Here is a backtrace from a frozen session (all threads). I have now had it happen when clicking stop or pause in the audacity UI, and not just the timeline.


(gdb) thread apply all bt

Thread 4 (Thread 0x7fd7eafc2700 (LWP 719)):
#0  0x00007fd7f6feaf03 in __poll (fds=<value optimised out>, nfds=<value optimised out>, timeout=<value optimised out>) at ../sysdeps/unix/sysv/linux/poll.c:87
#1  0x00007fd7f7805104 in g_main_context_poll (context=0x283daa0, block=<value optimised out>, dispatch=1, self=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3404
#2  g_main_context_iterate (context=0x283daa0, block=<value optimised out>, dispatch=1, self=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3086
#3  0x00007fd7f78059f2 in g_main_loop_run (loop=0x283da80) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3299
#4  0x00007fd7f6a7ac44 in gdbus_shared_thread_func (data=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./gio/gdbusprivate.c:276
#5  0x00007fd7f782c3e4 in g_thread_create_proxy (data=0x283db80) at /build/buildd/glib2.0-2.28.6/./glib/gthread.c:1897
#6  0x00007fd7f8afdd8c in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#7  0x00007fd7f6ff804d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
#8  0x0000000000000000 in ?? ()

Thread 3 (Thread 0x7fd7dfffe700 (LWP 725)):
#0  0x00007fd7f8b064bd in nanosleep () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00007fd7fc9d448c in wxMicroSleep (microseconds=<value optimised out>) at ../src/unix/utilsunx.cpp:191
#2  0x000000000050ad4c in AudioThread::Entry (this=0x2aa3eb0) at AudioIO.cpp:2168
#3  0x00007fd7fc9cf631 in wxThreadInternal::PthreadStart (thread=0x2aa3eb0) at ../src/unix/threadpsx.cpp:766
#4  0x00007fd7f8afdd8c in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#5  0x00007fd7f6ff804d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
#6  0x0000000000000000 in ?? ()

Thread 2 (Thread 0x7fd7daffb700 (LWP 1564)):
#0  0x00007fd7f8afffc5 in __pthread_mutex_lock_full () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00007fd7e8b29b7e in pa_mutex_lock () from /usr/lib/libpulsecommon-0.9.22.so
#2  0x00007fd7e9379339 in ?? () from /usr/lib/libpulse.so.0
#3  0x00007fd7e936b116 in pa_mainloop_poll () from /usr/lib/libpulse.so.0
#4  0x00007fd7e936b749 in pa_mainloop_iterate () from /usr/lib/libpulse.so.0
#5  0x00007fd7e936b800 in pa_mainloop_run () from /usr/lib/libpulse.so.0
#6  0x00007fd7e93792df in ?? () from /usr/lib/libpulse.so.0
#7  0x00007fd7e8b2aa88 in ?? () from /usr/lib/libpulsecommon-0.9.22.so
#8  0x00007fd7f8afdd8c in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#9  0x00007fd7f6ff804d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
#10 0x0000000000000000 in ?? ()

