Error Handling

This is a small overview as to how error handling might be handled.

GStreamer

gst_element_set_state() will return a GstStateChangeReturn value.

c

python

GstPipeline* pipeline = ...
GstStateChangeReturn ret = gst_element_set_state(GST_ELEMENT(pipeline), GST_STATE_PLAYING);

if (ret == GST_STATE_CHANGE_SUCCESS)
{
    // everything is wonderful
}
else if (ret == GST_STATE_CHANGE_ASYNC)
{
    // elements are still working
    // call gst_element_get_state()
    // to get a final result
}
else if (ret == GST_STAT_CHANGE_FAILURE)
{
    // The pipeline did not start
    // increase logging to find out what is happening
    // typical causes can be
    // - wrong caps
    // - elements cannot work with each other
    // - device cannot be opened
}
else
{
    // this means a GST_STATE_CHANGE_NO_PREROLL happens.
    // This case can be ignored.
}

pipeline = ...
change_ret = pipeline.set_state(Gst.State.PLAYING)

if change_ret == Gst.StateChange.SUCCESS:
    # everything is wonderful
    pass
elif change_ret == Gst.StateChange.ASYNC:
    # elements are still working
    # call gst_element_get_state()
    # to get a final result
    # to get a final result
    pass
elif ret == GST_STAT_CHANGE_FAILURE:
    # The pipeline did not start
    # increase logging to find out what is happening
    # typical causes can be
    # - wrong caps
    # - elements cannot work with each other
    # - device cannot be opened
    pass
else:
    # this means a Gst.StateChange.NO_PREROLL happens.
    # This case can be ignored.
    pass

tcam-property

tcam-property handles error by returning a GError to the user. All possible error types are defined in the enum TcamError

c

python

// explicitly initialize to NULL
// do this so that we can identify
// error
GError* err = NULL;

// some tcam-property API call

if (err) // an error occurred
{
    if (err->domain != tcam_error_quark())
    {
        // Not an error caused by tiscamera
        // handling is outside of the scope of this example
        return;
    }

    // err->message contains a human readable error description
    switch (err->code) // err->code contains the TcamError value
    {
        case TCAM_ERROR_UNKNOWN:
        {
            break;
        }
        case TCAM_ERROR_PROPERTY_NOT_WRITEABLE:
        {
            break;
        }
        case TCAM_ERROR_NO_DEVICE_OPEN:
        {
            //
            break;
        }
        case TCAM_ERROR_DEVICE_LOST:
        {
            printf("error: Device lost %s\n", err->message);
            // stop playback and other things
            break;
        }
        default:
        {
            printf("error: %s\n", err->message);
            break;
        }
    }
}

try:

    # some tcam-property call

except GLib.Error as err:

    if err.code == Tcam.Error.DEVICE_LOST:
        # stop playback and other things

    print("Error: {}".format(err.message))