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Cand sa folosim System.Thread.Timer

In .NET putem sa alegem din 3 tipuri de timer:
System.Windows.Forms.Timer se foloseste in general pe UI, cand trebuie sa facem update. System.Timer o sa il folosim de obicei de obicei pe partea de server cand vrem mai multe flexibilitate si mai mult optiuni. Din cele trei timer-uri, acesta are cele mai multe optiuni.
System.Thread.Timer, care rulează un nou thread pentru operațiile sale. Acesta este folositor când vrem sa facem operații asyncron.
System.Threading.Timer timer = new System.Threading.Timer(new TimerCallback(ExecutaCeva), null, 0, 2000);
...
private void ExecutaCeva(object obj)
{
....
}
Pentru a face disable/enable putem sa folosim:
timer.Change(Timeout.Infinite, Timeout.Infinite); //Disable.
timer.Change(0, 2000); //Enable.
Cea ce mi s-a parut foarte folositor la acest imer sunt parametrii lui Change si ultimii doi parametrii a contructorului. Prin intermediul lor putem sa specificam dupa ce perioada sa se apeleze metoda ExecutaCeva, iar apoi la ce interval de timp aceasta sa fie executa.
Sunt cazuri cand vrem ca primul apel ExecutaCeva sa fie facut dupa 1 secunda, iar apoi timer-ul sa apeleze aceasta metoda la 10 secunte. Pentru acest lucru daac am folostii System.Timer ar fi nevoie sa oprim timer-ul dupa prima executie, sa setam din nou intervalul de timp, iar apoi sa îl pornim din nou.
System.Thread.Timer ne permite sa facem in felul urmator:
System.Threading.Timer timer = new System.Threading.Timer(new TimerCallback(ExecutaCeva), null, 1000,10000);
varianta care o prefer eu este:
System.Threading.Timer timer = new System.Threading.Timer(new TimerCallback(ExecutaCeva), null, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(10));
Este bine de stiut ca orice moment cand apelam metoda Change, timpul pana cand se apeleaza ExecutaCeva se modifica. Daca prima valoare este 0, atunci metoda pentru callback se apeleaza imediat, iar daca este Timer.Infinite atunci timer-ul este disable.
Cand al doilea parametru este 0 sau Timer.Infine, atuci timer-ul se executa o singura data.

Comments

  1. N-am inteles niciodata de ce e nevoie de jdemii de Timeri sau macar de ce nu implementeaza aceeasi interfata.
    O alta solutie, mai .Net 4.0 este sa folosesti Taskuri:
    _cancellationTokenSource = new CancellationTokenSource();
    Task<T>.Factory.StartNew(new Action(()=>Thread.Sleep(timerInterval)),_cancellationTokenSource.Token).ContinueWith(myAction,_cancellationTokenSource.Token);
    Codul asta incepe un task care asteapta timerInterval, apoi executa myAction. Se poate da cancel la toata chestia cu _cancellationTokenSource.Dispose().

    ReplyDelete
  2. Fiecare soi de timer are rostul lui, in anumite cazuri: System.Windows.Forms.Timer e timer-ul "clasic" care foloseste intern functia SetTimer() din WindowsSDK si se bazeaza pe procesarea in message loop a mesajului de WM_TIMER

    - avantaje: e gestionat de sistemul de operare, nu consuma un thread separat (ci in UI thread), e mai simplu de utilizat

    - dezavantaje: rezolutie redusa (55ms pe Win95/08, 10-15ms pe Win2000/XP/Vista etc.), WM_TIMER e un mesaj low priority, deci poate fi procesat cu intarziere daca sunt mesaje mai prioritare in coada; numarul maxim de timere care poate fi creat e limitat (mai mult pe versiunile vechi de Windows, pe cele mai noi limita e destul de mare); trebuie avut grija sa se apeleze Dispose() la sfarsit.

    Celelalte doua clase Timer se bazeaza pe threads, si deja sunt alta mancare de peste. O comparatie buna se gaseste in articolul lui Alex Calvo:
    http://msdn.microsoft.com/en-us/magazine/cc164015.aspx

    ReplyDelete
  3. Tudor: multumesc de link, articolul a fost foarte interesant.
    Siderite: interesant mod de a folosii task-urile. O sa studiez problema zilele astea, cea ce nu imi este clar, daca prin apelul la ContinueWith se continua pe acelasi thread sau pe un thread separat. O sa revin cu mai multe informatii zilele acestea.

    ReplyDelete

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