Signalfd can mostly be implemented on any platform using a pipe (if you don't have to mix 32-bit and 64-bit processes, or if you don't need the siginfo payload, or if you read your kernel's documentation enough to figure out which "layout" of the union members is active - this is really hairy). Note however the major caveat of running out of pipe buffer.

A more-reliable alternative is to use an async-signal-safe allocator (e.g. an `mmap` wrapper) to atomically store the payloads, and only use a pipe as a flag for whether there's something to look for.

Of course, none of these mechanisms are useful for naturally synchronous signals, such as the `SIGSEGV` from dereferencing an invalid pointer, so the function-coloring approach still needs to be used.

Every 'nix can do that. Your signal handler just writes a byte to a pipe and your main loop reads the pipe or fifo. The pipe/fifo is your event queue, which your main loop reads.

Seems kinda limiting.

If I've got a slow file download going on in one thread, and my program gets a Ctrl+C signal, waiting for the download to complete before I exit ain't exactly a great user experience.