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3cda4e2eaa
Original commit message from CVS: sync with the current CVS glib API
139 lines
3.6 KiB
Text
139 lines
3.6 KiB
Text
<chapter id="cha-threads">
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<title>Threads</title>
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<para>
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GStreamer has support for multithreading throught the use of
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the <classname>GstThread</classname> object. This object is in fact
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a special <classname>GstBin</classname> that will become a thread when started.
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</para>
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<para>
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To construct a new thread you will perform something like:
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</para>
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<programlisting>
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GstElement *my_thread;
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// create the thread object
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my_thread = gst_thread_new ("my_thread");
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g_return_if_fail (audio_thread != NULL);
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// add some plugins
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gst_bin_add (GST_BIN (my_thread), GST_ELEMENT (funky_src));
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gst_bin_add (GST_BIN (my_thread), GST_ELEMENT (cool_effect));
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// connect the elements here...
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...
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// start playing
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gst_element_set_state (GST_ELEMENT (my_thread), GST_STATE_PLAYING);
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</programlisting>
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<para>
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The above program will create a thread with two elements in it. As soon
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as it is set to the PLAYING state, the thread will start to iterate.
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</para>
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<note>
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<para>
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A thread should normally contain a source element. Most often, the thread
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is fed with data from a queue.
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</para>
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</note>
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<para>
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A thread will be visualised as below
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</para>
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<figure float="1" id="sec-threads-img">
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<title>a thread</title>
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<graphic fileref="images/thread" format="png"></graphic>
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</figure>
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<para>
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As an example we show the helloworld program using a thread.
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</para>
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<programlisting>
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#include <gst/gst.h>
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/* eos will be called when the src element has an end of stream */
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void
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eos (GstSrc *src, gpointer data)
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{
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GstThread *thread = GST_THREAD (data);
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g_print ("have eos, quitting\n");
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/* stop the bin */
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gst_element_set_state (GST_ELEMENT (thread), GST_STATE_NULL);
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gst_main_quit ();
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}
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int
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main (int argc, char *argv[])
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{
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GstElement *disksrc, *audiosink;
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GstElement *pipeline;
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GstElement *thread;
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if (argc != 2) {
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g_print ("usage: %s <filename>\n", argv[0]);
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exit (-1);
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}
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gst_init (&argc, &argv);
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/* create a new thread to hold the elements */
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thread = gst_thread_new ("thread");
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g_assert (thread != NULL);
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/* create a new bin to hold the elements */
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pipeline = gst_pipeline_new ("pipeline");
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g_assert (pipeline != NULL);
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/* create a disk reader */
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disksrc = gst_elementfactory_make ("disksrc", "disk_source");
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g_assert (disksrc != NULL);
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g_object_set (G_OBJECT (disksrc), "location", argv[1], NULL);
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g_signal_connect (G_OBJECT (disksrc), "eos",
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G_CALLBACK (eos), thread);
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/* and an audio sink */
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audiosink = gst_elementfactory_make ("audiosink", "play_audio");
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g_assert (audiosink != NULL);
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/* add objects to the main pipeline */
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gst_bin_add (GST_BIN (pipeline), disksrc);
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gst_bin_add (GST_BIN (pipeline), audiosink);
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/* automatically setup the pipeline */
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if (!gst_pipeline_autoplug (GST_PIPELINE (pipeline))) {
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g_print ("unable to handle stream\n");
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exit (-1);
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}
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/* remove the source element from the pipeline */
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gst_bin_remove (GST_BIN (pipeline), disksrc);
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/* insert the source element in the thread, remember a thread needs at
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least one source or connection element */
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gst_bin_add (GST_BIN (thread), disksrc);
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/* add the pipeline to the thread too */
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gst_bin_add (GST_BIN (thread), GST_ELEMENT (pipeline));
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/* start playing */
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gst_element_set_state (GST_ELEMENT (thread), GST_STATE_PLAYING);
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/* do whatever you want here, the thread will be playing */
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...
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gst_main ();
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gst_pipeline_destroy (thread);
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exit (0);
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}
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</programlisting>
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</chapter>
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