<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML ><HEAD ><TITLE >When would you want to use a thread?</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="GStreamer Application Development Manual" HREF="index.html"><LINK REL="UP" TITLE="Threads" HREF="chapter-threads.html"><LINK REL="PREVIOUS" TITLE="Threads" HREF="chapter-threads.html"><LINK REL="NEXT" TITLE="Queues" HREF="chapter-queues.html"></HEAD ><BODY CLASS="sect1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" ><SPAN CLASS="application" >GStreamer</SPAN > Application Development Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="chapter-threads.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 21. Threads</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="chapter-queues.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="section-threads-when" >21.2. When would you want to use a thread?</A ></H1 ><P > 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. </P ><P > <A HREF="section-threads-when.html#section-threads-img" >Figure 21-1</A > shows how a thread can be visualised. </P ><DIV CLASS="figure" ><A NAME="section-threads-img" ></A ><P ><B >Figure 21-1. A thread</B ></P ><DIV CLASS="mediaobject" ><P ><IMG SRC="images/thread.png"></P ></DIV ></DIV ><P > As an example we show the helloworld program using a thread. </P ><P > <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 > </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="chapter-threads.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="chapter-queues.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Threads</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="chapter-threads.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Queues</TD ></TR ></TABLE ></DIV ></BODY ></HTML >