On Wed, Aug 30, 2017 at 02:06:02PM -0700, Brandon Williams wrote: > > We could extend that protection by having sigchain_push_common() set > > sa_mask to cover all of the related signals. On Linux and BSD the > > current code using signal() also implies SA_RESTART. We could add that > > to our flags, though I suspect in practice it doesn't matter. Whenever > > we establish a handler like this our intent is to never return from it. > > > > That just protects us from calling the _same_ handler from itself. But > > that's probably enough in practice, and means handlers don't have to > > worry about "critical sections". The other alternative is sigprocmask() > > to block signals entirely during a section. I'm not sure if there are > > portability questions there (it looks like we have a mingw wrapper > > there, but it's a complete noop). > > Yeah there's a lot about signals that I'm not very clear on. I do know > that Eric helped me out on the fork-exec series I worked on earlier in > the year and I believe it was to turn on/off signals during process > launches in 45afb1ca9 (run-command: block signals between fork and > execve, 2017-04-19). Though that bit of code is strictly for unix so I > wouldn't know how that would work on windows machines. Portability does > seem to always be a challenging problem. Based on the sketch I wrote above, I figured it would be pretty easy to convert sigchain to sigaction. But after taking a look at compat/mingw.c, I don't think Windows would be on board. sigaction() there is is a stub implementation that _only_ handles SIGALRM and nothing else. So I think the best we could do is put big #ifdefs around it to use sigaction on other platforms, and fall back to signal() on Windows. That's do-able, but my enthusiasm is waning as the complexity increases. Getting two SIGINTs in a row seems plausible, but we already handle that well. Getting SIGINT and then a _different_ signal while we're in the handler seems less likely in practice. The only combination I can think that would be common is TERM+KILL, but of course we're not catching KILL in the first place. So this seems like adding complexity for very little benefit. -Peff
