Cygwin developers, I'm worried about a Cygwin bug where pthread_kill may not send a signal to the correct thread. This bug may be causing Emacs to crash. The Cygwin bug is discussed in this thread:
http://cygwin.com/ml/cygwin/2012-05/msg00472.html Emacs uses pthread_kill to redirect SIGCHLD to the main thread; if this is sent to a random thread instead, that could explain the random crashes. My question is: does this bug still exist with Cygwin, and if so is it likely to get fixed soon? More details about the Emacs bug can be found here: http://bugs.gnu.org/14569 Briefly, Emacs is crashing randomly on Cygwin ever since it started doing this: /* Tickle glib's child-handling code. Ask glib to wait for Emacs itself; this should always fail, but is enough to initialize glib's private SIGCHLD handler. */ g_source_unref (g_child_watch_source_new (getpid ())); After this newly-inserted code, Emacs finds out what the child signal handler was: /* Now, find out what glib's signal handler was, and store it into lib_child_handler. */ struct sigaction action, old_action; emacs_sigaction_init (&action, deliver_child_signal); sigaction (SIGCHLD, &action, &old_action); eassert (! (old_action.sa_flags & SA_SIGINFO)); if (old_action.sa_handler != SIG_DFL && old_action.sa_handler != SIG_IGN && old_action.sa_handler != deliver_child_signal) lib_child_handler = old_action.sa_handler; Emacs's SIGCHILD handler, deliver_child_signal, arranges the signal handling to occur in the main thread (to avoid races within Emacs), like this: int old_errno = errno; bool on_main_thread = true; if (! pthread_equal (pthread_self (), main_thread)) { sigset_t blocked; sigemptyset (&blocked); sigaddset (&blocked, sig); pthread_sigmask (SIG_BLOCK, &blocked, 0); pthread_kill (main_thread, sig); on_main_thread = false; } if (on_main_thread) handle_child_signal (sig); errno = old_errno; And handle_child_signal, which runs in the main thread, does a bunch of Emacsish things and then invokes lib_child_handler (sig), which is glib's SIGCHLD handler. All this works just fine on Fedora and other platforms; but it doesn't work on Cygwin. -- 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
