[cyphar]

Signal sending cannot block, so you'd need to have an unlimited amount of memory in order to guarantee that all signals are delivered. Not to mention that some signals allow you to block a process in the middle of a syscall (resulting in the lovely restart_syscall and EINTR hacks).

Also, signalfd(2) has its own lovely host of problems (caused by the fact that a file descriptor and signals don't match in abstractions). On fork(), sendmsg() or exec() or any other interesting event, the file descriptor starts to lean towards breaking POSIX. In addition, because of signals' interactions with threads, you get some even odder interactions when you read from the fd in a multithreaded program (they share the file descriptor table but will read different data).