public void EmitPrologue(EmitContext ec)
{
awaiter = ((AsyncTaskStorey)machine_initializer.Storey).AddAwaiter(expr.Type);
var fe_awaiter = new FieldExpr(awaiter, loc);
fe_awaiter.InstanceExpression = new CompilerGeneratedThis(ec.CurrentType, loc);
Label skip_continuation = ec.DefineLabel();
using (ec.With(BuilderContext.Options.OmitDebugInfo, true)) {
//
// awaiter = expr.GetAwaiter ();
//
fe_awaiter.EmitAssign(ec, expr, false, false);
Expression completed_expr;
if (IsDynamic)
{
var rc = new ResolveContext(ec.MemberContext);
Arguments dargs = new Arguments(1);
dargs.Add(new Argument(fe_awaiter));
completed_expr = new DynamicMemberBinder("IsCompleted", dargs, loc).Resolve(rc);
dargs = new Arguments(1);
dargs.Add(new Argument(completed_expr));
completed_expr = new DynamicConversion(ec.Module.Compiler.BuiltinTypes.Bool, 0, dargs, loc).Resolve(rc);
}
else
{
var pe = PropertyExpr.CreatePredefined(awaiter_definition.IsCompleted, loc);
pe.InstanceExpression = fe_awaiter;
completed_expr = pe;
}
completed_expr.EmitBranchable(ec, skip_continuation, true);
}
base.DoEmit(ec);
//
// The stack has to be empty before calling await continuation. We handle this
// by lifting values which would be left on stack into class fields. The process
// is quite complicated and quite hard to test because any expression can possibly
// leave a value on the stack.
//
// Following assert fails when some of expression called before is missing EmitToField
// or parent expression fails to find await in children expressions
//
ec.AssertEmptyStack();
var storey = (AsyncTaskStorey)machine_initializer.Storey;
if (IsDynamic)
{
storey.EmitAwaitOnCompletedDynamic(ec, fe_awaiter);
}
else
{
storey.EmitAwaitOnCompleted(ec, fe_awaiter);
}
// Return ok
machine_initializer.EmitLeave(ec, unwind_protect);
ec.MarkLabel(resume_point);
ec.MarkLabel(skip_continuation);
}
