For the threads example in the concurrency section there is no indication on how assign the constant NULL when running the model after adding the lock. I think it might be a good idea to explicitly state how to run the model.
If I understand correctly both assigning a model variable or an ordinary assignment of, say, -1 would work equally well in this case, but the model variable would be preferable. If that's the case it might also be a good idea to explain the difference between both possibilities.
For the threads example in the concurrency section there is no indication on how assign the constant NULL when running the model after adding the lock. I think it might be a good idea to explicitly state how to run the model.
If I understand correctly both assigning a model variable or an ordinary assignment of, say, -1 would work equally well in this case, but the model variable would be preferable. If that's the case it might also be a good idea to explain the difference between both possibilities.