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Debugging multithreaded applications in Visual Studio

In postul precedent am povestit putin despre cateva lucruri de baza cand facem debug in Visual Studio. Astazi o sa continuam aceasta discutie si o sa vedem cum putem face debug intr-un mediu multi-thread si multi-processor.
Cand lucram cu mai multe thread-uri, fereastra "Threads" devine cea mai buna prietena a noastra. Prin intermediul acesteia, cand aplicatia ajunge la un breakpoint putem sa vedem toate thread-urile active in procesul nostru. Pentru fiecare thread, putem sa vedem numele acestuia, ID-ul prioritatea si nu in ultimul rand call stack-ul pentru fiecare thread in parte (numele la coloana este "Location"). De foarte multe ori callstack-ul ne ajuta foarte mult nemaifiind nevoie sa selectam cate un thread in parte pentru a vedea callstack-ul.
In momentul cand suntem intr-un breakpoint sa nu uitati ca restul thread-urile ruleaza in continuare. In dreapta acestei ferestre avem un buton "Freeze" prin intermediul caruia putem sa facem freeze la toate thread-urile din procesul nostru. Nu odata mi s-a intamplat ca pana sa investighez codul care rula dintr-un thread, unul sau mai multe thread-uri s-au terminat de executat, iar problema pe care o aveam nu o mai puteam reproduce. Cand un thread este selectat din lista, Visual Studio o sa incerce sa va dupa la codul care se ruleaza pentru thread-ul vostru.

O fereastra asemanatoare exista si pentru procese. In mod normal o sa fiti legati la un sigur proces, caz in care o sa aveti un singur proces in lista. 2 sau mai multe procese pot sa fie active cand aveti mai multe procese selectate de a rula la RUN sau cand va atasati manual la alte procese. 
Toate modulele (assembly-urile) care sunt incarcate intr-un anumit moment pot sa fie vizualizate din fereastra Modules. Aceasta fereastra este folositoare daca aveti probleme cu versiune de assembly sau nu stiti exact ce assembly se incarca si din ce locatie. Aceasta fereastra poate sa deschisa din "Debug->Windows->Modules".
Cand executati codul step cu step si aveti mai multe thread-uri pornite sa nu uitati ca restul thread-urilor ruleza normal daca nu ati facut freeze. Iar in cazul in care un alt thread ajunge la un breakpoint, atunci o sa va intrati pe thread-ul respectiv. Puteti specifica pe un breakpoint pe ce thread sa se activeze (in postul precedent am discutat despre acest lucru).
In cazul in care aveti mai multe thread-uri puteti sa folositi fereastra de "Parallel Stacks" fara nici o problema, chiar daca nu folositi librarie de paralle library. Aceasta va afiseaza un stack pentru modul in care thread-urile au fost create si ce thread pe care il asteapta.
Cand faceti debug incercati ca numarul de thread-uri pe care le aveti pornite sa fie cat mai mic (3-4). Daca o sa aveti prea multe thread-uri pornite, procesul de debug o sa fie destul de complex.
In urmatorul post o sa discutam despre Debugger Canvas.


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