what object type/instance to use for synchronization

Question

I have seen different variations of objects used when acquiring a lock

1. A static private object

   public class MyClass
   {
     private static object syncBlock = new object();
   
     private void MyMethod()
     {
         lock (syncBlock)
         {
   
         }
     }
   

   }

2. A class level private object

   public class MyClass
   {
      private object syncBlock = new object();
   
      private void MyMethod()
      {
          lock (syncBlock)
          {
   
          }
      }
   }
   

3. using the type itself

   public class MyClass
   {
      private void MyMethod()
      {
          lock (typeof (MyClass))
          {
   
          }
      }
   }
   

4. using this:

   public class MyClass
   {
      private void MyMethod()
      {
         lock (this)
         {
   
         }
      }
   }
   

Can someone elaborate what are the pro/cons of each of these and if one should be preferred over others in a given scenario.

Answer 1

Don't use lock(this).

Don't use lock(typeof(MyClass)) either.

As for static vs instance, it depends on what is appropriate for you. If you use a static private object, then all instances of your class will share the lock. If you use a private object that is not static, then each instance will have its own lock. So there is no pro/cons, it depends on what you need.