Get gstreamer bus messages using non-static message handler - c++

Question

I have created a program using gstreamer which listens to different ports (say 5) for rtp packets.
Now I have created a class (say GstClass) which creates the pipeline, and has a Callback function which listens to the bus messages (I need this message system to shut down the pipeline after a certain timeout).
The main function looks like this - 2 threads are created with 2 objects and the GstFunc is called in both threads. The first function would listen to port 5000 and the second would listen to port 5008
int main() {
char filepath1[ ]= "/home/rohan/Tornado1.raw";
char filepath2[ ]= "/home/rohan/Tornado2.raw";
unsigned int port1 = 5000;
unsigned int port2 = 5008;
GstClass GstObj1;
GstClass GstObj2;
boost::thread thrd1 { &GstClass::GstFunc, &GstObj1, filepath1, &port1 };
boost::thread thrd2 { &GstClass::GstFunc, &GstObj2, filepath2, &port2 };
thrd1.join();
thrd2.join();
return 0;
}
the class GstClass looks like this -
class GstClass {
protected:
//some other variables...
GMainLoop *msLoop;
public:
gboolean bus_call(GstBus *bus, GstMessage *message,
gpointer data);
void GstFunc(char *filepath, unsigned int *port);
};
For detailed function view please look at this example. Replace the function int main (int argc, char *argv[]) with void GstFunc(char *filepath, unsigned int *port) with appropriate changes.
The GstFunc looks like
void GstFunc(char *filepath, unsigned int *port)
GMainLoop *loop;
GstElement *pipeline, *source, *conv, *sink;
GstBus *bus;
guint bus_watch_id;
gst_init (NULL, NULL);
loop = g_main_loop_new (NULL, FALSE);
/* Create gstreamer elements */
pipeline = gst_pipeline_new ("audio-player");
source = gst_element_factory_make ("autoaudiosrc", "audiosource");
conv = gst_element_factory_make ("audioconvert", "converter");
sink = gst_element_factory_make ("autoaudiosink", "audio-output");
if (!pipeline || !source || !conv || !sink) {
g_printerr ("One element could not be created. Exiting.\n");
return -1;
}
/* we add a message handler */
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
bus_watch_id = gst_bus_add_watch (bus, bus_call, NULL);
gst_object_unref (bus);
gst_bin_add_many (GST_BIN (pipeline), source, conv, sink, NULL);
gst_element_link_many (GST_BIN (pipeline), source, conv, sink, NULL);
g_main_loop_run (loop);
gst_element_set_state (pipeline, GST_STATE_NULL);
gst_object_unref (GST_OBJECT (pipeline));
g_source_remove (bus_watch_id);
g_main_loop_unref (loop);
return 0;
}
Now the dilemma I am facing is with the static function (in example) bus_call(...).
Since I am creating 2 pipelines in 2 different threads which are listening to 2 different ports, I cannot have this function as static (shared between the objects). how can I make these 2 pipelines dis-joint from each other? Or how can I get this static bus_call(...) to become non-static?
simply removing static keyword didn't help and giving this error
error: invalid use of non-static member function ‘gboolean GstClass::bus_call(GstBus*, GstMessage*, gpointer)‘
Few Imp points
I have referred to this document which says To use a bus, attach a message handler to the bus of a pipeline using gst_bus_add_watch()
The gst_bus_add_watch() in the GstClass::GstFunc() (which callbacks the bus_call) is mapped to the header file gstbus.h and the the declaration is simply
GST_API
guint gst_bus_add_watch(GstBus * bus, GstBusFunc func, gpointer user_data);
My initial guess is that the gst_bus_add_watch is expecting the 2nd parameter to be a static function. I am not sure why though. What can be done here?
*********************** Question Edit 2 ***********************
Is it possible to add an argument to the bus_call like gboolean bus_call(GstBus *bus, GstMessage *message,gpointer data,**SOME POINTER TO THE OBJECT**)?
This way the function will remain static while having a pointer to the object calling it, and acting upon the objects (say close pipeline of that object).

Answer 1

I don't think you can get away with what you want. The signature for GstBusFunc(), the callback, is for a pointer to function, not pointer to member function. They're different things. (I've also failed with std::bind, fwiw).
I've done something very similar to what you describe, though not quite the same, but I took a different approach that might help you. You can use a static method, but you must pass a pointer to your pipeline class to gst_bus_add_watch. Inside your busCallback you dereference the pointer and off you go! You may need to implement some kind of locking scheme as well.
class MyPipeline {
GstElement *m_pipeline;
public:
MyPipeline(...);
static void gboolean busCallback(GstBus *bus, GstMessage *msg, gpointer p);
}
MyPipeline::MyPipeline(...)
{
// create pipeline...
m_pipeline = ...;
// bus callback, pass 'this' as arg for callback
GstBus *bus = gst_pipeline_get_bus(GST_PIPELINE(m_pipeline));
gst_bus_add_watch(bus, &MyPipeline::busCallback, this);
gst_object_unref(bus);
// ...
}
gboolean MyPipeline::busCallback(GstBus *, GstMessage *msg, gpointer p)
{
// get lock if needed...
// recover your class instance
MyPipeline *myPipeline = (MyPipeline *)p;
// do what you need to, free lock
return TRUE;
}