public void EmitPrologue(EmitContext ec)
{
var fe_awaiter = new FieldExpr(awaiter, loc);
fe_awaiter.InstanceExpression = new CompilerGeneratedThis(ec.CurrentType, loc);
//
// awaiter = expr.GetAwaiter ();
//
fe_awaiter.EmitAssign(ec, expr, false, false);
is_completed.InstanceExpression = fe_awaiter;
is_completed.EmitBranchable(ec, resume_point, true);
var mg_completed = MethodGroupExpr.CreatePredefined(on_completed, fe_awaiter.Type, loc);
mg_completed.InstanceExpression = fe_awaiter;
var args = new Arguments(1);
var storey = (AsyncTaskStorey)machine_initializer.Storey;
var fe_cont = new FieldExpr(storey.Continuation, loc);
fe_cont.InstanceExpression = new CompilerGeneratedThis(ec.CurrentType, loc);
args.Add(new Argument(fe_cont));
//
// awaiter.OnCompleted (continuation);
//
mg_completed.EmitCall(ec, args);
base.DoEmit(ec);
}
public void EmitPrologue(EmitContext ec)
{
var fe_awaiter = new FieldExpr(awaiter, loc);
fe_awaiter.InstanceExpression = new CompilerGeneratedThis(ec.CurrentType, loc);
//
// awaiter = expr.GetAwaiter ();
//
fe_awaiter.EmitAssign(ec, expr, false, false);
Label skip_continuation = ec.DefineLabel();
is_completed.InstanceExpression = fe_awaiter;
is_completed.EmitBranchable(ec, skip_continuation, true);
base.DoEmit(ec);
FieldSpec[] stack_fields = null;
TypeSpec[] stack = null;
//
// Here is the clever bit. We know that await statement has to yield the control
// back but it can appear inside almost any expression. This means the stack can
// contain any depth of values and same values have to be present when the continuation
// handles control back.
//
// For example: await a + await b
//
// In this case we fabricate a static stack forwarding method which moves the values
// from the stack to async storey fields. On re-entry point we restore exactly same
// stack using these fields.
//
// We fabricate a static method because we don't want to touch original stack and
// the instance method would require `this' as the first stack value on the stack
//
if (ec.StackHeight > 0)
{
var async_storey = (AsyncTaskStorey)machine_initializer.Storey;
stack = ec.GetStackTypes();
var method = async_storey.GetStackForwarder(stack, out stack_fields);
ec.EmitThis();
ec.Emit(OpCodes.Call, method);
}
var mg_completed = MethodGroupExpr.CreatePredefined(on_completed, fe_awaiter.Type, loc);
mg_completed.InstanceExpression = fe_awaiter;
var args = new Arguments(1);
var storey = (AsyncTaskStorey)machine_initializer.Storey;
var fe_cont = new FieldExpr(storey.Continuation, loc);
fe_cont.InstanceExpression = new CompilerGeneratedThis(ec.CurrentType, loc);
args.Add(new Argument(fe_cont));
//
// awaiter.OnCompleted (continuation);
//
mg_completed.EmitCall(ec, args);
// Return ok
machine_initializer.EmitLeave(ec, unwind_protect);
ec.MarkLabel(resume_point);
if (stack_fields != null)
{
for (int i = 0; i < stack_fields.Length; ++i)
{
ec.EmitThis();
var field = stack_fields[i];
//
// We don't store `this' because it can be easily re-created
//
if (field == null)
{
continue;
}
if (stack[i] is ReferenceContainer)
{
ec.Emit(OpCodes.Ldflda, field);
}
else
{
ec.Emit(OpCodes.Ldfld, field);
}
}
}
ec.MarkLabel(skip_continuation);
}
