select() a pojmenovane fifo

[Petr Janda]

On Mon, Jul 03, 2006 at 12:32:09AM +0200, Martin Kezlinek wrote:
> >Zdravim
> >
> >mam problem s chovanim select() pro sledovani pojmenovane fifo.
> >
> >program velmi zjednodusene vypada takto:
> >
> >// --------------------------------------------
> >int fifo_fd, rc;
> >FILE *fifo_file;
> >struct timeval timeout;
> >fd_set fdset;
> >
> >int main(int argc, char **argv)
> >{
> >fifo_fd = open("fifo", O_RDONLY | O_NONBLOCK);
> >fifo_file = fdopen(fifo_fd, "r");
> >while (1) {
> >FD_ZERO(&fdset);
> >FD_SET(fifo_fd, &set);
> >timeout.tv_sec = 1;
> >timeout.tv_usec = 0;
> >rc = select(fifo_fd + 1, &fdset, NULL, NULL, &timeout);
> >if (rc > 0) {
> >// zpracuj data z fifo_file
> >} else if (rc < 0) {
> >// neco je spatne - chcipni 
> >}
> >// proved neco
> >}
> >}
> >// ---------------------------------------------
> >
> >
> >Moje potiz spociva v tom, ze 
> >- dokud do fifo nic nepise, tak select() spravne ceka timeout a pak 
> > vrati 0 ...
> >
> >- pokud ji neco otevre pro zapis, tak take ceka a pracuje podle
> > ocekavani (jsou data - navrat s 1, nesou data po timeout vraci 0)
> >
> >- pokud ji to neco zavre, tak 
> > - nedostanu SIGPIPE
> > - select vraci okamzite 1 pri kazdem pruchodu smyckou - to me stve
> >   nejvic
> > - pripadne cteni z fifo_file precte 0 byte a skonci s EOF
> >
> >distribuce debian unstable, jadro vlastni vanilla 2.6.16.20 + swsusp2,
> >libc 2.3.6-15
> >
> >Predpokladam, ze se me tyka odstavec na konci manualu select()
> >
> >Under Linux, select() may report a socket file descriptor as "ready for
> >reading",  while  nevertheless a subsequent read blocks. This could for
> >example happen when data has arrived but  upon examination  has  wrong
> >checksum  and is discarded. There may be other circumstances in which a
> >file descriptor is spuriously reported as ready.  Thus it may be  safer
> >to use O_NONBLOCK on sockets that should not block.
> >
> >Resil to nekdo? Tusim, jak to obejit, ale nejake korektni reseni by se
> >hodilo.
> >Nebo jsem uplne vedle a chova se to jak ma?
> >
> >
> >S pozdravem 
> >
> >Petr Janda
> 
> A nepomuze pomoci FD_ISSET  se dotazat  na  stav co se vlastne stalo?

nepomuze, alepon podle man select. select() ma vracet pocet fd na
kterych je neco zajimaveho, a ja v tom fdset mam jen jeden.

> btw:  FD_SET(fifo_fd, &set); ..nema tam byt  &fdset ?

Jo, ale ten preklep je jen v mailu (bohuzel, kez by reseni bylo tak
snadne)

	
	S pozdravem 

				Petr Janda
--
email: janda_at_netbox_dot_cz