t_look(3)t_look(3)NAMEt_look - Look at the current event on a transport endpoint.
SYNOPSIS
#include <xti.h>
int t_look(
int fd );
LIBRARY
XTI Library (libxti.a)
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
t_look(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
The following table summarizes the relevance of the fd parameter when
t_look() is called:
─────────────────────────────────────
Parameter Before Call After Call
─────────────────────────────────────
fd y n
─────────────────────────────────────
Notes to Table This is a meaningful parameter. This is not a meaning‐
ful parameter. Specifies a file descriptor returned by the t_open()
function that identifies the local transport endpoint.
DESCRIPTION
The t_look() XTI function is used in connectionless and connection-ori‐
ented transport service to monitor the current event at the transport
endpoint specified by a file descriptor previously returned by the
t_open() function. The t_look() function permits a transport provider
to notify a transport user of any one of the nine asynchronous events
listed in the RETURN VALUE section when the transport user is calling
other XTI functions in synchronous mode.
During synchronous operation, all events at a transport endpoint are
saved by XTI so that any current event may be known to a transport
user. Each of the nine asynchronous events listed under the RETURN
VALUE section is defined by a symbolic name in the xti.h include file.
This symbolic name can be retrieved when the t_look() function is
called.
Some XTI functions fail unconditionally when they are called because
the current event at the transport endpoint does not permit them to
successfully execute. Four of the nine synchronous events listed in the
Event column of the following table cause unconditional failure when
any function listed in the Immediate T_LOOK Functions column is called.
Any of these four synchronous events requires that the transport user
be immediately notified. Unconditional failure returns a [T_LOOK] error
during execution of the currently called function or the next called
function when it is executed. This function can then be used to deter‐
mine which event occurred.
─────────────────────────────────────────────────────────────────
Event Immediate T_LOOK Func‐ Event Description
tions
─────────────────────────────────────────────────────────────────
T_LISTEN t_accept(), t_con‐ Connection indication
nect()*, t_unbind() received
T_DISCONNECT t_accept(), t_con‐ Disconnect received
nect(), t_listen()**,
t_rcv(), t_rcvcon‐
nect(), t_rcvrel(),
t_snd(), t_sndrel()
T_UDERR t_rcvudata(), t_sndu‐ Datagram error indica‐
data() tion
T_ORDREL t_rcvudata(), t_sndu‐ Orderly release indica‐
data() tion
─────────────────────────────────────────────────────────────────
Notes to Table Connection indication received at a transport endpoint
which has been bound with qlen > 0 (zero) and for which a connection
indication is pending (refer to the t_bind() function). Disconnect for
an outstanding connect indication.
When multiple events occur, the order in which their value is returned
is implementation dependent. All together, there are 11 XTI functions
that fail when a particular synchronous event requiring immediate noti‐
fication is detected.
The following table lists transport endpoint events and corresponding
functions to which a [T_LOOK] error is immediately returned when the
event causes function failure:
───────────────────────────────────────────────────────────────
Event Cleared with T_LOOK? Event Consuming Func‐
tions
───────────────────────────────────────────────────────────────
T_LISTEN No t_listen()
T_CONNECT No t_rcvconnect()
T_DATA No t_rcv(), t_rcvudata()
T_EXDATA No t_rcv()
T_DISCONNECT No t_rcvdis()
T_UDERR No t_rcvuderr()
T_ORDREL No t_rcvrel()
T_GODATA Yes t_snd(), t_sndudata()
T_GOEXDATA Yes t_snd()
───────────────────────────────────────────────────────────────
An event at a transport endpoint remains outstanding until a consuming
function clears it. Every event has an associated consuming function
that handles the event and clears it. The Event Consuming Function col‐
umn of the preceding table lists these events and the function that
clears each one when successfully executed.
RETURN VALUES
Upon successful completion, the t_look() function returns a value that
indicates which of the allowable events has occurred, or returns zero
if no event exists. One of the following events is returned: Connect
indication received. Connect confirmation received. Normal data
received. Expedited data received. Disconnect received. Datagram
error indication. Orderly release indication. Flow control restric‐
tions on normal data flow have been lifted. Normal data may be sent
again. Flow control restrictions on expedited data flow have been
lifted. Expedited data may be sent again.
Upon failure, the value -1 is returned and t_errno is set to indicate
the error.
ERRORS
If the t_look() function fails, t_errno is set to one of the following
values: The specified file descriptor does not refer to a transport
endpoint. A system error occurred during execution of this function.
This error indicates that a communication problem has been detected
between XTI and the transport provider for which there is no other
suitable XTI(t_errno).
VALID STATES
The t_look() function can be called in all transport provider states
except T_UNINIT.
SEE ALSO
Functions: t_bind(3), t_connect(3), t_listen(3), t_open(3), t_rcv(3),
t_rcvconnect(3), t_rcvdis(3), t_rcvrel(3), t_rcvudata(3), t_rcvud‐
err(3), t_snd(3), t_sndudata(3)
Standards: standards(5)
Network Programmer's Guide
t_look(3)
