Sockets

9.2.8t_listen()

This function tells the socket library that socket is going to be used for accepting connections from other hosts.

Syntax

extern long t_listen(long socket, int backlog)

where:

socket is the socket to be used for accepting connections.

backlog defines the maximum length to which the queue of pending connections can grow. If a connection request arrives when the queue is full, the client receives the error message ECONNREFUSED.

Return value

Returns one of the following:

Usage

To accept connections:

1.A socket is created with t_socket().

2.A backlog for incoming connections is specified with t_listen().

3.The connections are then accepted with t_accept().

The t_listen() call applies only to SOCK_STREAM sockets.

Sockets

9.2.9t_recv() and t_recvfrom()

These functions are used to receive messages from another socket.

Syntax

int t_recv(long socket, char *buffer, int length, int flags)

int t_recvfrom(long socket, char *buffer, int length, int flags, struct sockaddr *from)

Return value

Returns one of the following:

the number of bytes received

Sockets

Usage

The t_recv() function can be used only on a connected socket (see t_connect()). The t_recvfrom() function can be used to receive data on a socket, whether it is in a connected state or not.

If no messages are available at the socket, the receive call waits for a message to arrive. If the socket is nonblocking (see t_setsockopt() on page 9-20), –1 is returned, with the external socket errno set to EWOULDBLOCK.

The t_select() function can be used to determine when more data arrives.

Sockets

9.2.10t_select()

This function examines the input/output descriptor sets (whose addresses are passed in readfds, writefds, and exceptfds) to see if some of their descriptors are ready for reading, ready for writing, or have an exceptional condition pending. On return, t_select() replaces the given descriptor sets with subsets consisting of the descriptors that are ready for the requested operation. The total number of ready descriptors in all the sets is returned.

Syntax

int t_select(fd_set *readfds, fd_set *writefds, fd_set *exceptfds, long timeout)

readfds is the set of socket descriptors to be tested for available data to be read.

writefds is the set of socket descriptors to be tested for available buffer space for write operations.

exceptfds is the set of socket descriptors to be tested for pending exceptional conditions (if out-of-band data is available to be read).

timeout is the wait interval in TPS. If timeout is neither 0 nor –1, it specifies the maximum number of clock ticks (at TPS ticks per second) to wait for the selection to complete. If timeout is zero, t_select() modifies the descriptor sets to indicate which are ready for the requested operation, and returns immediately. If timeout is –1, t_select() blocks until at least one of the requested operations is ready, and there is no timeout.

Return value

Returns one of the following: positive value

Usage

The parameters readfds, writefds, and exceptfds can be given as NULL pointers if no descriptors are of interest.

Sockets

To determine if a call to t_accept() will return immediately, call t_select(), passing the socket as a member of the readfds set.

Note

Under rare circumstances, t_select() may indicate that a descriptor is ready for writing when, in fact, an attempt to write would block. This can happen if system resources necessary for a write are subsequently exhausted after the select has returned or are otherwise unavailable. If an application deems it critical that writes to a socket descriptor do not block, it should set the descriptor for nonblocking input/output using the SO_NBIO request to t_setsockopt().

The descriptors are stored within the fd_set structures as opaque objects. The macros below are provided for manipulating such structures.

The behavior of these macros is undefined if an invalid descriptor value is passed.

FD_ZERO FD_ZERO(fd_set *fdset)

This macro initializes a descriptor set fdset to the null set.

FD_SET FD_SET(long fd, fd_set *fdset)

This macro includes a particular socket descriptor fd in fdset.

FD_CLR FD_CLR(long fd, fd_set *fdset)

This macro removes fd from fdset.

FD_ISSET FD_ISSET(long fd, fd_set *fdset)

This macro is nonzero if fd is a member of fdset, and zero otherwise.