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>Chapter 23. Cothreads</H1
><P
> Cothreads are user-space threads that greatly reduce context switching overhead introduced by
regular kernel threads. Cothreads are also used to handle the more complex elements. They differ
from other user-space threading libraries in that they are scheduled explictly by GStreamer.
</P
><P
>
A cothread is created by a <CODE
CLASS="classname"
>GstBin</CODE
> whenever an element is found
inside the bin that has one or more of the following properties:
<P
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><LI
><P
> The element is loop-based instead of chain-based
</P
></LI
><LI
><P
> The element has multiple input pads
</P
></LI
><LI
><P
> The element has the MULTI_IN flag set
</P
></LI
></UL
>
The <CODE
CLASS="classname"
>GstBin</CODE
> will create a cothread context for all the elements
in the bin so that the elements will interact in cooperative
multithreading.
</P
><P
>
Before proceding to the concept of loop-based elements we will first
explain the chain-based elements.
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>23.1. Chain-based elements</A
></H1
><P
> Chain based elements receive a buffer of data and are supposed
to handle the data and perform a gst_pad_push.
</P
><P
> The basic main function of a chain-based element is like:
</P
><PRE
CLASS="programlisting"
> static void
chain_function (GstPad *pad, GstBuffer *buffer)
{
GstBuffer *outbuffer;
....
// process the buffer, create a new outbuffer
...
gst_pad_push (srcpad, outbuffer);
}
</PRE
><P
> Chain based function are mainly used for elements that have a one to one
relation between their input and output behaviour. An example of such an
element can be a simple video blur filter. The filter takes a buffer in, performs
the blur operation on it and sends out the resulting buffer.
</P
><P
> Another element, for example, is a volume filter. The filter takes audio samples as
input, performs the volume effect and sends out the resulting buffer.
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