xpamainloop(3)							SAORD Documentation						    xpamainloop(3)

NAME

       XPAMainLoop -  optional main loop for XPA

SYNOPSIS

	 #include <xpa.h>

	 void XPAMainLoop();

DESCRIPTION

       Once XPA access points have been defined, a program must enter an event loop to watch for requests from external programs. This can be done
       in a variety of ways, depending on whether the event loop is processing events other than XPA events.  In cases where there are no non-XPA
       events to be processed, the program can simply call the XPAMainLoop() event loop.  This loop is implemented essentially as follows (error
       checking is simplified in this example):

	 FD_ZERO(&readfds);
	 while( XPAAddSelect(NULL, &readfds) ){
	   if( sgot = select(swidth, &readfds, NULL, NULL, NULL) >0 )
	     XPAProcessSelect(&readfds, 0);
	   else
	     break;
	   FD_ZERO(&readfds);
	 }

       The XPAAddSelect() routine sets up the select() readfds variable so that select() will wait for I/O on all the active XPA channels.  It
       returns the number of XPAs that are active; the loop will end when there are no active XPAs. The standard select() routine is called to
       wait for an external I/O request.  Since no timeout struct is passed in argument 5, the select() call hangs until there is an external
       request.  When an external I/O request is made, the XPAProcessSelect() routine is executed to process the pending requests.  In this rou-
       tine, the maxreq value determines how many requests will be processed: if maxreq <=0, then all currently pending requests will be pro-
       cessed.	Otherwise, up to maxreq requests will be processed.  (The most usual values for maxreq is 0 to process all requests.)

       If a program has its own Unix select() loop, then XPA access points can be added to it by using a variation of the standard XPAMainLoop:

	 XPAAddSelect(xpa, &readfds);
	 [app-specific ...]
	 if( select(width, &readfds, ...) ){
	   XPAProcessSelect(&readfds, maxreq);
	   [app-specific ...]
	   FD_ZERO(&readfds);
	 }

       XPAAddSelect() is called before select() to add the access points.  If the first argument is NULL, then all active XPA access points are
       added. Otherwise only the specified access point is added.  After select() is called, the XPAProcessSelect() routine can be called to
       process XPA requests.  Once again, the maxreq value determines how many requests will be processed: if maxreq <=0, then all currently pend-
       ing requests will be processed.	Otherwise, up to maxreq requests will be processed.

       XPA access points can be added to Xt event loops (using XtAppMainLoop()) and Tcl/Tk event loops (using vwait and the Tk loop).  When using
       XPA with these event loops, you only need to call:

       int XPAXtAddInput(XtAppContext app, XPA xpa)

       or

	 int XPATclAddInput(XPA xpa)

       respectively before entering the loop.

SEE ALSO

       See xpa(7) for a list of XPA help pages

version 2.1.14							   June 7, 2012 						    xpamainloop(3)