On Tue, Jan 25, 2000 at 07:45:04AM +0000, Rick Welykochy wrote:
> Any socket programmers out there?
> A (simple) question, C++ code:
>
> 1. create a socket
> int const sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
>
> 2. bind to it
> unsigned int const port = 1234;
> unsigned long const listenaddr = INADDR_ANY;
> sockaddr_in listensock = { AF_INET, htons(listenport), { htonl(listenaddr) } };
> if (bind(sockfd, &listensock, sizeof(listensock)) != -1)
> ...
>
> The above sequence works fine the first time the program is
> run. An immediate second invocation fails at step 2, i.e.
> cannot bind to 0.0.0.0:1234.
The OS will not allow you to use the same host/port combination (in this
case, 0.0.0.0:1234) twice within a short period (Thats not entirely correct,
but it's close enough :) If you so a netstat during this period, which
is between about 1 and 4 minutes depending on the OS, you'll see a connection
in TIME_WAIT state on this port.
For full default, have a look at "TCP/IP Illustrated Volume 1" by W. Richard
Stevens, or do a websearch on "2msl", or possible time_wait.
Thankfully you can tell the OS to ignore it by putting the following between
1 and 2 above :
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on));
where "on" is defined above as :
int on = 1;
Scott.
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