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>3.4. The Event Loop</A
></H1
><P
>&#13;	All commands in libraw1394 are asynchronous, with some
	synchronous wrapper functions for some types of transactions.
	This means that there are two streams of data, one going into
	raw1394 and one coming out.  With this design you can send out
	multiple transactions without having to wait for the response
	before you can continue (sending out other transactions, for
	example).  The responses and other events (like bus resets and
	received isochronous packets) are queued, and you can get them
	with <CODE
CLASS="function"
>raw1394_loop_iterate()</CODE
> or
	<CODE
CLASS="function"
>raw1394_loop_iterate_timeout()</CODE
> (which
	always returns after a user-specified timeout if no
	raw1394 event has occurred).
      </P
><P
>&#13;	This forms an event loop you may already know from similar systems like
	GUI toolkits.  <CODE
CLASS="function"
>raw1394_loop_iterate()</CODE
> gets one
	message from the event queue in raw1394, processes it with the
	configured callback functions and returns the value returned by the
	callback (so you can signal to the main loop from your callback; the
	standard callbacks all return 0).  It normally blocks when there are no
	events and always processes only one event.  If you are only receiving
	broadcast events like isochronous packets you thus have to set up a loop
	continuously calling the iterate function to get your callbacks called.
      </P
><P
>&#13;	Often it is necessary to have multiple event loops and combine
	them, e.g. if your application uses a GUI toolkit which also
	has its own event loop.  In that case you can use
	<CODE
CLASS="function"
>raw1394_get_fd()</CODE
> to get the file
	descriptor used for this handle by libraw1394.  The fd can be
	used to for <CODE
CLASS="function"
>select()</CODE
> or
	<CODE
CLASS="function"
>poll()</CODE
> calls together with the other
	loop's fd. (Most toolkits, like GTK and Qt, have special APIs
	for integrating file descriptors into their own event loops).
      </P
><P
>&#13;        If using <CODE
CLASS="function"
>poll()</CODE
>, you must test for
	<CODE
CLASS="symbol"
>POLLIN</CODE
> and <CODE
CLASS="symbol"
>POLLPRI</CODE
>
	events. If using <CODE
CLASS="function"
>select()</CODE
>, you must test
	for both read and exception activity.
      </P
><P
> If any of these conditions trigger, you should then call
        <CODE
CLASS="function"
>raw1394_loop_iterate()</CODE
> to pick up the
        event. <CODE
CLASS="function"
>raw1394_loop_iterate()</CODE
> is
        guaranteed not to block when called immediately after select()
        or poll() indicates activity.  After the first call you
        continue the main event loop.  If more events wait, the
        <CODE
CLASS="function"
>select()</CODE
>/<CODE
CLASS="function"
>poll()</CODE
> will
        immediately return again.
      </P
><P
>&#13;	You can also use the fd to set the <CODE
CLASS="symbol"
>O_NONBLOCK</CODE
> flag with
	<CODE
CLASS="function"
>fcntl()</CODE
>.  After that, the iterate function will not
	block anymore but fail with <CODE
CLASS="symbol"
>errno</CODE
> set to
	<CODE
CLASS="symbol"
>EAGAIN</CODE
> if no events wait.  These are the only legal
	uses for the fd returned by <CODE
CLASS="function"
>raw1394_get_fd()</CODE
>.
      </P
><P
>&#13;	There are some functions which provide a synchronous wrapper for
	transactions, note that these will call
	<CODE
CLASS="function"
>raw1394_loop_iterate()</CODE
> continuously until their
	transaction is completed, thus having implicit callback invocations
	during their execution.  The standard transaction functions have names
	of the form <CODE
CLASS="function"
>raw1394_start_xxx</CODE
>, the synchronous
	wrappers are called <CODE
CLASS="function"
>raw1394_xxx</CODE
>.
      </P
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libraw1394-doc 2.1.2-1 / usr / share / doc / libraw1394-doc / libraw1394 / x96.html
