Notice how long and complex your discussion of this issue is, and how many different systems you have to investigate in depth to even begin to form a coherent picture.

All we're trying to do is close a file safely. This is core functionality that virtually every application will have to depend on. It would be like free() saying it might be interrupted by a signal, and you have no way of knowing if the memory has actually been deallocated or not. That would be insane.