On Mon, Aug 14, 2017 at 08:03:07AM +0200, Houder wrote: > On Fri, 4 Aug 2017 00:44:45, Noah Misch wrote: > > The attached demonstration program blocks signals (with sigprocmask()) to > > achieve mutual exclusion between signal handlers. It aborts upon receipt > > of a > > blocked signal. On "CYGWIN_NT-10.0 2.7.0(0.306/5/3) 2017-02-12 13:18 > > x86_64", > > signals regularly arrive despite being blocked. Essential parts of the > > program include handling two signal numbers and having handlers run for at > > least 1-2ms; this problem goes away if I remove one of those attributes. > > GNU/Linux, AIX, Solaris, and "CYGWIN_NT-6.0 1.7.27(0.271/5/3) 2013-12-09 > > 11:57 > > i686" never deliver a blocked signal to this program. I think this Cygwin > > behavior is non-conforming.
> I do not think that Cygwin is the problem here; your code is the problem > here, I believe. > > Please, study, for example, chapters 20 and 21 of LPI (Linux Programming > Interface by Michael Kerrisk). > > (20.10 The Signal Mask (Blocking Signal Delivery) > (20.13 Changing Signal Dispositions: sigaction()) > > You cannot use sigprocmask() like you do; you cannot use SIG_SETMASK as > a parameter in sigprocmask() within the context of a handler. What words in those chapters prompted your conclusion? I see nothing in 20.10 or 20.13 about contextual restrictions on SIG_SETMASK. Posix mentions no such restrictions in its sigprocmask() page, and Posix does say: The following table defines a set of functions that shall be async-signal-safe. Therefore, applications can call them, without restriction, from signal-catching functions. ... sigprocmask() -- http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html > Cygwin exhibits misbehaviour in case of your code, because it is slower > than Linux; however, the code is also wrong for Linux. > > The misbehaviour occurs as result of nested interrupts in case of your > code (yes, nested interrupts are possible with Linux/Unix!). > However your code does not experience nesting under Linux, because, as > I said, Linux is faster than Cygwin. My code *does* experience signal handler nesting on Linux. In fact, handlers nest far more quickly than they do under Cygwin. However, all its nesting under Linux takes place outside the sigprocmask()-bounded critical section. The algorithm that inspired this test case tolerates that nesting, but it does not tolerate nesting within the critical section. > The simplest way to exclude one signal from another, is to specify the > signal (or signals) in the sa_mask of the sigaction parameter ... That is true. However, as you discovered in your other thread, it is not an effective workaround for $SUBJECT. nm -- 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
