How to properly lock a value type?

Question

I was reading about threading and about locking. It is common practise that you can't (well should not) lock a value type.

So the question is, what is the recommended way of locking a value type? I know there's a few ways to go about doing one thing but I haven't seen an example. Although there was a good thread on MSDN forums but I can't seem to find that now.

Thanks

Answer 1

Use another object for the lock.

int valueType;
object valueTypeLock = new object();

void Foo()
{
    lock (valueTypeLock)
    {
        valueType = 0;
    }
}

Answer 2

Depend on your situation you might be able to avoid using locks by leveraging System.Threading.Interlocked the same code in Jon's example becomes:

System.Threading.Interlocked.Exchange(valueType,0)

Answer 3

Your question is worded in such a way that it suggests to me that you don't entirely understand locking. You don't lock the data, you lock to protect the integrity of the data. The object you lock on is inconsequential. What matters is that you lock on the same object in other areas of your code that alter the data being protected.

HTH, Kent

Answer 4

I'm always using a separate variable to lock on:

object syncObj = new object();

void Foo()
{
  lock(syncObj)
  {
    // do some stuff
  }
}

Locking on value-types doesn't make sense anyway because value-types are immutable and can't be modified. Locking on 'this' is also problematic because 'this' is visible to the outer world.

For some information about how the Monitor was originally intended to be used see Monitor (synchronization)