Lie, Damn Lie and Documentation

The example to demonstrate how to use AtomicArrayExecutionObject::CompareExchange is mostly incorrect.

  /// ```
  /// AtomicArrayExecutionObject<vtkm::Int32, ...> arr = ...;
  ///
  /// // Compare-exchange multiplication:
  /// vtkm::Int32 current = arr->Get(idx); // Load the current value at idx
  /// do {
  ///   vtkm::Int32 newVal = current * multFactor; // the actual multiplication
  /// } while (!arr->CompareExchange(idx, &current, newVal));
  /// ```

To begin with, arr is not a pointer. Thus to call its Get() method, we should use the . operator rather than ->.

-  /// vtkm::Int32 current = arr->Get(idx); // Load the current value at idx
+  /// vtkm::Int32 current = arr.Get(idx); // Load the current value at idx

The scope of the vtkm::Int32 newVal also ends with the closing braces }, thus would not be accessible in the call to CompareExchange. It needs to be moved to the front of the do keyword.

+ ///   vtkm::Int32 newVal;
  /// do {
- ///   vtkm::Int32 newVal = current * multFactor; // the actual multiplication
+ ///   newVal = current * multFactor; // the actual multiplication
  /// } while (!arr->CompareExchange(idx, &current, newVal));

There is also some issue in the implementation of AtomicCompareExchange that might make this an infinite loop. I will amend the issue once I investigate it further.