[Question] Is there undefined behavior between the calls to `cudaFree` and `cudaIpcCloseMemHandle`?

In `Buffer::destroy`, each rank first closes the 7 external memory handles, then `cudaFree`s the local buffer.

However, the docs for `cudaIpcOpenMemHandle` says it is undefined behavior to `cudaFree` the *exported memory region* before the call to `cudaIpcCloseMemHandle`.

So in an extreme situation (actually I think this may be common) it is possible for rank 2 to close the handle exported from rank 1 long after rank 1 has freed that buffer. This should be technically considered undefined behavior, although I haven't been able to construct a test that exhibits clearly erroneous behavior, e. g. crashes.

Basically I am wondering about the robustness of this code: is it UB? Does it just happen to work? Or it is guaranteed to work given the current CUDA implementations?