t_look - Look at the current event on a transport endpoint.
#include <xti.h>
int t_look(
int fd );
XTI Library (libxti.a)
Interfaces documented on this reference page conform to
industry standards as follows:
t_look(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
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 meaningful parameter. Specifies a file descriptor
returned by the t_open() function that identifies the
local transport endpoint.
The t_look() XTI function is used in connectionless and
connection-oriented 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 determine
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_rcvconnect(),
t_rcvrel(),
t_snd(), t_sndrel()
T_UDERR t_rcvudata(), t_sndu- Datagram error indicadata()
tion
T_ORDREL t_rcvudata(), t_sndu- Orderly release indicadata()
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 notification 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 Functions
---------------------------------------------------------------
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 column of the preceding
table lists these events and the function that clears each
one when successfully executed.
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
restrictions 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.
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).
The t_look() function can be called in all transport
provider states except T_UNINIT.
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_rcvuderr(3), t_snd(3),
t_sndudata(3)
Standards: standards(5)
Network Programmer's Guide
t_look(3)
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