Thread 1 (Thread 0x7fd7fdbaa960 (LWP 717)):
#0  0x00007fd7f8aff06d in pthread_join () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00007fd7f901af5d in PaUnixThread_Terminate (self=0x30234f0, wait=<value optimised out>, exitResult=0x7fff883648fc) at src/os/unix/pa_unix_util.c:441
#2  0x00007fd7f900d2c3 in RealStop (stream=0x3023350, abort=<value optimised out>) at src/hostapi/alsa/pa_linux_alsa.c:3022
#3  0x000000000050534d in AudioIO::StopStream (this=0x2a34280) at AudioIO.cpp:1627
#4  0x00000000006bdf04 in ControlToolBar::StopPlaying (this=0x2c1eac0, stopStream=true) at toolbars/ControlToolBar.cpp:716
#5  0x00007fd7fc9d0ad5 in wxEvtHandler::ProcessEventIfMatches (entry=<value optimised out>, handler=<value optimised out>, event=...) at ../src/common/event.cpp:1239
#6  0x00007fd7fc9d0c5c in wxEventHashTable::HandleEvent (this=<value optimised out>, event=..., self=0x2c1eac0) at ../src/common/event.cpp:906
#7  0x00007fd7fc9d0f94 in wxEvtHandler::ProcessEvent (this=0x2c1eac0, event=...) at ../src/common/event.cpp:1301
#8  0x00007fd7fd12a3e9 in wxWindowBase::TryParent (this=<value optimised out>, event=...) at ../src/common/wincmn.cpp:2661
#9  0x00000000006d581e in AButton::Click (this=0x2c37c50) at widgets/AButton.cpp:389
#10 0x00000000006d5b56 in AButton::OnMouseEvent (this=0x2c37c50, event=...) at widgets/AButton.cpp:282
#11 0x00007fd7fc9d0ad5 in wxEvtHandler::ProcessEventIfMatches (entry=<value optimised out>, handler=<value optimised out>, event=...) at ../src/common/event.cpp:1239
#12 0x00007fd7fc9d0c5c in wxEventHashTable::HandleEvent (this=<value optimised out>, event=..., self=0x2c37c50) at ../src/common/event.cpp:906
#13 0x00007fd7fc9d0f94 in wxEvtHandler::ProcessEvent (this=0x2c37c50, event=...) at ../src/common/event.cpp:1301
#14 0x00007fd7fd04e888 in gtk_window_button_release_callback (widget=0x2b584d0, gdk_event=0x2e054a0, win=0x2c37c50) at ../src/gtk/window.cpp:1714
#15 0x00007fd7f8372578 in _gtk_marshal_BOOLEAN__BOXED (closure=0x2c3bfa0, return_value=0x7fff883650e0, n_param_values=<value optimised out>, param_values=0x2fe42f0, invocation_hint=<value optimised out>, 
    marshal_data=<value optimised out>) at /build/buildd/gtk+2.0-2.24.4/gtk/gtkmarshalers.c:86
#16 0x00007fd7f7abf81c in g_closure_invoke (closure=0x2c3bfa0, return_value=0x7fff883650e0, n_param_values=2, param_values=0x2fe42f0, invocation_hint=0x7fff883650a0) at /build/buildd/glib2.0-2.28.6/./gobject/gclosure.c:767
#17 0x00007fd7f7ad1019 in signal_emit_unlocked_R (node=<value optimised out>, detail=0, instance=0x2b584d0, emission_return=0x7fff88365250, instance_and_params=0x2fe42f0) at /build/buildd/glib2.0-2.28.6/./gobject/gsignal.c:3252
#18 0x00007fd7f7ad9fa9 in g_signal_emit_valist (instance=<value optimised out>, signal_id=<value optimised out>, detail=<value optimised out>, var_args=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./gobject/gsignal.c:2993
#19 0x00007fd7f7ada41f in g_signal_emit (instance=<value optimised out>, signal_id=<value optimised out>, detail=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./gobject/gsignal.c:3040
#20 0x00007fd7f848e4d1 in gtk_widget_event_internal (widget=0x2b584d0, event=0x2e054a0) at /build/buildd/gtk+2.0-2.24.4/gtk/gtkwidget.c:4988
#21 0x00007fd7f8370763 in IA__gtk_propagate_event (widget=0x2b584d0, event=0x2e054a0) at /build/buildd/gtk+2.0-2.24.4/gtk/gtkmain.c:2495
#22 0x00007fd7f8370a5b in IA__gtk_main_do_event (event=0x2e054a0) at /build/buildd/gtk+2.0-2.24.4/gtk/gtkmain.c:1685
#23 0x00007fd7f7fe35cc in gdk_event_dispatch (source=<value optimised out>, callback=<value optimised out>, user_data=<value optimised out>) at /build/buildd/gtk+2.0-2.24.4/gdk/x11/gdkevents-x11.c:2377
#24 0x00007fd7f7804bcd in g_main_dispatch (context=0x27bda60) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:2440
#25 g_main_context_dispatch (context=0x27bda60) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3013
#26 0x00007fd7f78053a8 in g_main_context_iterate (context=0x27bda60, block=<value optimised out>, dispatch=1, self=<value optimised out>) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3091
#27 0x00007fd7f78059f2 in g_main_loop_run (loop=0x28e5d70) at /build/buildd/glib2.0-2.28.6/./glib/gmain.c:3299
#28 0x00007fd7f836faf7 in IA__gtk_main () at /build/buildd/gtk+2.0-2.24.4/gtk/gtkmain.c:1257
#29 0x00007fd7fd03b578 in wxEventLoop::Run (this=<value optimised out>) at ../src/gtk/evtloop.cpp:76
#30 0x00007fd7fd0b83eb in wxAppBase::MainLoop (this=0x2858220) at ../src/common/appcmn.cpp:312
#31 0x00007fd7fc97e53a in wxEntry (argc=<value optimised out>, argv=<value optimised out>) at ../src/common/init.cpp:448
#32 0x0000000000500342 in main (argc=1, argv=<value optimised out>) at AudacityApp.cpp:638