def one_norm(in_buf, inout_buf, datatype):
# This mapping MPI datatype -> NumPy dtype
# only works for built-in MPI datatypes
typecode = MPI._typecode(datatype)
assert typecode is not None # check MPI datatype is built-in
dtype = np.dtype(typecode)
# `in_buf`, `inout_buf` are buffer-like objects exposing raw bytes
# don't use them directly but convert them to numpy arrays
in_array = np.frombuffer(in_buf, dtype) # `in_array` and `in_buf` share memory
inout_array = np.frombuffer(inout_buf, dtype) # `inout_array` and `inout_buf` share memory
def fn_sum(buffer_a, buffer_b, t):
tc = MPI._typecode(t) # map MPI datatype -> Python typecode
array_a = np.frombuffer(buffer_a, dtype=tc)
array_b = np.frombuffer(buffer_b, dtype=tc)
array_b += array_a
