.
Thread 4 (Thread 0x7fbf34335700 (LWP 3296)):
#0  0x00007fbf3d46c8dd in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007fbf3d9a2ebc in g_main_context_iterate (priority=2147483647, n_fds=1, fds=0x7fbf2c0010e0, timeout=-1, context=0xec4980) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:4103
        poll_func = 0x7fbf3d9b23e0 <g_poll>
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 1
        allocated_nfds = 1
        fds = 0x7fbf2c0010e0
#2  0x00007fbf3d9a2ebc in g_main_context_iterate (context=context@entry=0xec4980, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3803
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 1
        allocated_nfds = 1
        fds = 0x7fbf2c0010e0
#3  0x00007fbf3d9a2fcc in g_main_context_iteration (context=0xec4980, may_block=1) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3869
        retval = <optimized out>
#4  0x00007fbf3433d27d in  () at /usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so
#5  0x00007fbf3d9c9955 in g_thread_proxy (data=0xe75ca0) at /build/buildd/glib2.0-2.44.1/./glib/gthread.c:764
        thread = 0xe75ca0
#6  0x00007fbf3d7426aa in start_thread (arg=0x7fbf34335700) at pthread_create.c:333
        __res = <optimized out>
        pd = 0x7fbf34335700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140459191260928, 8030570150646519692, 0, 140729924491759, 140459191261632, 15485312, -8067009715627616372, -8067024551290202228}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
        __PRETTY_FUNCTION__ = "start_thread"
#7  0x00007fbf3d477eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
.
Thread 3 (Thread 0x7fbf33b34700 (LWP 3297)):
#0  0x00007fbf3d46c8dd in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007fbf3d9a2ebc in g_main_context_iterate (priority=2147483647, n_fds=2, fds=0x7fbf240010c0, timeout=-1, context=0x7fbf2c00f140) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:4103
        poll_func = 0x7fbf3d9b23e0 <g_poll>
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 2
        allocated_nfds = 2
        fds = 0x7fbf240010c0
#2  0x00007fbf3d9a2ebc in g_main_context_iterate (context=0x7fbf2c00f140, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3803
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 2
        allocated_nfds = 2
        fds = 0x7fbf240010c0
#3  0x00007fbf3d9a3242 in g_main_loop_run (loop=0x7fbf2c00f0d0) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:4002
        __FUNCTION__ = "g_main_loop_run"
#4  0x00007fbf3e1b0af6 in gdbus_shared_thread_func (user_data=0x7fbf2c00f110) at /build/buildd/glib2.0-2.44.1/./gio/gdbusprivate.c:274
        data = 0x7fbf2c00f110
#5  0x00007fbf3d9c9955 in g_thread_proxy (data=0xece590) at /build/buildd/glib2.0-2.44.1/./glib/gthread.c:764
        thread = 0xece590
#6  0x00007fbf3d7426aa in start_thread (arg=0x7fbf33b34700) at pthread_create.c:333
        __res = <optimized out>
        pd = 0x7fbf33b34700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140459182868224, 8030570150646519692, 0, 140459191257343, 140459182868928, 140459053740304, -8067013014699370612, -8067024551290202228}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
        __PRETTY_FUNCTION__ = "start_thread"
#7  0x00007fbf3d477eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
.
Thread 2 (Thread 0x7fbf326c1700 (LWP 3310)):
#0  0x00007fbf3d46c8dd in poll () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007fbf3d9a2ebc in g_main_context_iterate (priority=2147483647, n_fds=2, fds=0x7fbf1c0008c0, timeout=-1, context=0xf48470) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:4103
        poll_func = 0x7fbf3d9b23e0 <g_poll>
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 2
        allocated_nfds = 2
        fds = 0x7fbf1c0008c0
#2  0x00007fbf3d9a2ebc in g_main_context_iterate (context=context@entry=0xf48470, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3803
        max_priority = 2147483647
        timeout = -1
        some_ready = <optimized out>
        nfds = 2
        allocated_nfds = 2
        fds = 0x7fbf1c0008c0
#3  0x00007fbf3d9a2fcc in g_main_context_iteration (context=0xf48470, may_block=may_block@entry=1) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3869
        retval = <optimized out>
#4  0x00007fbf3d9a3009 in glib_worker_main (data=<optimized out>) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:5618
#5  0x00007fbf3d9c9955 in g_thread_proxy (data=0xecf940) at /build/buildd/glib2.0-2.44.1/./glib/gthread.c:764
        thread = 0xecf940
#6  0x00007fbf3d7426aa in start_thread (arg=0x7fbf326c1700) at pthread_create.c:333
        __res = <optimized out>
        pd = 0x7fbf326c1700
        now = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {140459161425664, 8030570150646519692, 0, 140729924492367, 140459161426368, 0, -8067013626195339380, -8067024551290202228}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0x0, 0x0}, data = {prev = 0x0, cleanup = 0x0, canceltype = 0}}}
        not_first_call = <optimized out>
        pagesize_m1 = <optimized out>
        sp = <optimized out>
        freesize = <optimized out>
        __PRETTY_FUNCTION__ = "start_thread"
#7  0x00007fbf3d477eed in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
.
