With the major revision 2.0 of VTK-m, many items previously marked as
deprecated were removed. If updating to a new version of VTK-m, it is
recommended to first update to VTK-m 1.9, which will include the deprecated
features but provide warnings (with the right compiler) that will point to
the replacement code. Once the deprecations have been fixed, updating to
2.0 should be smoother.
Some (but not all) versions of visual studio seem to have a bug that
causes a syntax error when using the deprecated attribute in a templated
constructor.
The actual code for AtomicArrayExecutionObject does not need to be
specialized by the device. The functionality is implemented by calling
the vtkm::Atomic* methods, which are properly implemented on each
device.
The old atomic compare and swap operations (`vtkm::AtomicCompareAndSwap`
and `vtkm::exec::AtomicArrayExecutionObject::CompareAndSwap`) had an
order of arguments that was confusing. The order of the arguments was
shared pointer (or index), desired value, expected value. Most people
probably assume expected value comes before desired value. And this
order conflicts with the order in the `std` methods, GCC atomics, and
Kokkos.
Change the interface of atomic operations to be patterned off the
`std::atomic_compare_exchange` and `std::atomic<T>::compare_exchange`
methods. First, these methods have a more intuitive order of parameters
(shared pointer, expected, desired). Second, rather than take a value
for the expected and return the actual old value, they take a pointer to
the expected value (or reference in `AtomicArrayExecutionObject`) and
modify this value in the case that it does not match the actual value.
This makes it harder to mix up the expected and desired parameters.
Also, because the methods return a bool indicating whether the value was
changed, there is an additional benefit that compare-exchange loops are
implemented easier.
For example, consider you want to apply the function `MyOp` on a
`sharedValue` atomically. With the old interface, you would have to do
something like this.
```cpp
T oldValue;
T newValue;
do
{
oldValue = *sharedValue;
newValue = MyOp(oldValue);
} while (vtkm::AtomicCompareAndSwap(sharedValue, newValue, oldValue) != oldValue);
```
With the new interface, this is simplfied to this.
```cpp
T oldValue = *sharedValue;
while (!vtkm::AtomicCompareExchange(sharedValue, &oldValue, MyOp(oldValue));
```
Previously vtk-m allowed users to issue atomic loads on constant
values which is problematic for the following reasons:
- can be a source of undefined behavior
- not supported by kokkos
This issue was detected when using kokkos HIP atomic implementation
Now that we have the functions in `vtkm/Atomic.h`, we can deprecate (and
eventually remove) the more cumbersome classes `AtomicInterfaceControl`
and `AtomicInterfaceExecution`.
Also reversed the order of the `expected` and `desired` parameters of
`vtkm::AtomicCompareAndSwap`. I think the former order makes more sense
and matches more other implementations (such as `std::atomic` and the
GCC `__atomic` built ins). However, there are still some non-deprecated
classes with similar methods that cannot easily be switched. Thus, it's
better to be inconsistent with most other libraries and consistent with
ourself than to be inconsitent with ourself.
The old version of ExecutionObject (that only takes a device) is still
supported, but you will get a deprecated warning if that is what is
defined.
Supporing this also included sending vtkm::cont::Token through the
vtkm::cont::arg::Transport mechanism, which was a change that propogated
through a lot of code.
The collection of connectivity algorithms had a couple of inefficiencies.
By moving to using WorkId we can remove a couple of arrays of the same size
as the input domain. In addition by moving to using atomics we can remove
an bool output array with a size equivalent to the input domain and
a call to reduce.
- Use AtomicInterface to implement device-specific atomic operations.
- Remove DeviceAdapterAtomicArrayImplementations.
- Extend supported atomic types to include unsigned 32/64-bit ints.
- Add a static_assert to check that AtomicArray type is supported.
- Add documentation for AtomicArrayExecutionObject, including a CAS
example.
- Add a `T Get(idx)` method to AtomicArrayExecutionObject that does
an atomic load, and update existing CAS usage to use this instead
of `Add(idx, 0)`.
