select() a pojmenovane fifo
Petr Janda
janda na netbox.cz
Pátek Červen 30 09:36:36 CEST 2006
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
--
email: janda_at_netbox_dot_cz
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