On Sat, Sep 19, 2009 at 10:31:58AM +0000, Waldemar Rachwal wrote: >On Fri, Sep 18, 2009 at 04:57:56PM +0000, Waldemar Rachwal wrote: >>Apparently, signals like SIGWINCH and SIGCHLD, which are a little bit >>special, need to be kicked by other signal to be eventually returned by >>sigwait(). >> >Christopher Faylor <cgf-use-the-mailinglist-please <at> cygwin.com> writes: >>Thanks for the test case. The problem has nothing to do with anything >>"special" about SIGCHLD. It's a signal like any other signal. > >I am not sure it's clear. With regard to sigwait() SIGCHLD like any >other signal must not only be blocked, additionally like any other >signal it cannot be ignored, which is not common as only few signals >are ignored by default, and SIGCHLD and SIGWINCH are in this group.
I was explaining the problem to you. As I said, SIGCHLD is a signal like any other signal and if you had tried to use a similar mechanism to trap, say, SIGINT, you would have seen the same problem. >POSIX is explicit here: > >http://www.opengroup.org/onlinepubs/9699919799/ > ><quote> >2.4.1 Signal Generation and Delivery > >However, a signal can be "blocked" from delivery to a thread. > >If the action associated with a blocked signal is anything other than to >ignore the signal, and if that signal is generated for the thread, > >the signal shall remain pending until > >it is unblocked, > >it is accepted when it is selected and returned by a call to the >sigwait() function, > >or the action associated with it is set to ignore the signal. ></quote> > >Simply a signal must be blocked and (actually) not ignored to be >processed by sigwait(). > >> Cygwin was not performing sigwait() processing if there was a handler >> set up for the signal. Your test case would have worked if you had not >> set up a dummy handler. > >As stated above a handler is the must, otherwise the test won't work >under POSIX systems. Since the "above" never mentioned the word handler, I don't see how your point is valid. blocked != handler. blocked == sigprocmask or some similar mechanism. You did use sigprocmask in your example. Setting the handler doesn't seem to serve any useful purpose since it isn't being used. I tested this on linux just to be sure. Actually, on some versions of linux you don't even have to block the signal first. In any event, you provided a test case, I provided a fix. That's the desired outcome. Arguing about this is pointless unless the fix didn't actually fix anything. cgf -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
