Because ArrayHandle currently only supports one device at a time, it is
possible that a `PrepareForInput` might actually need to wait for write
access so that it could move the data between devices. However, we don't
want the `Token` to be attached for writing because that could block
other read operations.
To get around this, add a hack to WaitToWrite to allow it to attach for
reading instead of writing.
An issue that was identified for the thread safety of `ArrayHandle` is
that if several threads are waiting to use an `ArrayHandle`, there might
be an expectation of the order in which the operations happen. For
example, if one thread is modifying the contents of an `ArrayHandle` and
another is reading those results, we would need the first one to start
before the second one.
To solve this, a queue is added to `ArrayHandle` such that when waiting
to read or write an `ArrayHandle` the `Token` has to be at the top of
the queue in addition to other requirements being met.
Additionally, an `Enqueue` method is added to add a `Token` to the queue
without blocking. This allows a control thread to queue the access and
then spawn a thread where the actual work will be done. As long as
everything is enqueued on the main thread, the operations will happen in
the expected order.
Previously, when a ReadPortal or a WritePortal was returned from an
ArrayHandle, it had wrapped in it a Token that was attached to the
ArrayHandle. This Token would prevent other reads and writes from the
ArrayHandle.
This added safety in the form of making sure that the ArrayPortal was
always valid. Unfortunately, it also made deadlocks very easy. They
happened when an ArrayPortal did not leave scope immediately after use
(which is not all that uncommon).
Now, the ArrayPortal no longer locks up the ArrayHandle. Instead, when
an access happens on the ArrayPortal, it checks to make sure that
nothing has happened to the data being accessed. If it has, a fatal
error is reported to the log.
To get a portal to access ArrayHandle values in the control
environment, you now use the ReadPortal and WritePortal methods.
The portals returned are wrapped in an ArrayPortalToken object
so that the data between the portal and the ArrayHandle are
guaranteed to be consistent.
When a single `ArrayHandle` is given to multiple arguments of a worklet
dispatch, the `PrepareFor*` methods will be called multiple times with
the same token. If one of them is a `PrepareForInPlace` or
`PrepareForOutput`, then the two requests will deadlock. To prevent
this, allow the `PrepareFor*` to happen if the same token was used
previously.
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.
Duplicated the new versions of PrepareFor* methods from the basic
ArrayHandle that take a token in addition to the other arguments. The
ArrayHandle attaches itself to the token and will not allow operaitons
that make the returned portal invalid until the token goes out of scope.
Later the old versions will be deprecated.
When it was originally created, it was assumed that the ArrayHandle
class would be used by a single thread. As the use of VTK-m expands,
that is no longer a safe assumption. To ensure that operations on
ArrayHandle happen correctly, add a mutex to the Internals of
ArrayHandle and require all operations on the Internals lock that mutex.
This adds an ExecutionSignature tag named Device that passes the
DeviceAdapterTag as an argument to the worklet's operator(). This allows
worklets to specialize their code based on the device.
Previously memory that was allocated outside of VTK-m was impossible to transfer to
VTK-m as we didn't know how to free it. By extending the ArrayHandle constructors
to support a Storage object that is being moved, we can clearly express that
the ArrayHandle now owns memory it didn't allocate.
Here is an example of how this is done:
```cpp
T* buffer = new T[100];
auto user_free_function = [](void* ptr) { delete[] static_cast<T*>(ptr); };
vtkm::cont::internal::Storage<T, vtkm::cont::StorageTagBasic>
storage(buffer, 100, user_free_function);
vtkm::cont::ArrayHandle<T> arrayHandle(std::move(storage));
```
Sandia National Laboratories recently changed management from the
Sandia Corporation to the National Technology & Engineering Solutions
of Sandia, LLC (NTESS). The copyright statements need to be updated
accordingly.
The basic storage has an implicit invariant that if the size of the
storage is 0 then the array is a null pointer. That invariant was broken
if the array was allocated and then Shrink or Allocate was called with
0. In that case, the array remained allocated by the size was set to 0.
This fixes the problem by making sure a Shrink(0) actually does an
Allocate(0) (to clear out the data) and that the basic storage always
frees its memory when allocating a 0 sized array.
58bbeb18 Support using empty array handles as input
6d5de0c3 Change make_ArrayHandle work with empty std::vector
Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Robert Maynard <robert.maynard@kitware.com>
Merge-request: !694
Previously if you constructed an array handle without allocating it, you
would get an error if you tried to use the array as input. This
conflicted with some recent changes to accept empty vectors.
Now when you try to use an unallocated ArrayHandle as input (calling
PrepareForInput or PrepareForInPlace), it internally calls Allocate(0)
(to establish internal state) and sets up a valid execution ArrayPortal
of size 0.
