
 791                                 on_completed = MemberCache.GetMember<MethodSpec> (set_result.DeclaringType, on_completed);
 792
 793                         on_completed = on_completed.MakeGenericMethod (this, awaiter.Type, ec.CurrentType);
 794
 795                         var mg = MethodGroupExpr.CreatePredefined (on_completed, on_completed.DeclaringType, Location);
 796                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 797                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 798                         };
 799
 800                         var args = new Arguments (2);
 801                         args.Add (new Argument (awaiter, Argument.AType.Ref));
 802                         args.Add (new Argument (new CompilerGeneratedThis (CurrentType, Location), Argument.AType.Ref));
 803                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 804                                 mg.EmitCall (ec, args);
 805                         }
 806                 }
 807
 808                 public void EmitInitializer (EmitContext ec)
 809                 {
 810                         //
 811                         // Some predefined types are missing
 812                         //
 813                         if (builder == null)
 814                                 return;
 815
 816                         var instance = (TemporaryVariableReference) Instance;
 817                         var builder_field = builder.Spec;
 818                         if (MemberName.Arity > 0) {
 819                                 builder_field = MemberCache.GetMember (instance.Type, builder_field);
 820                         }
 821
 822                         //
 823                         // Inflated factory method when task is of generic type
 824                         //
 825                         if (builder_factory.DeclaringType.IsGeneric) {
 826                                 var task_return_type = return_type.TypeArguments;
 827                                 var bt = builder_factory.DeclaringType.MakeGenericType (Module, task_return_type);
 828                                 builder_factory = MemberCache.GetMember (bt, builder_factory);
 829                                 builder_start = MemberCache.GetMember (bt, builder_start);
 830                         }
 831
 832                         //
 833                         // stateMachine.$builder = AsyncTaskMethodBuilder<{task-type}>.Create();
 834                         //
 835                         instance.AddressOf (ec, AddressOp.Store);
 836                         ec.Emit (OpCodes.Call, builder_factory);
 837                         ec.Emit (OpCodes.Stfld, builder_field);
 838
 839                         //
 840                         // stateMachine.$builder.Start<{storey-type}>(ref stateMachine);
 841                         //
 842                         instance.AddressOf (ec, AddressOp.Store);
 843                         ec.Emit (OpCodes.Ldflda, builder_field);
 844                         if (Task != null)
 845                                 ec.Emit (OpCodes.Dup);
 846                         instance.AddressOf (ec, AddressOp.Store);
 847                         ec.Emit (OpCodes.Call, builder_start.MakeGenericMethod (Module, instance.Type));
 848
 849                         //
 850                         // Emits return stateMachine.$builder.Task;
 851                         //
 852                         if (Task != null) {
 853                                 var task_get = Task.Get;
 854
 855                                 if (MemberName.Arity > 0) {
 856                                         task_get = MemberCache.GetMember (builder_field.MemberType, task_get);
 857                                 }
 858
 859                                 var pe_task = new PropertyExpr (Task, Location) {
 860                                         InstanceExpression = EmptyExpression.Null,      // Comes from the dup above
 861                                         Getter = task_get
 862                                 };
 863
 864                                 pe_task.Emit (ec);
 865                         }
 866                 }
 867
 868                 public void EmitSetException (EmitContext ec, LocalVariableReference exceptionVariable)
 869                 {
 870                         //
 871                         // $builder.SetException (Exception)
 872                         //
 873                         var mg = MethodGroupExpr.CreatePredefined (set_exception, set_exception.DeclaringType, Location);
 874                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 875                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 876                         };
 877
 878                         Arguments args = new Arguments (1);
 879                         args.Add (new Argument (exceptionVariable));
 880
 881                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 882                                 mg.EmitCall (ec, args);
 883                         }
 884                 }
 885
 886                 public void EmitSetResult (EmitContext ec)
 887                 {
 888                         //
 889                         // $builder.SetResult ();
 890                         // $builder.SetResult<return-type> (value);
 891                         //
 892                         var mg = MethodGroupExpr.CreatePredefined (set_result, set_result.DeclaringType, Location);
 893                         mg.InstanceExpression = new FieldExpr (builder, Location) {
 894                                 InstanceExpression = new CompilerGeneratedThis (ec.CurrentType, Location)
 895                         };
 896
 897                         Arguments args;
 898                         if (HoistedReturnValue == null) {
 899                                 args = new Arguments (0);
 900                         } else {
 901                                 args = new Arguments (1);
 902                                 args.Add (new Argument (HoistedReturnValue));
 903                         }
 904
 905                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 906                                 mg.EmitCall (ec, args);
 907                         }
 908                 }
 909
 910                 protected override TypeSpec[] ResolveBaseTypes (out FullNamedExpression base_class)
 911                 {
 912                         base_type = Compiler.BuiltinTypes.ValueType;
 913                         base_class = null;
 914
 915                         var istate_machine = Module.PredefinedTypes.IAsyncStateMachine;
 916                         if (istate_machine.Define ()) {
 917                                 return new[] { istate_machine.TypeSpec };
 918                         }
 919
 920                         return null;
 921                 }
 922         }
 923
 924         public class StackFieldExpr : FieldExpr, IExpressionCleanup
 925         {
 926                 public StackFieldExpr (Field field)
 927                         : base (field, Location.Null)
 928                 {
 929                 }
 930
 931                 public bool IsAvailableForReuse {
 932                         get {
 933                                 var field = (Field) spec.MemberDefinition;
 934                                 return field.IsAvailableForReuse;
 935                         }
 936                         set {
 937                                 var field = (Field) spec.MemberDefinition;
 938                                 field.IsAvailableForReuse = value;
 939                         }
 940                 }
 941
 942                 public override void AddressOf (EmitContext ec, AddressOp mode)
 943                 {
 944                         base.AddressOf (ec, mode);
 945
 946                         if (mode == AddressOp.Load) {
 947                                 IsAvailableForReuse = true;
 948                         }
 949                 }
 950
 951                 public override void Emit (EmitContext ec)
 952                 {
 953                         base.Emit (ec);
 954
 955                         PrepareCleanup (ec);
 956                 }
 957
 958                 public void EmitLoad (EmitContext ec)
 959                 {
 960                         base.Emit (ec);
 961                 }
 962
 963                 public void PrepareCleanup (EmitContext ec)
 964                 {
 965                         IsAvailableForReuse = true;
 966
 967                         //
 968                         // Release any captured reference type stack variables
 969                         // to imitate real stack behavour and help GC stuff early
 970                         //
 971                         if (TypeSpec.IsReferenceType (type)) {
 972                                 ec.AddStatementEpilog (this);
 973                         }
 974                 }
 975
 976                 void IExpressionCleanup.EmitCleanup (EmitContext ec)
 977                 {
 978                         EmitAssign (ec, new NullConstant (type, loc), false, false);
 979                 }
 980         }
 981 }