gst_init之后如何再打开GST DEBUG呢？

打开gstreamer debug一般方法是：export GST_DEBUG=filesrc:5这样的做法，然后运行程序。但是通过看gstreamer的代码，这个环境变量是在gst_init的时候被读取并设置的，具体是在init_pre这个函数里面。如果程序已经在运行了，gst_init已经做过了，这个时候要打开debug怎么办呢？（Media server就有这样的需求）。

通过看init_pre中的代码，发现很简单，直接调用gst_debug_set_threshold_for_name或gst_debug_set_default_threshold就可以。下面是测试代码：

#include <gst/gst.h>
#include <unistd.h>

GstElement *pipeline, *source, *sink;

int main(int argc, char *argv[])
{
    gst_init(&argc, &argv);

    // create elements
    pipeline = gst_pipeline_new("test-pipeline");
    source = gst_element_factory_make("filesrc", "file-source");
    sink = gst_element_factory_make("fakesink", "fake-sink");
    if (!pipeline || !source || !sink) {
        g_print("One element could not be created!\n");
        return 1;
    }

    // set file name
    g_object_set(G_OBJECT(source), "location", "/home/eric/rphonenfs/medias/Audios/lddgy.mp3", NULL);

    // put all elements into bin
    gst_bin_add_many(GST_BIN(pipeline), source, sink, NULL);

    // link together
    gst_element_link_many(source, sink, NULL);

    // change state to PAUSED
    g_print("Before debug on, Setting to PAUSED\n");
    gst_element_set_state(pipeline, GST_STATE_PAUSED);
    sleep(1);
    g_print("Then we set pipeline to NULL\n");
    gst_element_set_state(pipeline, GST_STATE_NULL);
    
    // try to open debug
    g_print("Open debug infos...\n");

    // This function call is from "init_pre" which be called in "gst_init_check"
    // gst_debug_set_threshold_for_name("filesrc", 5);
    gst_debug_set_default_threshold(5);

    g_print("Rechange pipeline to PAUSED\n");
    gst_element_set_state(pipeline, GST_STATE_PAUSED);
    sleep(1);
    g_print("Change pipeline to NULL and terminate.\n");
    gst_element_set_state(pipeline, GST_STATE_NULL);
    gst_object_unref(GST_OBJECT(pipeline));

    return 0;
}