Lock on a variable in multiple threads

Question

I am very new to C# and I wanted to ask if I have this situation in MULTI THREADS (pseudo code):

public class ClassA
{
     ClassB c = new ClassB();
     public void someMethod()
     {
          c.myVar = 1;
          // Some other stuff
          c.myVar = 0;
     }
}

public class ClassB
{
     internal int myVar;

     public void MethodA()
     {
        if(myVar = 1)
              myVar = 0;
     }
}

If someMethod() and MethodA() can be active in separate threads, then MethodA() could evaluate the if statement as true; but before it sets myVar = 0, someMethod() sets myVar = 0 making it incorrect to have set myVar to 0 in MethodA()!!

Basically, how do I lock myVar:

• can I lock{} on myVar's property (set, get)
• do I need to use Interlock (I have no experience yet of Interlock though)?

Answer 1

You should create a private object that will allow for locking:

private readonly object _locker = new object();

Then in your property get/set methods, lock around it:

get { lock (_locker) { return this.myVar; } }
set { lock (_locker) { this.myVar = value; } }

Make sure your method uses the lock also:

public void MethodA()
{
    lock(_locker)
    {
        if(myVar == 1)
          myVar = 0;
    }
}