CODEWITHSUNDEEP
c#
user1590636
user1590636

Reputation: 1194

2 threads increasing a static integer

if i am increasing a static by 2 different Tasks or Threads do i need to lock it?

i have this class which will be used by multiple threads at the same time, it returns a proxy to be used inside a thread but i dont want to use the same proxy at the same time with each thread, so i thought incrementing a static integer is the best way, any suggestions?

class ProxyManager
{
    //static variabl gets increased every Time GetProxy() gets called
    private static int Selectionindex;
    //list of proxies
    public static readonly string[] proxies = {};
    //returns a web proxy
    public static WebProxy GetProxy()
    {
      Selectionindex = Selectionindex < proxies.Count()?Selectionindex++:0;
      return new WebProxy(proxies[Selectionindex]) { Credentials = new NetworkCredential("xxx", "xxx") };
    }
}

based on the selected answer

if(Interlocked.Read(ref Selectionindex) < proxies.Count())
{
    Interlocked.Increment(ref Selectionindex);
}
else
{
    Interlocked.Exchange(ref Selectionindex, 0);
}

Selectionindex = Interlocked.Read(ref Selectionindex);

Upvotes: 4

Views: 268

Answers (1)

cfeduke
cfeduke

Reputation: 23236

If you increment a static variable across threads you will end up with inconsistent results. Instead use Interlocked.Increment:

private void IncrementSelectionIndex() {
    Interlocked.Increment(ref Selectionindex);
}

64-bit reads are atomic, but to fully support 32-bit systems you should use Interlocked.Read

private void RetrieveSelectionIndex() {
    Interlocked.Read(ref Selectionindex);
}

Upvotes: 5

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