Errors and warnings related to the lock statement and thread synchronization

  • Article

There are a few errors related to the lock statement and thread synchronization:

  • CS0185: 'type' is not a reference type as required by the lock statement.
  • CS1996: Cannot await in the body of a lock statement
  • CS9217: A lock statement on a value of type 'System.Threading.Lock' cannot be used in async methods or async lambda expressions.

In addition, the compiler might produce the following warning related to lock statements and thread synchronization:

  • CS9216: A value of type System.Threading.Lock converted to a different type will use likely unintended monitor-based locking in lock statement.

lock statement errors

  • CS0185: 'type' is not a reference type as required by the lock statement.
  • CS1996: Cannot await in the body of a lock statement
  • CS9217: A lock statement on a value of type 'System.Threading.Lock' cannot be used in async methods or async lambda expressions.

These errors indicate that your code violates rules regarding the lock the statement:

  • The object being locked must be a reference types. Value types aren't allowed.
  • An await expression can't be used in the scope of a lock statement.
  • The lock statement can't be used with async methods or lambda expressions. For this error, you can replace the type of object locked with a different type. The lock statement uses the Monitor API.

You must update your code to follow the rules of the lock statement.

lock warning

  • CS9216: A value of type System.Threading.Lock converted to a different type will use likely unintended monitor-based locking in lock statement.

Beginning with C# 13, the lock generates specialized code when the target object is a System.Threading.Lock object. The compiler generates this warning when you're using a Lock object, but your code converts its type to something else. Therefore, the compiler generates the general locking code, not the locking code specific to the Lock type. For example:

object lockObject = new System.Threading.Lock();

lock (lockObject) // CS9216
{
    // .. Your code
}

You should ensure the variable or expression represents the type of the Lock object.