Expose option to enable fabric memory handle support to Python

[pentschev]

Description

Follow-up to #1743, exposing a way to enable fabric memory handle to Python.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.

[pentschev]

/ok to test

[bdice]

/ok to test

[pentschev]

Definitely not the prettiest way to write this bitwise or, I couldn't find anything much better with Cython though. In pure C++ I would at least have used std::underlying_type_t but that's not exposed to Cython. If anybody has a better idea, please let me know.

[bdice]

We do have a TODO to use an enum class instead of enum, now that we're using Cython 3. That might help here, I'm not sure.

rmm/python/rmm/rmm/librmm/memory_resource.pxd

Line 111 in d750a6e

# TODO: when we adopt Cython 3.0 use enum class

Here's an example of an enum class in Cython from cudf:

https://github.com/rapidsai/cudf/blob/9cd525361c198713a8eaa41fa4d91ad1fe176942/python/pylibcudf/pylibcudf/libcudf/unary.pxd#L13

[pentschev]

We can make the switch but it doesn't seem to help Cython, unfortunately:

      Error compiling Cython file:
      ------------------------------------------------------------
      ...
              # constructor below will raise an error from C++.
              cdef allocation_handle_type descriptor = allocation_handle_type.none
              if enable_ipc:
                  descriptor = descriptor | allocation_handle_type.posix_file_descriptor
              if enable_fabric:
                  descriptor = descriptor | allocation_handle_type.fabric
                                          ^
      ------------------------------------------------------------

      ~/src/rmm/python/rmm/rmm/pylibrmm/memory_resource.pyx:196:36: Invalid operand types for '|' (allocation_handle_type; allocation_handle_type)

I've anyway applied the change in 85a95de, but left the explicit cast in to make sure it compiles.

[vyasr]

I'm not sure what we're hoping to happen here.

• Switching to an enum class is a good thing to do in general for modern C++ usage, but if anything it makes the situation here worse because scoped enumerations are (by design) strongly typed and will not convert automatically to an integer even in C++ (here's a quick demo).
• One difference in binding C-style enums is that unlike in C they will not will not automatically convert to integers. You will have to cast yourself, as you found. Here's an example:

In [3]: %%cython
    ...: cdef enum A:
    ...:     x = 1
    ...:     y = 2
    ...:
    ...: cdef A a = A.x
    ...: cdef A b = A.y
    ...: cdef A c = a | b
    ...: print(c)
    ...:
    ...:

Error compiling Cython file:
------------------------------------------------------------
...
    x = 1
    y = 2

cdef A a = A.x
cdef A b = A.y
cdef A c = a | b
             ^
------------------------------------------------------------

/home/coder/.cache/ipython/cython/_cython_magic_698ab74b4727f04ebc23520f0c784e1a85498944.pyx:7:13: Cannot assign type 'int' to 'A'

• With a cpdef enum you get both a Python and a C enum (that's what the cpdef does). Because of how Python enums work, you will see this operator work in pure Python code because it uses the Python enum wrapper, but it will not work in typed Cython code. Compare

In [4]: %%cython --cplus
   ...: cpdef enum class A:
   ...:     x = 1
   ...:     y = 2
   ...:
   ...: a = A.x
   ...: b = A.y
   ...: c = a | b
   ...: print(c)
   ...:
   ...:
3

with

In [5]: %%cython --cplus
   ...: cpdef enum class A:
   ...:     x = 1
   ...:     y = 2
   ...:
   ...: cdef A a = A.x
   ...: cdef A b = A.y
   ...: cdef A c = a | b
   ...: print(c)
   ...:
   ...:

Error compiling Cython file:
------------------------------------------------------------
...
    x = 1
    y = 2

cdef A a = A.x
cdef A b = A.y
cdef A c = a | b
             ^
------------------------------------------------------------

/home/coder/.cache/ipython/cython/_cython_magic_b143dd57cf4b954689b33b6386f8a1098deb2571.pyx:7:13: Invalid operand types for '|' (A; A)

The "pure Python" usage above would work equally well if you had an enum instead of an enum class.