asp.net - More than one await in HttpTaskAsyncHandler -

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httptaskasynchandler nice base-class making async http-handlers in asp.net 4.5 wonder how runtime handles more 1 await statement in processrequestasync.

public class callbackhandler : httptaskasynchandler {     public override async task processrequestasync(httpcontext context)     {         int value1 = await task.factory.startnew(() => 1);         int value2 = await task.factory.startnew(() => 2);         int value3 = await task.factory.startnew(() => 3);          context.response.write(value1 + value2 + value3);     }      public override bool isreusable     {         { return true; }     } }

is iis thread being put on hold 3 times? how test/see this? better wrap 3 awaits in asyn method?

edit: concerned code take iis-workerthread 4 times handle request. if wrap in async method - performe better?

figure msdn mag article jeff prosise

msdn article

this diagram explaining difference between sync , asyn page processing in asp.net. afraid example result in 3 threads being started main worker thread (pink boxes on diagram) , thereby adding overhead.

iis -> task1 tp -> iis -> task2 tp -> iis -> task3 tp -> iis

(task switching main iis wt 4 times)

or compiler smart passes continuation on 1 task next, , returning main thread after 3 tasks done.

iis -> task1 tp -> task2 tp -> task3 tp -> iis

(task switching main iis wt 1 time)

it handles fine.

in iis, have "request context" provided async handler, , async methods default resume in context. whenever await incomplete task, thread returned thread pool (it not blocked), , when task completes, thread pool thread used continue async method after entering request context.

so, no threads "held", request is. putting multiple awaits in async method won't make difference, make difference start multiple tasks , wait them complete, e.g., await task.whenall(task1, task2, task3); (assuming independent, of course).

i don't know of way verify behavior.


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