Are Static Fields thread Safe

Question

We have a Static field in a abstract class

ABSTRACT CLASS :-

public abstract class BaseController
{

 private static string a;
 private static string b;

 protected abstract SomeArray[] DoSomeThing();

}

And a derived class

public class Controller1:BaseController
{

      protected override SomeArray[] DoSomthing()
      {
        //////
        In this method we are setting the static variables with different values
      }

}

We also have a class which is starting threads

public class SomeClass 
{

  public SomeClass()
  {
    \\ we are setting the controller we want to call, i mean to decide which base class to call 
  }

   public void Run()
   {
     Thread t  = new Thread(StartThread);
    t.Start();

   }

  public void StartThread()
  {
     _controller.DoSomeThing();
  }

}

All the above service is in a WCF service, and the same client tries to call multiple times which means we have multiple threads running at the same time, we have seen issues where the static variable which we are setting and using that for some DB update process is sometimes having wrong values

I have read some blogs which says static fields are not thread safe, Can some body please help me understand what could be going wrrong in our code and why we are having some incorrect values passed to the DB.

Answer 1

By definition, a static field or member is shared among all instances of that class, only one instance of that field or member exisits; thus, it is not thread safe.

You have two options, either to synchronize the access (basically, using Monitor class) to that field or to use the ThreadStaticAttribute on that field.

However, i advice to reorganize your class hierarchy so that each class has its own instance of the field or member.

Please note that if there are multiple threads working on the same instance of the class Controller, then we go back to the same problem and you should synchronize access to that instance field.

Good Luck