Does UCC expose point-to-point communication API?

[MaoZiming]

It seems UCC implements software collectives using point-to-point communication libraries such as UCX. Does / Can UCC expose API for both collective communication and point-to-point communication? Are there potential challenges in doing so?
Thank you!

[Sergei-Lebedev]

UCC does not expose an API for point-to-point communication. Instead, it is recommended to use UCX for this purpose. However, there is a workaround that allows for point-to-point communication using broadcast within an active set of size 2. This technique is utilized in PyTorch’s process group for send/recv operations.

https://github.com/pytorch/pytorch/blob/7b074346e0a3e97da43f9c7f5c84f39e7b7184e6/torch/csrc/distributed/c10d/ProcessGroupUCC.cpp#L1577

https://github.com/pytorch/pytorch/blob/7b074346e0a3e97da43f9c7f5c84f39e7b7184e6/torch/csrc/distributed/c10d/ProcessGroupUCC.cpp#L1614