Fix race condition on shutdown

This commit fixes primarily a race condition that occurs when xinit(1) shuts
down: by not acting properly fluxbox gets caught in an infinite loop. It
caused bug #1100.

xinit(1) sends a SIGHUP signal to all processes. fluxbox tries to shutdown
itself properly by shutting down workspaces and screens. While doing that, the
Xserver might be gone already. Additionally, fluxbox used to restart() itself
on SIGHUP, which is clearly not the right thing to do when xinit(1) is about
to end the session.

So, fluxbox does this:

* handling SIGHUP now shuts down fluxbox without clearing workspaces and
  screens.

* A 2 second alarm() is triggered in Fluxbox::shutdown() as a last resort

* XSetIOErrorHandler() is used to recognize the disconnect from the xserver.

* SIGUSR1 is for restarting fluxbox, SIGUSR2 for reloading the config

* FbTk/SignalHandler.cc/hh is gone; this unused abstraction served currently
  no real purpose. Signal handling is now done in main.cc

* Unrelated to the issue itself src/main.cc was trimmed down quite a bit and
  the code (responsible for handling the command line interface) was moved to
  src/cli*

1 files changed, 24 insertions, 73 deletions

diff --git a/src/fluxbox.cc b/src/fluxbox.cc
index 8305b8a..07419ba 100644
--- a/src/fluxbox.cc
+++ b/src/fluxbox.cc
@@ -177,11 +177,15 @@ int handleXErrors(Display *d, XErrorEvent *e) {
 //            kill(0, 2);
     }
 #endif // !DEBUG
-
     return False;
 }
 
 
+int handleXIOErrors(Display* d) {
+    cerr << "Fluxbox: XIOError: lost connection to display.\n";
+    exit(1);
+}
+
 
 /* functor to call a memberfunction with by a reference argument
    other places needs this helper as well it should be moved
@@ -290,21 +294,8 @@ Fluxbox::Fluxbox(int argc, char **argv,
     s_kwm2_dockwindow = XInternAtom(disp,
                                     "_KDE_NET_WM_SYSTEM_TRAY_WINDOW_FOR", False);
     // setup X error handler
-    XSetErrorHandler((XErrorHandler) handleXErrors);
-
-    //catch system signals
-    SignalHandler &sigh = SignalHandler::instance();
-    sigh.registerHandler(SIGSEGV, this);
-    sigh.registerHandler(SIGFPE, this);
-    sigh.registerHandler(SIGTERM, this);
-    sigh.registerHandler(SIGINT, this);
-#ifndef _WIN32
-    sigh.registerHandler(SIGPIPE, this); // e.g. output sent to grep
-    sigh.registerHandler(SIGCHLD, this);
-    sigh.registerHandler(SIGHUP, this);
-    sigh.registerHandler(SIGUSR1, this);
-    sigh.registerHandler(SIGUSR2, this);
-#endif
+    XSetErrorHandler(handleXErrors);
+    XSetIOErrorHandler(handleXIOErrors);
 
     //
     // setup timer
@@ -896,58 +887,6 @@ void Fluxbox::handleClientMessage(XClientMessageEvent &ce) {
     }
 }
 
-/// handle system signals
-void Fluxbox::handleSignal(int signum) {
-    _FB_USES_NLS;
-
-    static int re_enter = 0;
-
-    switch (signum) {
-#ifndef _WIN32
-    case SIGCHLD: // we don't want the child process to kill us
-        // more than one process may have terminated
-        while (waitpid(-1, 0, WNOHANG | WUNTRACED) > 0);
-        break;
-    case SIGHUP:
-        restart();
-        break;
-    case SIGUSR1:
-        load_rc();
-        break;
-    case SIGUSR2:
-        reconfigure();
-        break;
-#endif
-    case SIGSEGV:
-        abort();
-        break;
-    case SIGFPE:
-    case SIGINT:
-#ifndef _WIN32
-    case SIGPIPE:
-#endif
-    case SIGTERM:
-        shutdown();
-        break;
-    default:
-        fprintf(stderr,
-                _FB_CONSOLETEXT(BaseDisplay, SignalCaught, "%s:      signal %d caught\n", "signal catch debug message. Include %s for Command<void> and %d for signal number").c_str(),
-                m_argv[0], signum);
-
-        if (! m_starting && ! re_enter) {
-            re_enter = 1;
-            cerr<<_FB_CONSOLETEXT(BaseDisplay, ShuttingDown, "Shutting Down\n", "Quitting because of signal, end with newline");
-            shutdown();
-        }
-
-
-        cerr<<_FB_CONSOLETEXT(BaseDisplay, Aborting, "Aborting... dumping core\n", "Aboring and dumping core, end with newline");
-        abort();
-        break;
-    }
-}
-
-
 void Fluxbox::windowDied(Focusable &focusable) {
     FluxboxWindow *fbwin = focusable.fbwindow();
 
@@ -1122,18 +1061,30 @@ void Fluxbox::restart(const char *prog) {
     }
 }
 
-/// prepares fluxbox for a shutdown
-void Fluxbox::shutdown() {
+// prepares fluxbox for a shutdown. when x_wants_down is != 0 we assume that
+// the xserver is about to shutdown or is in the midst of shutting down
+// already. trying to cleanup over a shaky xserver connection is pointless and
+// might lead to hangups.
+void Fluxbox::shutdown(int x_wants_down) {
     if (m_shutdown)
         return;
 
+    Display *dpy = FbTk::App::instance()->display();
     m_shutdown = true;
 
-    XSetInputFocus(FbTk::App::instance()->display(), PointerRoot, None, CurrentTime);
+#ifdef HAVE_ALARM
+    // give ourself 2 seconds (randomly picked randon number) to shutdown
+    // and then try to reenter signal handling. a bad race condition might
+    // lead to an inifite loop and this is some kind of last resort
+    alarm(2);
+#endif
 
-    STLUtil::forAll(m_screen_list, mem_fun(&BScreen::shutdown));
+    XSetInputFocus(dpy, PointerRoot, None, CurrentTime);
 
-    sync(false);
+    if (x_wants_down == 0) {
+        STLUtil::forAll(m_screen_list, mem_fun(&BScreen::shutdown));
+        sync(false);
+    }
 }
 
 /// saves resources