LISTEN

C Interface

     listen(s, backlog)

     int s, backlog;

Description

To accept connections, a socket is first created with socket, a queue for incoming connections is specified with listen, and then connections are accepted with accept. The listen call applies only to unconnected sockets of type SOCK_STREAM. Note that you cannot call listen after accepthas been called. If the socket has not been bound to a local port before the listen is invoked, the system automatically binds a local port for the socket to listen on.

The listen queue is established for the socket specified by the s parameter, which is a socket descriptor.

The backlog parameter defines the maximum allowable length of the queue for pending connections. If a connection request arrives when the queue is full, the client receives an ETIMEDOUT error.

The backlog parameter is limited (silently) to be in the range of 1 to 128. If you specify any other value, the system automatically assigns the closest value within range.

Return Value

If the call is successful, 0 is returned. If the call fails, a -1 is returned, and an error code is stored in errno.

Errors

The following errors are returned by listen:

[EBADF]: The argument s is not a valid descriptor.
[EDESTADDRREQ]: No bind address was established.
[ENOTSOCK]: The argument s is not a socket.
[EOPNOTSUPP]: The socket is not of a type that supports the listen operation.
[ENOBUFS]: Series 300 only: No buffer space is available. The listen call cannot be started at this time.
[EINVAL]: The socket has been shut down or is already connected.

MPE/iX Specific

The backlog limit on MPE/iX is 128 as opposed to the backlog limit of 20 on HP-UX. When an HP-UX socket has performed a listen, the incoming connection requests are completed as they are received (up to the backlog limit). When using MPE/iX, connections are completed by the call to accept.

Author

UCB (University of California at Berkeley)