If you have accessibility enabled, and run emacs, then metacity sometimes gets stuck while processing a11y events. To reproduce: 1. Make sure a11y is enabled in System->Preferences->Assistive Technologies 2. Open a terminal 3. Type: emacs -q --eval '(blink-cursor-mode 0)' & 4. Switch to the emacs window if it didn't get focused already 5. Type Alt-Tab to switch away from the emacs window Metacity hangs, like so: #0 0x0039f424 in __kernel_vsyscall () #1 0x0109b8cb in __poll (fds=0x113fff4, nfds=6, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:83 #2 0x00a6b8cc in IA__g_poll (fds=0x8ea5240, nfds=6, timeout=-1) at gpoll.c:127 #3 0x00a5e813 in g_main_context_poll (n_fds=<value optimized out>, fds=<value optimized out>, priority=<value optimized out>, timeout=<value optimized out>, context=<value optimized out>) at gmain.c:2904 #4 g_main_context_iterate (n_fds=<value optimized out>, fds=<value optimized out>, priority=<value optimized out>, timeout=<value optimized out>, context=<value optimized out>) at gmain.c:2586 #5 0x00a5eb04 in IA__g_main_context_iteration (context=0x8e7cd00, may_block=1) at gmain.c:2654 #6 0x00c3caa8 in link_main_iteration (block_for_reply=1) at linc.c:285 #7 0x00c1ec14 in giop_recv_buffer_get (ent=0xbfe900d0, timeout=0xbfe900e8) at giop-recv-buffer.c:727 #8 0x00c23bbc in ORBit_small_invoke_stub (obj=0x8e8f5c0, m_data=0x6046b00, ret=0x0, args=0xbfe901ec, ctx=0x0, ev=0xc65dcc) at orbit-small.c:660 #9 0x00c23de6 in ORBit_small_invoke_stub_n (object=0x8e8f5c0, methods=0xffffffff, index=0, ret=0x0, args=0xbfe901ec, ctx=0x0, ev=0xc65dcc) at orbit-small.c:577 #10 0x00c3094c in ORBit_c_stub_invoke (obj=0x8e8f5c0, methods=0x6046c44, method_index=0, ret=0x0, args=0xbfe901ec, ctx=0x0, ev=0xc65dcc, class_id=0, method_offset=4, skel_impl=0x6024400 <_ORBIT_skel_small_Accessibility_EventListener_notifyEvent>) at poa.c:2649 #11 0x060147d5 in Accessibility_EventListener_notifyEvent (_obj=0x8e8f5c0, e=0xbfe90224, ev=0xc65dcc) at Accessibility-stubs.c:422 #12 0x00c61dcc in spi_atk_emit_eventv (gobject=0x8e7a570, detail1=0, detail2=0, any=0xbfe902b0, format=0xc63d34 "window:%s") at bridge.c:805 #13 0x00c62558 in spi_atk_bridge_window_event_listener ( signal_hint=0xbfe90360, n_param_values=1, param_values=0x8f39648, data=0x8e927a0) at bridge.c:1278 #14 0x00e0cf7f in signal_emit_unlocked_R (node=<value optimized out>, detail=<value optimized out>, instance=0x8e7a570, emission_return=0x0, instance_and_params=0x8f39648) at gsignal.c:3213 #15 0x00e0e89d in IA__g_signal_emit_valist (instance=0x8e7a570, signal_id=140, detail=0, var_args=0xbfe9051c "") at gsignal.c:2980 #16 0x00e0ed57 in IA__g_signal_emit (instance=0x8e7a570, signal_id=140, detail=0) at gsignal.c:3037 #17 0x05007cfb in window_added (atk_obj=0x8e42140, index=0, child=0x8e7a570) at gailutil.c:481 #18 0x00e04f09 in IA__g_cclosure_marshal_VOID__UINT_POINTER ( closure=0x8e92750, return_value=0x0, n_param_values=3, param_values=0x8f278a0, invocation_hint=0xbfe906b0, marshal_data=0x5007c00) at gmarshal.c:672 #19 0x00df6643 in IA__g_closure_invoke (closure=0x8e92750, return_value=0x0, n_param_values=3, param_values=0x8f278a0, invocation_hint=0xbfe906b0) at gclosure.c:767 #20 0x00e0d4c0 in signal_emit_unlocked_R (node=<value optimized out>, detail=<value optimized out>, instance=0x8e42140, emission_return=0x0, instance_and_params=0x8f278a0) at gsignal.c:3247 #21 0x00e0e89d in IA__g_signal_emit_valist (instance=0x8e42140, signal_id=108, detail=506, var_args=0xbfe908d0 "") at gsignal.c:2980 #22 0x00e0ebe2 in IA__g_signal_emit_by_name (instance=0x8e42140, detailed_signal=0x500fe0c "children-changed::add") at gsignal.c:3074 #23 0x04fffb04 in gail_toplevel_show_event_watcher (ihint=0xbfe909a0, n_param_values=1, param_values=0x8eafcc8, data=0x8e42140) at gailtoplevel.c:251 #24 0x00e0cf7f in signal_emit_unlocked_R (node=<value optimized out>, detail=<value optimized out>, instance=0x8f1b8b8, emission_return=0x0, instance_and_params=0x8eafcc8) at gsignal.c:3213 #25 0x00e0e89d in IA__g_signal_emit_valist (instance=0x8f1b8b8, signal_id=13, detail=0, var_args=0xbfe90b5c "\001") at gsignal.c:2980 #26 0x00e0ed57 in IA__g_signal_emit (instance=0x8f1b8b8, signal_id=13, detail=0) at gsignal.c:3037 #27 0x00634205 in IA__gtk_widget_show (widget=0x8f1b8b8) at gtkwidget.c:3031 #28 0x00633f4d in IA__gtk_widget_show_all (widget=0x8f1b8b8) at gtkwidget.c:3179 #29 0x0806c1cd in process_event (on_window=<value optimized out>, keysym=<value optimized out>, event=<value optimized out>, window=<value optimized out>, screen=<value optimized out>, display=<value optimized out>, n_bindings=<value optimized out>, bindings=<value optimized out>) at core/keybindings.c:1218 #30 meta_display_process_key_event (on_window=<value optimized out>, keysym=<value optimized out>, event=<value optimized out>, window=<value optimized out>, screen=<value optimized out>, display=<value optimized out>, n_bindings=<value optimized out>, bindings=<value optimized out>) at core/keybindings.c:1373 #31 0x08062050 in event_callback (event=0xbfe90f6c, data=0x8eb1f70) at core/display.c:1589 #32 0x080a7e7f in filter_func (xevent=0xbfe90f6c, event=0x8e58f90, data=0x8eb67e0) at ui/ui.c:83 #33 0x00165d63 in gdk_event_apply_filters (filters=<value optimized out>, event=<value optimized out>, xevent=<value optimized out>) at gdkevents-x11.c:349 #34 gdk_event_translate (filters=<value optimized out>, event=<value optimized out>, xevent=<value optimized out>) at gdkevents-x11.c:917 #35 0x001685f1 in _gdk_events_queue (display=0x8e51000) at gdkevents-x11.c:2312 #36 0x00168b50 in gdk_event_dispatch (source=0x8e5b050, callback=0, user_data=0x0) at gdkevents-x11.c:2373 #37 0x00a5b0a8 in g_main_dispatch (context=<value optimized out>) at gmain.c:1960 #38 IA__g_main_context_dispatch (context=<value optimized out>) at gmain.c:2513 #39 0x00a5e9d8 in g_main_context_iterate (context=0x8e35cd8, block=<value optimized out>, dispatch=1, self=0x8e2f008) at gmain.c:2591 #40 0x00a5ee4f in IA__g_main_loop_run (loop=0x8e35dd8) at gmain.c:2799 #41 0x08070387 in main (argc=1, argv=0xbfe915f4) at core/main.c:589 at-spi-registryd is also hung. emacs itself looks fine, afaict. Switching to a console vt and then back seems to kick things enough that metacity finishes switching to the other window. Also, if you don't disable blink-cursor-mode in emacs, then metacity will wake up as soon as emacs's cursor blink timeout times out.
This bug appears to have been reported against 'rawhide' during the Fedora 12 development cycle. Changing version to '12'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
Can't immediately spot the hardlock in between Metacity and at-spi-registryd. I'm pretty sure that this isn't anything that Metacity is doing wrong nor has under its control. A backtrace from at-spi-registryd might reveal what it is waiting for - what Metacity is waiting for is at-spi-registryd to respond. It's probably not a coincidence that this involves Emacs which: A) Is going to load atk-bridge B) Is not a good GTK+ citizen Reassigning to at-spi.
This might be GNOME bug 392889 ( https://bugzilla.gnome.org/show_bug.cgi?id=392889 ) and/or related to Fedora bug 224611 ( https://bugzilla.redhat.com/show_bug.cgi?id=224611 ). I am seeing this symptom (alt-tab away from emacs hangs when a11y enabled).
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i can no longer reproduce this in F14