The Expert module contains functions that novice users should avoid, due to their
complexity.
An OCaml signal handler can run at any time, which introduces all the semantic
complexities of multithreading. It is much easier to use Async's signal handling, see
Async_unix.Signal, which does not involve multithreading, and runs user code as
ordinary Async jobs. Also, beware that there can only be a single OCaml signal
handler for any signal, so handling a signal with a Core signal handler will
interfere if Async is attempting to handle the same signal.
All signal handler functions are called with Exn.handle_uncaught_and_exit, to
prevent the signal handler from raising, because raising from a signal handler could
raise to any allocation or GC point in any thread, which would be impossible to
reason about.
If you do use Core signal handlers, you should strive to make the signal handler
perform a simple idempotent action, like setting a ref.