Jesse Luehrs pointed out to be that man 7 signal has a list of functions that it’s safe to call from signal handlers. Signal handler, because they take locks internally. This means that a lot of convenientįunctions, including the stdio functions, malloc, etc., are unusable from a So, for instance, itĬan’t even wait on a lock, because the code that’s holding the lock is paused Interrupts and stops the original code from running.
Stronger than the restrictions on thread-safe code, since the signal handler This sets up some very onerous restrictions on whatĪ signal handler can do: it can’t assume that any locks are unlocked, anyĬomplex data structures are in a reliable state, etc. If you register a signal handler, it’s called in the middle of whatever code This paragraph from this article explains really wonderfully what is difficult about signal handlers: surprise! now you have a concurrent program! you need to be very careful if you modify anything in your signal handler code because WHO KNOWS what state that thing was in before you changed it.
#UNIX SIGNALS ITIMER HOW TO#
This is generally a normal thing that can happen but this weekend I saw a Rust program crash because it did not know how to handle EINTR. if you’re doing a read or write system call, and there’s a signal, your read might be interrupted! You will get a return value EINTR.you need to be careful and make sure that other signals do not arrive while you are handling a signal.the kernel will put your program back on its feet when it’s done with the signal! no problem! what can go wrong if you use signals? once my_awesome_function is done, it puts everything back and sends you on your way.It saves all the registers in your process, and runs my_awesome_function.the linux kernel is like “hey, a signal!”.You tell the Linux kernel signal(SIGALRM, my_awesome_function).
So! Let’s say you want to handle SIGALRM with my_awesome_function
#UNIX SIGNALS ITIMER INSTALL#
When you get sent SIGKILL nobody communicates with you, you just die immediately.īut the rest of the signals you’re allowed to install signal handlers for. Signals are a way for Unix processes to communicate! Except for SIGKILL. I was sort of surprised because I think of signals as being a little scary! Here are some facts I have collected to try to think through this. Yesterday I said I was scared of Unix signals, and some experienced people who I respect said “no, you should not be! unix signals are a very well known thing!”.
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