From the question:
Is it good programming practice to use setjmp and longjmp in C?
Two of the comments left said:
"You can't throw an exception in a signal handler, but you can do a longjmp safely -- as long as you know what you are doing. – Dietrich Epp Aug 31 at 19:57 @Dietrich: +1 to your comment. This is a little-known and completely-under-appreciated fact. There are a number of problems that cannot be solved (nasty race conditions) without using longjmp out of signal handlers. Asynchronous interruption of blocking syscalls is the classic example."
I was under the impression that signal handlers were called by the kernel when it encountered an exceptional condition (e.g. divide by 0). Also, that they're only called if you specifically register them.
This would seem to imply (to me) that they aren't called through your normal code.
Moving on with that thought... setjmp and longjmp as I understand them are for collapsing up the stack to a previous point and state. I don't understand how you can collapse up a stack when a signal handler is called since its called from the Kernel as a one-off circumstance rather than from your own code. What's the next thing up the stack from a signal handler!?
longjmp does not perform normal stack unwinding. Instead, the stack pointer is simply restored from the context saved by setjmp.
Here is an illustration on how this can bite you with non-async-safe critical parts in your code. It is advisable to e.g. mask the offending signal during critical code.