how to find out if a nonblocking socket is closed

jwstric2 · 04-02-2005, 12:34 PM

Is Socket Closed?

I have investigated this problem shown in the link. Does anyone know of a clean solution to this approach? Im dealing with select and it fall through on a closed socket and reads 0. But according to the select spec just because it falls through and reads 0, it may not indicate an error. Before I even became concerned with dealing with cleaning up sockets I noticed that select sometime fell through with sockets that had no available data.

randyding · 04-02-2005, 09:12 PM

select() doesn't tell you anything about an fd other than read/write has been detected. If the read fd_set triggers then you call read() on the fd to see if there is really data available or the fd has an error or was closed. The return code of read() is -1 on error, (see errno form more details in this case) and 0 if the remote side closed the connection.

jwstric2 · 04-02-2005, 11:47 PM

why does select sometimes randomly fall through when there is no data to read? i've had select fall through and when i read I get 0 bytes even though the other side is still open. maybe someone could help explain that one to me?

randyding · 04-03-2005, 10:14 AM

Besides timeout, sending a signal to the process causes select to return -1 and errno==EINTR. select must always have a loop around it to account for this and restart the select operation. Without seeing code I can't think of any other reason for this.