On Fri, Oct 13, 2006 at 03:50:46PM -0700, Damon Buckwalter <[EMAIL PROTECTED]> was heard to say: > Package: aptitude > Version: 0.4.3-1 > Severity: important > > > I've seen this problem repeatedly over time and found work of another > that describes the symptoms: > > http://lists.debian.org/debian-user/2006/07/msg00465.html > > To sum up, in the aptitude source at src/vscreen/vscreen.cc:779 > > // Block WINCH so the signal_thread can pick it up. > sigset_t signals; > sigemptyset(&signals); > sigaddset(&signals, SIGWINCH); > sigprocmask(SIG_BLOCK, &signals, NULL); > > This causes processes installed to inherit the signal mask. As > mentioned in the mailing list post linked above, the classic > manifestation of this in sshd and screen/mutt/top/etc. Installing a new > version of SSHd from aptitude leaves SIGWINCH blocked in the sshd > process, making terminal resizes ignored from within curses-type > applications. > > I am not an expert (nor have I found the code or time to work on a > patch), but conceptually it seems the per-thread sig mask needs to block > SIGWINCH for all threads except the one that handles it. I know that > there's got to be some weirdness in the process/thread mixed world. > > This is the article I'm basing my ideas on: > > http://www.linuxjournal.com/article/2121
Thanks for bringing this to my attention. This is rather surprising behavior, but I guess it's well-established. (annoyingly, the fork() manpage doesn't mention that signal masks are inherited; you need to read the libc manual to find this out) BTW, that article dates to 1997 and probably is only useful for general principles -- I'm pretty sure that Linux's threading architecture has been rewritten at least once since then. It looks like unblocking the signal in the thread that exec()s dpkg will work for now. I think an ideal option would be to reset the signal mask between fork() and exec(), but that would require cooperation from libapt, since I don't actually execute the dpkg sub-process myself. See also bug #214141. Daniel
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