qgetfd(3G)							    qgetfd(3G)

NAME    [Toc]    [Back]

     qgetfd - get the read file	descriptor associated with the event queue

C SPECIFICATION    [Toc]    [Back]

     long qgetfd(void)

PARAMETERS    [Toc]    [Back]

     none

FUNCTION RETURN	VALUE
     The returned function value is the	read file descriptor associated	with
     the event queue.  If there	is an error, the returned value	is a negative
     integer whose absolute value is an	error value defined in <errno.h>.

DESCRIPTION    [Toc]    [Back]

     qgetfd returns the	read file descriptor associated	with the event queue.
     The file descriptor can then be used with the select(2) system call.

EXAMPLE    [Toc]    [Back]

     The following example (presented in pseudo-code; not to be	typed
     verbatim) is suggested for	reading	events off of the GL queue using
     select(2):

	  FD_ZERO(&readfds);
	  if ((glfd = qgetfd())	< 0) {
	      printf("bad file descriptor %d0, glfd);
	      exit(-1);
	  }
	  for (;;) {
	      while (qtest()) {
		  .
		  .
		  blkqread()
		  .
		  .
	      }
	      /* Make sure all GL rendering which may be acting	as a prompt or
	       * cue for the user has completed	before checking	for a response
	       * from the user.
	       */
	      gflush();
	      FD_SET(glfd,&readfds);	   /* select with qgetfd descriptor   */
	      FD_SET(,);		   /* select with others descriptors  */
	      .
	      nfound = select (,&readfds,,,);
	      if (FD_ISSET(glfd,&readfds)) /* process queue events	      */
	       continue;
	      if (FD_ISSET(,)) {	   /* process other then queue events */
	       .
	       .
	      }
	  }



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qgetfd(3G)							    qgetfd(3G)



     The example provides two important	pieces of advice. First, use blkqread
     instead of	multiple qreads	because	it is more efficient.  Second, to
     ensure the	proper behavior	of select, call	qtest before and after you
     call select. When select indicates	data is	available on the file
     descriptor, there may not be GL event data	to read.  Similarly, there is
     a condition where select would block, but data is available. The use of
     qtest before and after select guards against this.

SEE ALSO    [Toc]    [Back]

     qread, gflush, select(2) (in the Programmer's Reference Manual)

NOTES    [Toc]    [Back]

     This routine is available only in immediate mode.

BUGS    [Toc]    [Back]

     The file descriptor returned by qgetfd will not be	detected as ready for
     reading by	the system call	select(2) when TIMER events are	inserted into
     the queue.	 Instead, one should use the timeout feature of	select(2) to
     achieve the same functionality.


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