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>21.2. When would you want to use a thread?</A
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> If you are writing a GUI application, making the top-level bin a thread will make your GUI
more responsive. If it were a pipeline instead, it would have to be iterated by your
application's event loop, which increases the latency between events (say, keyboard presses)
and responses from the GUI. In addition, any slight hang in the GUI would delay iteration of
the pipeline, which (for example) could cause pops in the output of the sound card, if it is
an audio pipeline.
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<A
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>Figure 21-1</A
> shows how a thread can be visualised.
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>Figure 21-1. A thread</B
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>
As an example we show the helloworld program using a thread.
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> <PRE
CLASS="programlisting"
> /* example-begin threads.c */
#include <gst/gst.h>
/* we set this to TRUE right before gst_main (), but there could still
be a race condition between setting it and entering the function */
gboolean can_quit = FALSE;
/* eos will be called when the src element has an end of stream */
void
eos (GstElement *src, gpointer data)
{
GstThread *thread = GST_THREAD (data);
g_print ("have eos, quitting\n");
/* stop the bin */
gst_element_set_state (GST_ELEMENT (thread), GST_STATE_NULL);
while (!can_quit) /* waste cycles */ ;
gst_main_quit ();
}
int
main (int argc, char *argv[])
{
GstElement *filesrc, *decoder, *audiosink;
GstElement *thread;
if (argc < 2) {
g_print ("usage: %s <Ogg/Vorbis filename>\n", argv[0]);
exit (-1);
}
gst_init (&argc, &argv);
/* create a new thread to hold the elements */
thread = gst_thread_new ("thread");
g_assert (thread != NULL);
/* create a disk reader */
filesrc = gst_element_factory_make ("filesrc", "disk_source");
g_assert (filesrc != NULL);
g_object_set (G_OBJECT (filesrc), "location", argv[1], NULL);
g_signal_connect (G_OBJECT (filesrc), "eos",
G_CALLBACK (eos), thread);
/* create an ogg decoder */
decoder = gst_element_factory_make ("vorbisfile", "decoder");
g_assert (decoder != NULL);
/* and an audio sink */
audiosink = gst_element_factory_make ("osssink", "play_audio");
g_assert (audiosink != NULL);
/* add objects to the thread */
gst_bin_add_many (GST_BIN (thread), filesrc, decoder, audiosink, NULL);
/* link them in the logical order */
gst_element_link_many (filesrc, decoder, audiosink, NULL);
/* start playing */
gst_element_set_state (thread, GST_STATE_PLAYING);
/* do whatever you want here, the thread will be playing */
g_print ("thread is playing\n");
can_quit = TRUE;
gst_main ();
gst_object_unref (GST_OBJECT (thread));
exit (0);
}
/* example-end threads.c */
</PRE
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