BUG: DLPack cannot export readonly buffers and raises wrong exception #20742
Description
Describe the issue:
The root issue is currently DLPack does not support exporting readonly arrays:
numpy/numpy/core/src/multiarray/dlpack.c
Lines 122 to 126 in 7262b9c
which prevents its usefulness from situations where downstream consumers only need to read it or wrap it in the same readonly fashion (ex: JAX, MPI). IMHO NumPy should not make this abrupt decision for consumers, but instead just raises a warning.
But, for short-term solution before we converge, it's more important that a BufferError, instead of TypeError, is raised, in order to be aligned with the Python buffer protocol. In mpi4py, we do not anticipate TypeError and it causes this test to fail in our CI, which is a regression:
https://github.com/mpi4py/mpi4py/blob/02a6f31f6cc4a5779c6414b993a714caa2bf93c6/test/test_msgspec.py#L399-L404
Reproduce the code example:
import numpy as np
a = np.arange(10)
a.flags.writeable = False
b = np._from_dlpack(a)Error message:
https://github.com/mpi4py/mpi4py-testing/runs/4676901782?check_suite_focus=true
======================================================================
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ERROR: testNotWriteable (test_msgspec.TestMessageSimpleNumPy)
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----------------------------------------------------------------------
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Traceback (most recent call last):
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File "mpi4py/MPI/asbuffer.pxi", line 60, in mpi4py.MPI.PyMPI_GetBuffer
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ValueError: buffer source array is read-only
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During handling of the above exception, another exception occurred:
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Traceback (most recent call last):
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File "/home/runner/work/mpi4py-testing/mpi4py-testing/mpi4py/test/test_msgspec.py", line 403, in testNotWriteable
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self.assertRaises((BufferError, ValueError),
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File "/opt/hosted
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toolcache/Python/3.9.9/x64/lib/python3.9/unittest/case.py", line 739, in assertRaises
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return context.handle('assertRaises', args, kwargs)
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File "/opt/hostedtoolcache/Python/3.9.9/x64/lib/python3.9/unittest/case.py", line 201, in handle
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callable_obj(*args, **kwargs)
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File "/home/runner/work/mpi4py-testing/mpi4py-testing/mpi4py/test/test_msgspec.py", line 133, in Sendrecv
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MPI.COMM_SELF.Sendrecv(sendbuf=smsg, dest=0, sendtag=0,
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File "mpi4py/MPI/Comm.pyx", line 328, in mpi4py.MPI.Comm.Sendrecv
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File "mpi4py/MPI/msgbuffer.pxi", line 447, in mpi4py.MPI.message_p2p_recv
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File "mpi4py/MPI/msgbuffer.pxi", line 433, in mpi4py.MPI._p_msg_p2p.for_recv
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File "mpi4py/MPI/Comm.pyx", line 199, in mpi4py.MPI.Comm.Split
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File "mpi4py/MPI/msgbuffer.pxi", line 138, in mpi4py.MPI.message_basic
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File "mpi4py/MPI/asbuffer.pxi", line 264, in mpi4py.MPI.getbuffer
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File "mpi4py/MPI/asbuffer.pxi", line 64, in mpi4py.MPI.PyMPI_GetBuffer
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File "mpi4py/MPI/asbuffer.pxi", line 62, in mpi4py.MPI.PyMPI_GetBuffer
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File "mpi4py/MPI/asdlpack.pxi", line 193, in mpi4py.MPI.Py_GetDLPackBuffer
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TypeError: NumPy currently only supports dlpack for writeable arraysNumPy/Python version information:
NumPy 1.22.0