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Short brief - Request-Response, Asynchron and Fire and Forget patterns

Un apel spre un serviciu poate sa fie facut in diferite moduri. Cele mai uzuale moduri sunt cele care respecta paternul Request-Response si Asynchron. Pe langa aceste doua paternuri mai exista inca unul, dar care este mai rar folosit Fire and Forget.
Request-Response pattern- se refera la faptul ca pentru fiecare request facut se asteapta raspunsul.
Response response = service.CallService(request)
Asynchron pattern - este un patern bazat pe evenimente. Odata ce un apel a fost facut, aplicatia nu asteapta raspunsul de la server. Cel care face apelul trebuie sa se inregistreze la un eveniment care o sa fie declansat cand raspunsul soseste.
service.ResponseEvent += new EventHandler(ResponseReceived);
service.CallServiceAsync(request);
Fire and Forget pattern - este destul de asemanator cu paternul Asynchron, doar ca odata comanda trimisa nu ne mai intereseaza ce se intampla cu aceasta.
service.CalService(request);    // Metoda nu returneaza nimica
Exista diferite scenarii cand Fire and Forget este recomandat sa fie folosit. Conditia principala care trebuie sa fie implinita ca sa putem folostii acest patern este ca sa ne putem asigura ca request-ul ajunge la server - avem un protocol ce ne garanteaza ca mesajele au ajuns la destinatie( de exemplu daca folosim cozi de mesaje care ne asigura ca mesajele nu se pierd - de exemplul MQ).
In cazul in care avem servicii cu un volum mare de request-uri, atunci poate pentru unele tipuri de request-uri putem sa folosim acest patern. De exemplu pentru cele in care rezultatul este format din mesaje precum Okay.
Cele mai mari dezavantaje apar in momentul in care ceva nu functioneaza bine. Debug-ul este destul de complicat si de obicei necesita interventia umana pentru a putea gasi problema. Problemele care pot sa apara sunt la nivelului protocolului care ar trebui sa ne garanteze ca mesajele ajung la destinatie.
Un alt mod de a apela un serviciu este de a face unu sau mai multe request-uri de tipul Fire and Forget, iar apoi la un moment dat sa se verifice daca a venit un raspuns( intr-un cache, in baza de date etc) - in cazul in care raspunsul se pune intr-o locatie unde atat clientul cat si serverul le pot accesa
Nu trebuie confundat un apel de forma:
service.CallService(request,()=>{ ... });
ca si cum ar fi un apel de tip Fire and Forget. Orice metoda sau lambda expresion specificata ca si al doilea parametru care este apelata in momentul in care raspunsul soseste de la server reprezinta un apel de tip asincron.

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