qgetfd(3G)qgetfd(3G)NAMEqgetfd - get the read file descriptor associated with the event queue
C SPECIFICATION
long qgetfd(void)PARAMETERS
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>.
DESCRIPTIONqgetfd returns the read file descriptor associated with the event queue.
The file descriptor can then be used with the select(2) system call.
EXAMPLE
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
qread, gflush, select(2) (in the Programmer's Reference Manual)
NOTES
This routine is available only in immediate mode.
BUGS
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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