Question

Example code:

MyObject myObject = new MyObject ();

public void FunA () // accessed from thread 1 (when user click a button)
{
    myObject = null;
    // do some stuff
    myObject = new MyObject ( someNewValues );
}

public void FunB () // accessed from thread 2 (calling using timer or smth.)
{
    int x = myObject.ReadX ();
}

In most cases it works OK, but when FunA will make myObject null and in same time FunB will access it, application will crash.

Question: How to do that, when thread 1 will access FunA, thread 2 cannot enter FunB?

Update: I tried locks before, but the problem is FunB is calling event to thread 1 (GUI) (guiForm.Invoke) and thread 1 will stuck before FunA { lock… }.

Answer 1

You can lock myObject so that only the current thread can use it.

public void FunA () // accessed from thread 1 (when user click a button)
{
  lock(myObject)
    {
       myObject = null;
       // do some stuff
       myObject = new MyObject ( someNewValues );
    }
}

This will prevent FunB from accessing myObject until it has been released by the lock.

Update

As pointed out in the comments, it’s probably not a good idea to modify the object that you have a lock on. In this case you can simply have an object that you lock and an object that you modify such that:

var lockObj = new object();
var myObject = new MyObject();


public void FunA () // accessed from thread 1 (when user click a button)
{
  lock(lockObj)
    {
       myObject = null;
       // do some stuff
       myObject = new MyObject ( someNewValues );
    }
}

public void FunB () // accessed from thread 2 (calling using timer or smth.)
{
    lock(lockObj)
    {
       int x = myObject.ReadX ();
    }
}