CODEWITHSUNDEEP
c#singletonthread-safety
TalentTuner
TalentTuner

Reputation: 17556

Singleton Instance

I know there are lot of ways to implement a thread safe singleton pattern like (Double Check Locking , static readonly method, lock method) but i just tried below code 

static void Main(string[] args)
{           
    for (int i = 0; i <= 100; i++)
    {
        Thread t = new Thread(new ParameterizedThreadStart(doSome));
        t.Start(null);               
    }
    Console.ReadLine();
}

private static void doSome(object obj)
{           
    MyReadOnly obj1 = MyReadOnly.getInstance;
    Console.WriteLine(obj1.GetHashCode().ToString());
}   

class MyReadOnly
{
    private static  MyReadOnly instance  = new MyReadOnly();
    int counter = 0;

   // static MyReadOnly()
   // {
   // }  treat is as commented code.

    public static MyReadOnly getInstance { get { return instance; } }
    private MyReadOnly()
    {
        Console.WriteLine((++counter).ToString());
    }       
}

when i see the output of this program , i see just single object created (because of same hashcode)

how to prove that this code is not thread safe?

EDIT

removing static constructor which causes some confusion

Upvotes: 1

Views: 321

Answers (2)

Jon Skeet
Jon Skeet

Reputation: 1499770

That code is thread-safe due to the nature of type initializers in .NET. The type initializer is guaranteed to run exactly once, and if two threads try to run it at the same time, one will do so and the other will block.

See my article on singleton implementation for more details.

Upvotes: 6

VinayC
VinayC

Reputation: 49165

This is actually thread-safe code because you are (indirectly) using static constructor to create the instance (And CLR guarantees invocation of static constructor is thread-safe manner on/before access to any other type member).

Upvotes: 2

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