> In general, file systems make for poor IPC implementations.

I agree but also they do have advantages such as simplicity, not needing to explicitly declare which files are needed, lazy data transfer, etc.

> you'll also want some mechanism for the writer to notify the reader that it's finished, be it with file locks, or some other entirely different protocol to send signals over the network.

The writer is always finished before the reader starts in these scenarios. The issue is reads on one machine aren't guaranteed to be ordered after writes on a different machine due to write caching.

It's exactly the same problem as trying to do multithreaded code. Thread A writes a value, thread B reads it. But even if they happen sequentially in real time thread B can still read an old value unless you have an explicit fence.