Weird situation with lock field being null - c# probably .net 4.0 win8-32 specific

Question

I have the following code:

public class Settings
{
    private object _lock = new object();
    public void Save() {
        lock (_lock)
        {
        ...
        }
    }
}

On windows 8 x86 / .net 4.0 lock throws exception:

Exception Type:        System.ArgumentNullException
Exception Message:     Value cannot be null.
Exception Target Site: ReliableEnter 

I attached debugger and its null. _lock is really null :|

On windows 7 x64 it works all right. I am checking other OSes now.

EDIT:

It is realted to deserialization. After deserialization of Settings class _lock is null. _lock field didn't exist at the time of serilization of settings and its getting back deserialized as null. Deleting serilized object file and recreating it with lock field eliminated exception. I will check if this is correct deserialization behavior if field didin't exist at serialization. Overwriting object value initialized in declaration doesn't look cool to me. But thats pretty much answer to this. I admit that I didn't consider serialization, deserialization at the time I asked for help ;).

EDIT2: Here is the code that ilustrates my scenario and what was happening to me:

1. Serilize class without _lock field

   class Program
   {
       static void Main(string[] args)
       {
           Settings set = new Settings();
   
           using (FileStream fs = new FileStream(@"C:\test\tst.set", FileMode.Create, FileAccess.Write, FileShare.None))
           {
               BinaryFormatter bf = new BinaryFormatter();
               bf.Serialize(fs, set);
               fs.Flush();
               fs.Close();
           }
       }
   }
   
   [Serializable]
   internal class Settings
   {
       private int _i = 12;
   
   
       public void testMethod()
       {
   
           int i = 0;
           i++;
           Console.WriteLine(i);
   
       }
   }
   

2. Deserialize to class with lock field and call testMethod:

   class Program
   {
       static void Main(string[] args)
       {
           Settings set = null;
           using (FileStream fs = new FileStream(@"C:\test\tst.set", FileMode.Open, FileAccess.Read, FileShare.Read))
           {
               BinaryFormatter bf = new BinaryFormatter();
               set = (Settings)bf.Deserialize(fs);
               fs.Flush();
               fs.Close();
           }
   
           set.testMethod();
       }
   }
   
   [Serializable]
   internal class Settings
   {
       private int _i = 12;
       private readonly object _lock = new object();
   
       public void testMethod()
       {
           lock (_lock)
           {
               int i = 0;
               i++;
               Console.WriteLine(i);
           }
       }
   }
   

program will crash on testMethod call.

I didin't find anything related to this behavior in documentaion. I will check for null after deserialization and that will end my trouble.

Ok. How deserilization can assign null to my readonly field assigned on declaration?

Answer 1

To all intents and purposes, if you set it to a new Object and you don't change it anywhere else, then what you're seeing is impossible.

First thing I'd try is to move the new Object code into my constructor, if it's happy there, then leave it be. Either way, trace over the assignment and see if it ever got assigned.

Make sure your IDE is not watching anything that could effect the value of the variable as a side effect - check conditional breakpoints for the same thing.

Note that you can create a conditional break point on change!

If still broken add asserts, compile in debug - run outside of the IDE.

If the debug version crashes when the IDE is not part of the mix, take it to other PCs and try it.

If it works on other PCs, Virus scan/reinstall etc. Memory check etc.

The compiler could be broken, try reinstalling Visual Studio.

Then I'm out of ideas!

Answer 2

Private properties are not serialized by default. If you want them to be serialized you need to create your custom serializer methods.

You can look at the following question for extra details