This is a safe, deadlock-risk free way to monitor for arbitrary process exits. If/when that process disappears, you can then execute your code. The idea is you start up a child process, and in that child, observe the parent. I think you're only safe option is to use a sentinel process. This may not matter to do, depending on how strong a guarantee you need about detecting your process termination. Third, there are fatal events that aren't mapped to signals, on top of SIGKILL. And, those deadlocks will occur during unpredictable points of its execution.

In short: it is almost certainly unsafe to run your code in a signal handler, and it will deadlock sometimes. However, since it can be delivered at any time, it still will be subject to async safety issues, even thought it is not a crash. Now, I will admit that my experience with signals does not include use of SIGTERM. But, will also sometimes deadlock, depending on what the thread was doing at the time. Calling unsafe functions, like NSLog, will sometimes work. If you check out 'man sigaction' (note, sigaction is a much improved API over signal) you see that there are actually a very small number of functions that are safe to call from a signal handler. This is an part of a class of problems known as 'async safety'. Examples of things that hold locks - malloc/free, the Objective-C runtime. Second, signals interrupt a thread, and that thread can be doing anything, including holding locks. There are other, legitimate uses of signals, and installing handlers will negatively impact their behavior without very careful work. Unfortunately, there are, in fact, some major issues with the suggested approach.įirst, signal handlers are per-process.

Major credit goes to for putting work in here to come up with an answer.

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