From: David Laight > Sent: 12 June 2019 15:18 > From: Oleg Nesterov > > Sent: 12 June 2019 14:46 > > On 06/11, David Laight wrote: > > > > > > If I have an application that has a loop with a pselect call that > > > enables SIGINT (without a handler) and, for whatever reason, > > > one of the fd is always 'ready' then I'd expect a SIGINT > > > (from ^C) to terminate the program. > > > > This was never true. > > > > Before Eric's patches SIGINT can kill a process or not, depending on timing. > > In particular, if SIGINT was already pending before pselect() and it finds > > an already ready fd, the program won't terminate. > > Which matches what I see on a very old Linux system. > > > After the Eric's patches SIGINT will only kill the program if pselect() does > > not find a ready fd. > > > > And this is much more consistent. Now we can simply say that the signal will > > be delivered only if pselect() fails and returns -EINTR. If it doesn't have > > a handler the process will be killed, otherwise the handler will be called. > > But is it what the standards mandate? > Can anyone check how Solaris and any of the BSDs behave? > I don't have access to any solaris systems (I doubt I'll get the disk to > spin on the one in my garage). > I can check NetBSD when I get home. I tested NetBSD last night. pselect() always calls the signal handlers even when an fd is ready. I'm beginning to suspect that this is the 'standards conforming' behaviour. I don't remember when pselect() was added to the ToG specs, it didn't go through XNET while I was going to the meetings. David > > The ToG page for pselect() http://pubs.opengroup.org/onlinepubs/9699919799/functions/pselect.html > says: > "If sigmask is not a null pointer, then the pselect() function shall replace > the signal mask of the caller by the set of signals pointed to by sigmask > before examining the descriptors, and shall restore the signal mask of the > calling thread before returning." > Note that it says 'before examining the descriptors' not 'before blocking'. > Under the general description about signals it also says that the signal handler > will be called (or other action happen) when a pending signal is unblocked. > So unblocking SIGINT (set to SIG_DFL) prior to examining the descriptors > should be enough to cause the process to exit. > The fact that signal handlers are not called until 'return to user' > is really an implementation choice - but (IMHO) it should appear as if they > were called at the time they became unmasked. > > If nothing else the man pages need a note about the standards and portability. > > David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
