Re: open-network-stream to dead host hang XEmacs

Simon Josefsson <simon(a)josefsson.org&gt; writes: > $ xemacs -vanilla > (open-network-stream "bug" nil "10.0.0.42" 42) > > Now XEmacs 21.1 (and 20.4) is hung, C-g doesn't do anything. XEmacs > 21.2 seem fine. Perhaps the solution used there could be back-ported > to XEmacs 21.1? I am afraid there are two bugs here. The first one is fundamental and causes C-g in X not to work for interrupting system calls and the second one makes it work in 21.2 nevertheless. Alas I only understand and can "fix" the latter :-( Some explanations follow. (warning: I looked at most of this code for the first time and don't understand some of it): - before calling connect() we call slow_down_interrupts() (for rather unclear reasons documented in the slightly strange comments). - slow_down_interrupts ends up calling unrequest_sigio_on_device() for the X file descriptor. In 21.2 this contains ------------ #if defined (I_SETSIG) && !defined(HPUX10) { int events=0; ioctl (filedesc, I_GETSIG, &events); ioctl (filedesc, I_SETSIG, events & ~S_INPUT); } #elif defined (FASYNC) fcntl (filedesc, F_SETFL, fcntl (filedesc, F_GETFL, 0) & ~FASYNC); ------------- On Linux with glibc2.1 I_SETSIG is defined but the ioctl don't actually work (this seems to be a feature), strace shows: 14:36:07 ioctl(6, CDROMVOLCTRL, 0xbfffea84) = -1 EINVAL (Invalid argument) <0.000010> 14:36:07 ioctl(6, CDROMEJECT, 0) = -1 EINVAL (Invalid argument) <0.000008> The effect is that SIGIO is *not* disabled and C-g is detected and works as normal. For 21.1 Jan applied a patch to the above http://www.xemacs.org/list-archives/xemacs-patches/199906/msg00000.html -#if defined (I_SETSIG) && !defined(HPUX10) +#if defined (I_SETSIG) && !defined(HPUX10) && !defined(LINUX) now the fcntl () is executed instead and this works, i.e. SIGIO is disabled and we rely on the slowed down C-g detection to work. Only problem is it doesn't... After 15 seconds the expected SIGALARM arrives and the X event queue is inspected for C-g but for some reason the C-g is not found. In my debugging run the C-g event was just not there. Another problem is that the SIGALARM is generated only once (this is fixable I guess). If I generate another couple of SIGALARMs by hand with kill then the C-g eventually shows up in the queue and open-network-stream is quit.