arc4random in a nutshell


No setup required

Callable in any context
    kernel
- most contexts
- from start of main(), maybe even during bootstrap

    userland:
- even inside chroot (filesystem agnostic)
- pthreads (self locking)
- libraries may safely call it (no setup required)
- even signal handlers

Always succeeds -- and returns a random result

Lack of failure condition means back-end code must be robust