System Calls

Linux 04 Sep 2026 9 min read

Handle Linux Signals in Event Loops with signalfd

Unix signals are asynchronous by design: a signal can interrupt a program between ordinary instructions and transfer control to a signal handler. That model is useful, but it creates an awkward boundary for event-driven programs. A network server may already spend most of its time inside poll(), epoll_wait(), or another readiness API. Its sockets, pipes, and timers appear as file-descriptor events, while SIGTERM and SIGHUP arrive through a separate execution path with much stricter rules about what code may safely run.

Linux Signals

Linux 04 Sep 2026 8 min read

Avoid PID Reuse Races on Linux with pidfds

A process ID looks like an identity, but it is really a reusable number. That distinction matters in long-running supervisors, job managers, test harnesses, and other programs that observe a process and then act on it later. Between those two operations, the original process can exit and Linux can eventually reuse the same PID for an unrelated process. Traditional PID-based code can therefore have a time-of-check/time-of-use race: check PID 4242 -> original process exits -> PID 4242 is reused -> signal PID 4242 Linux PID file descriptors, usually called pidfds, provide another model. Instead of repeatedly identifying a task by a reusable integer, a program obtains a file descriptor that refers to a particular process and can use that descriptor with pidfd-aware APIs.

Linux Processes