Thread 1 (Thread 0x7fbf3f9369c0 (LWP 3295)):
#0  0x00007fbf3d3a6267 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:55
        resultvar = 0
        pid = 3295
        selftid = 3295
#1  0x00007fbf3d3a7eca in __GI_abort () at abort.c:89
        save_stage = 2
        act = {__sigaction_handler = {sa_handler = 0x4, sa_sigaction = 0x4}, sa_mask = {__val = {140729924489008, 140729924504270, 140729924489088, 47259892976, 140459146031104, 140459344138280, 140459331162192, 140459331163440, 18874442, 140729924489568, 140459343042716, 140459344157184, 140459344138280, 0, 140459342529712, 140459344122409}}, sa_flags = 830550016, sa_restorer = 0x7fbf3d501028}
        sigs = {__val = {32, 0 <repeats 15 times>}}
#2  0x00007fbf3d39f03d in __assert_fail_base (fmt=0x7fbf3d501028 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x7fbf3c8a1050 "((*&(&surface->ref_count)->ref_count) > 0)", file=file@entry=0x7fbf3c8a0fe0 "../../../../src/cairo-surface.c", line=line@entry=953, function=function@entry=0x7fbf3c8a1530 "cairo_surface_destroy") at assert.c:92
        str = 0x1174770 "\260H"
        total = 4096
#3  0x00007fbf3d39f0f2 in __GI___assert_fail (assertion=0x7fbf3c8a1050 "((*&(&surface->ref_count)->ref_count) > 0)", file=0x7fbf3c8a0fe0 "../../../../src/cairo-surface.c", line=953, function=0x7fbf3c8a1530 "cairo_surface_destroy") at assert.c:101
#4  0x00007fbf3c833212 in cairo_surface_destroy () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#5  0x00007fbf3c863080 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#6  0x00007fbf3c863d13 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#7  0x00007fbf3c833ad4 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#8  0x00007fbf3c7fc455 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#9  0x00007fbf3c7fcf6e in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#10 0x00007fbf3c830758 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#11 0x00007fbf3c830abe in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#12 0x00007fbf3c830b39 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#13 0x00007fbf3c7ebcc9 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#14 0x00007fbf3c833fbc in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#15 0x00007fbf3c7f3a44 in  () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#16 0x00007fbf3c7e66d1 in cairo_mask () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#17 0x00007fbf3c7e6786 in cairo_mask_surface () at /usr/lib/x86_64-linux-gnu/libcairo.so.2
#18 0x00007fbf3f227c24 in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#19 0x00007fbf3f2290c7 in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#20 0x00007fbf3f21ebef in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#21 0x00007fbf3f21f7d0 in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#22 0x00007fbf3f220a25 in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#23 0x00007fbf3f21396e in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#24 0x00007fbf3f2146c4 in  () at /usr/lib/x86_64-linux-gnu/libwnck-3.so.0
#25 0x00007fbf3d9a2b4d in g_main_context_dispatch (context=0xeb6260) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3122
        dispatch = 0x7fbf3d99f610 <g_idle_dispatch>
        prev_source = 0x0
        was_in_call = 0
        user_data = 0xedcb70
        callback = 0x7fbf3f2146b0
        cb_funcs = <optimized out>
        cb_data = 0x12007d0
        need_destroy = <optimized out>
        source = 0x1174700
        current = 0xed0670
        i = 0
#26 0x00007fbf3d9a2b4d in g_main_context_dispatch (context=context@entry=0xeb6260) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3737
#27 0x00007fbf3d9a2f20 in g_main_context_iterate (context=0xeb6260, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:3808
        max_priority = 200
        timeout = 0
        some_ready = 1
        nfds = <optimized out>
        allocated_nfds = 2
        fds = 0xf19b30
#28 0x00007fbf3d9a3242 in g_main_loop_run (loop=0xf058c0) at /build/buildd/glib2.0-2.44.1/./glib/gmain.c:4002
        __FUNCTION__ = "g_main_loop_run"
#29 0x00000000004122f1 in main ()