Re: Deadlock in Gst::init()

[José Alburquerque <jaalburquerque gmail com>]

On Sat, 2012-05-12 at 13:52 -0400, Kurt Miller wrote:
> >>> Here is the stack trace showing the recursive call to
> >>> gst_plugin_load_by_name():
> >>> 
> >>> #2  0x0009c065 in _rthread_mutex_lock (mutexp=0x7c1e6670, trywait=0, abstime=0x0) at /usr/src/lib/librthread/rthread_sync.c:127
> >>> #3  0x08c68ec2 in g_mutex_lock () from /usr/local/lib/libglib-2.0.so.3200.0
> >>> #4  0x02f1f3e5 in gst_plugin_load_file (filename=0x7c1f6580 "/usr/local/lib/gstreamer-0.10/libgstadder.so", error=0xcfbc0bc8)
> >>>    at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstplugin.c:722
> >>> #5  0x02f2022b in gst_plugin_load_by_name (name=0x7c3c2bf5 "adder") at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstplugin.c:1297
> >>> #6  0x02f2185d in gst_plugin_feature_load (feature=0x7c3c32e8) at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstpluginfeature.c:111
> >>> #7  0x0b5e3954 in gst_adder_get_type () at /usr/obj/ports/gstreamermm-0.10.10.1/gstreamermm-0.10.10.1/gstreamer/gstreamermm/adder.cc:29
> >>> #8  0x0ff679e1 in plugin_init (plugin=0x7c397d48) at /usr/obj/ports/gst-plugins-base-0.10.36/gst-plugins-base-0.10.36/gst/adder/gstadder.c:1322
> >>> #9  0x02f1e6ff in gst_plugin_register_func (plugin=0x7c397d48, desc=0x2ff66020, user_data=0x0)
> >>>    at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstplugin.c:557
> >>> #10 0x02f1f611 in gst_plugin_load_file (filename=0x7c1f6580 "/usr/local/lib/gstreamer-0.10/libgstadder.so", error=0xcfbc0dc8)
> >>>    at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstplugin.c:843
> >>> #11 0x02f2022b in gst_plugin_load_by_name (name=0x7c3c2bf5 "adder") at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstplugin.c:1297
> >>> #12 0x02f2185d in gst_plugin_feature_load (feature=0x7c3c32e8) at /usr/obj/ports/gstreamer-0.10.36/gstreamer-0.10.36/gst/gstpluginfeature.c:111
> >>> #13 0x0b5e3954 in gst_adder_get_type () at /usr/obj/ports/gstreamermm-0.10.10.1/gstreamermm-0.10.10.1/gstreamer/gstreamermm/adder.cc:29
> >>> #14 0x0b624d21 in Gst::wrap_init () at /usr/obj/ports/gstreamermm-0.10.10.1/gstreamermm-0.10.10.1/gstreamer/gstreamermm/wrap_init.cc:386
> >>> #15 0x0b6258d0 in initialize_wrap_system () at /usr/obj/ports/gstreamermm-0.10.10.1/gstreamermm-0.10.10.1/gstreamer/gstreamermm/init.cc:36
> >>> #16 0x0b625a77 in Gst::init (argc=@0xcfbc0fb4, argv=@0xcfbc0fb8)
> >>>    at /usr/obj/ports/gstreamermm-0.10.10.1/gstreamermm-0.10.10.1/gstreamer/gstreamermm/init.cc:53
> >>> #17 0x1c01d13c in Glib::PropertyProxy<Glib::ustring>::get_value ()
> 
> I'm curious why frame 8 above doesn't end up going
> recursive on Linux like it does for OpenBSD. When I step through
> The code on OpenBSD it seems unavoidable.

It's difficult to know exactly what's happening.  On this system,
stepping through the code from frame 8 goes to line 119 of gstadder.c
which looks like the following:

GST_BOILERPLATE (GstAdder, gst_adder, GstElement, GST_TYPE_ELEMENT);

Apparently, this macro (defined in gstutils.h of GStreamer) generates
standard functions (among other things) for plug-ins such as the
*_get_type() functions (gst_adder_get_type() in this case).  The stack
trace below confirms this:

#0  g_once_init_enter(location = 0x7ffff31494e8) at gthread.c:674
#1  gst_adder_get_type() at gstadder.c:119
#2  plugin_init(plugin = 0x725e70) at gstadder.c:1322
#3  gst_plugin_register_func(plugin = 0x725e70, desc = 0x7ffff3149460,
user_data = 0x0) at gstplugin.c:557
#4  gst_plugin_load_file(filename = 0x734230
"/opt/usr-jhbuild/lib/gstreamer-0.10/libgstadder.so", error =
0x7fffffffdd88) at gstplugin.c:843
#5  gst_plugin_load_by_name(name = 0x73333f "adder") at gstplugin.c:1297
#6  gst_plugin_feature_load(feature = 0x735480) at
gstpluginfeature.c:111
#7  gst_adder_get_type() at adder.cc:29
#8  Gst::wrap_init() at wrap_init.cc:384
#9  Gst::initialize_wrap_system() at init.cc:36
#10  Gst::init(argc = @0x7fffffffde9c: 2, argv = @0x7fffffffde90:
0x7fffffffe028) at init.cc:53
#11  main(argc = 2, argv = 0x7fffffffe028) at hello_world/main.cc:67

On this system, the function that is called is gst_adder_get_type() in
gstadder.c (of the gst-plugins-base module) and not the one in adder.cc
(of gstreamermm).

> 
> Thanks,
> -Kurt
> 

-- 
José