The simplest way to write safe signal handlers is to only ever:
- write(2) to STDERR_FILENO
- write(2) to a "self-pipe" (i.e., a pipe where the same
process is waiting on in its event loop), thus turning
the async signal event into an async *I/O* event that
can be handled without any constraints regarding
async-signal-safety
- _exit()
Yes, there are other async-signal-safe functions that can be called from a signal handler, but it's generally not worth it. Adhering to my more constrained approach will keep your code safe and will make it easier to always get it right.
ALSO, while we're at it, the only global or thread-local variables you can read from or write to from a signal handler must be of type volatile sig_atomic_t (or else volatile of any other integral or pointer type that you can use with atomic operations). This is very important. E.g., imagine using SIGUSR1/2 to manage verbosity levels...
ALSO, while we're at it, the only global or thread-local variables you can read from or write to from a signal handler must be of type volatile sig_atomic_t (or else volatile of any other integral or pointer type that you can use with atomic operations). This is very important. E.g., imagine using SIGUSR1/2 to manage verbosity levels...