Thread: SIGIO How-to

Does anyone know of any good references on using SIGIO. I have searched around but have been able to find very little on the subject. I have taken a look at the fcntl man page which gives a bit of information on it, but am still unsure how it works.

Thanks for all of your help.

Okay, thanks. How do I find out for what file descriptor the signal is related to and what event has happened. I am looking around for a complete example but have been unable to find one.

After looking around the net I came across a presentation, which had a bit of information on it and what appears to be a code example. But I can not make heads nor tails of it.
Snippet 1:

Code:

int sigio_add_fd(int fd) { 
static const int signum=SIGRTMIN+1; 
static pid_t mypid=0; 
if (!mypid) mypid=getpid(); 
fcntl(fd,F_SETOWN,mypid); 
fcntl(fd,F_SETSIG,signum); 
fcntl(fd,F_SETFL,fcntl(fd,F_GETFL)|O_NONBLOCK|O_ASYNC); 
} 
int sigio_rm_fd(struct sigio* s,int fd) { 
fcntl(fd,F_SETFL,fcntl(fd,F_GETFL)&(~O_ASYNC)); 
}

Snippet 2:

Code:

for (;;) { 
timeout.tv_sec=0; 
timeout.tv_nsec=10000; 
switch (r=sigtimedwait(&s.ss,&info,&timeout)) { 
case -1: if (errno!=EAGAIN) error("sigtimedwait"); 
case SIGIO: puts("SIGIO queue overflow!"); return 1; 
} 
if (r==signum) handle_io(info.si_fd,info.si_band); 
}

I get the first part, about declaring interest, but have very little idea what is going on in the second bit. I believe that the call to sigtimedwait is getting it to wait for a signal.