what I want: sockets on system1 to realize the other end on system2 is dead, so select() returns an exception condition on the socket to the dead system. I want this to happen within about 5 seconds of yanking the network or AC cable to System2.
What I get: system1 'realizes' system2 is unplugged about 2 minutes after the fact.
What I do: setsockopts on each socket opened between system1 & 2 as follows:
int SetSocketOptions(int fd)
{
int errval = 0;
if (fd >= 0)
{
int val = 1;
int step = 0;
struct linger myLinger = {1,0}; // wait 0 seconds for data to drain from the OutQ before returning from close(); cause RST/ABORT on this socket.
#define MAYBEDO(a,b,c,d,e,f,g) { if ((a) == 0) {(a) |= setsockopt(c,d,e,f,g); b++;}}
MAYBEDO(errval,step,fd,SOL_SOCKET,SO_LINGER,&myLinger,sizeof(myLinger));
// man ip: A TCP local socket address that has been bound is unavailable for
// some time after closing, unless the SO_REUSEADDR flag has been set. Care
// should be taken when using this flag as it makes TCP less reliable.
MAYBEDO(errval,step,fd,SOL_SOCKET,SO_REUSEADDR,&val,sizeof(val));
val = 1;
MAYBEDO(errval,step,fd,SOL_SOCKET,SO_KEEPALIVE,&val,sizeof(val));
// Cause 2 second wait before first keepalive, a 2 second interval between them, and a max count of 2 before giving up on the socket.
val = 2;
MAYBEDO(errval,step,fd,SOL_TCP,TCP_KEEPINTVL,&val,sizeof(val));
MAYBEDO(errval,step,fd,SOL_TCP,TCP_KEEPIDLE,&val,sizeof(val));
MAYBEDO(errval,step,fd,SOL_TCP,TCP_KEEPCNT,&val,sizeof(val));
// Do not delay transmission to coalesce packets (Nagle Algorithm); each should go promptly by itself.
MAYBEDO(errval,step,fd,IPPROTO_TCP, TCP_NODELAY,&val,sizeof(val));
if (errval)
{
printf("setsockopt(%d) returned error %s step %d ", fd, strerror(errno), step);
}
}
else errval = fd; // any non-zero return will do.
return errval;
}
Brian Brunner
brian.t.brunner@xxxxxxxxxxxxxxx
(610)796-5838
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