Fix sharing of empty tensor in multiprocessing #6229
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Fixes pytorch#5719 Previously, the following would error out with an "Invalid file descriptor" error: ``` import torch import torch.multiprocessing as mp q = mp.Queue() t = torch.tensor([]) q.put(t) ``` on some OSes. The problem was that because one cannot mmap data of size 0, and that an empty tensor has a storage of size 0, the file descriptor for the storage (referencing shared memory) was not being set. The multiprocessing sharing code then calls DupFD on that uninitialized file descriptor, leading to an error. This PR special cases sharing an empty tensor on the CPU. CUDA does not have this problem. Unit tests for both cpu and cuda empty tensors
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colesbury
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Fixes #5719
Previously, the following would error out with an "Invalid file
descriptor" error:
on some OSes. The problem was that because one cannot mmap data of size
0, and that an empty tensor has a storage of size 0, the file descriptor
for the storage (referencing shared memory) was not being set. The
multiprocessing sharing code then calls DupFD on that uninitialized file
descriptor, leading to an error.
This PR special cases sharing an empty tensor on the CPU. CUDA does not
have this problem.
cc @colesbury
Test Plan
Unit tests for both cpu and cuda empty tensors