I have a deeper set of followup changes I am working on for a post-4.3 release that rewrite the signal handling in GNU make, so that we do not do any work in signal handlers other than setting flags. Today, far too much is done in signal handlers resulting in a number of bugs about hangs etc. (and I've even seen this happen myself in my systems).
Of course the trick to this is that we have to be regularly checking those flags since we are no longer relying on asynchronous signal handlers, and unfortunately GNU make doesn't really have one centralized event loop where this can be done. What I'm considering is enhancing the EINTRLOOP etc. macros that I have added across the code to check all system calls for EINTR and restart them, so that this macro also checks to see if a signal has been received and if so, calls a handler function. For almost all signals this is just die() although of course for SIGCHLD we need something different. This seems like a straightforward way to quickly detect signals without a lot of code churn. I have a simple implementation of this which passes all the unit tests, but I know for sure that there are race conditions (where if children die at certain times we won't detect it) so more thought needs to be applied here. Unfortunately we again find ourselves faced with the frustration of handling signals and waiting on file descriptors at the same time, that we've struggled with ever since the jobserver was implemented, *sigh*.
