c# - Whats the overhead of await without I/O -

one downside of async pattern in c# 5 tasks not covariant, i.e there no itask<out tresult>

i have noticed devs do

return await someasyncmethod();  

to come around this.

exactly impact performance wise crate? there no i/o or thread yield await , cast correct covariant, async framework under hood in case? there thread context switch?

edit: more info, code wont compile

public class listproductsqueryhandler : iqueryhandler<listproductsquery, ienumerable<product>> {     private readonly ibusinesscontext _context;      public listproductsqueryhandler(ibusinesscontext context)     {         _context = context;     }      public task<ienumerable<product>> handle(listproductsquery query)     {         return _context.dbset<product>().tolistasync();     } } 

beacuse task not covariant adding await , cast correct ienumerable instead of list tolistasync returns

configureawait(false) everywhere in domain code not feel viable solution use lowlever methods like

public async task<object> invoke(query query) {     var dtotype = query.gettype();     var resulttype = getresulttype(dtotype.basetype);     var handler = _container.getinstance(typeof(iqueryhandler<,>).makegenerictype(dtotype, resulttype)) dynamic;     return await handler.handle(query dynamic).configureawait(false); } 

the more notable cost of approach solving problem if there value in synchronizationcontext.current need post value , wait schedule work. if context busy doing other work, waiting time when don't actually need in context.

that can avoided using configureawait(false), while still keeping method async.

once you've removed possibility of using sync context, state machine generated async method shouldn't have overhead that's notably higher you'd need provide when adding continuation explicitly.