Is there a way to test whether I'm in a signal handler?

Question

I'm having to work on a logging module that can be called from various places in a large project. The problem I have is that sometimes the module may be called from code executed inside a signal handler. Normally, the logging module includes time data using localtime() and strftime(), but of course these calls are not async-signal safe, and can cause deadlocks if called from within a signal handler. Is there any way (on a GNU/Linux system) to tell whether or not my code is currently executing in a signal handler context, apart from e.g., having every signal handler set a flag while processing? I think it would be better to simplify our signal handlers, but in this case I don't have a choice as to where the logging module might be called. It would be nice if I could test and just omit the timestamp information if the module is called during signal handling.

Answer 1

Does your system have sigpending? I don't know what the behavior of that function is during a signal handler. If it returns a set flag, though, you could be pessimistic and skip async-unsafe calls if any signals are pending.