intro.3xti

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3XTI 代码 · 共 107 行

.\"
.TH intro 3xti
.SH Name
intro \- introduction to the X/Open Transport Interface (XTI)
.SH Description
.NXR "X/Open Transport Interface" "introduction"
The X/Open Transport Interface defines a transport service 
interface that is independent of any specific transport provider. 
The interface is
provided by way of a set of library functions for the C programming 
language.
.SH Transport Providers
The transport layer can comprise one or more 
transport providers at the same time. The
transport provider identifier parameter passed to the 
.PN t_open()
function determines the required transport provider.
.SH Transport Endpoints
A transport endpoint specifies a communication path between 
a transport user and a
specific transport provider, which is identified by a local 
file descriptor \fI(fd)\fR. 
When a user opens a transport provider identifier, a 
local file descriptor
\fIfd\fR is returned that identifies the transport endpoint. 
.SH Synchronizing Endpoints 
One process can simultaneously open several \fIfd\fRs. In 
synchronous mode, however
the process must manage the different actions of the associated 
transport connections
sequentially. Conversely, several processes can share 
the same \fIfd\fR (by
.PN fork() 
or 
.PN dup() 
operations) but they have to synchronize themselves so as
not to issue a function that is unsuitable to the current state 
of the transport endpoint.
.SH Modes Of Service
The transport service interface supports two modes of service: 
connection mode and connectionless mode. A single 
transport endpoint cannot support both modes of service simultaneously.
.PP
The connection-mode transport service is circuit-oriented 
and enables data to be
transferred over an established connection in a reliable, 
sequential manner. In
contrast, the connectionless-mode transport service is 
message-oriented and supports
data transfer in self-contained units with no logical 
relationship required among multiple units.
.SH Error Handling
Two levels of error are defined for the transport interface. 
The first is the library
error level. Each library function has one or more error returns. 
A return of \-1 indicates 
a failure. An external integer, \fBt_errno\fR, which is defined in
the header file \fB<xti.h>\fR, holds the specific error number 
when such a failure
occurs. This value is set when errors occur but is not cleared on successful library
calls, so it should be tested only after an error has been indicated. If implemented,
a diagnostic function, 
\fBt_error\fR, prints out information on the current
transport error. The state of the transport provider may change if a transport error
occurs.
.PP
The second level of error is the operating system service routine level. A special
library level error number has been defined called [TSYSERR], which is generated
by each library function when the operating system service routine fails or some general
error occurs. When a function sets \fBt_errno\fR
to [TSYSERR], the specific
system error can be accessed through the external variable \fBerrno\fR.
.SH Key For Parameter Arrays
Each XTI function description, includes an array that summarizes the content of
the input and output parameter. The key is as follows:
.PP
.TS
tab(@);
lfHB lfHB
l l .
_
.sp 6p
Key@Description
.sp 6p
_
.sp 6p
x@T{
The parameter value is meaningful (input parameter must be set before the call and output parameter must be read after the call).
T}
(x)@T{
The content of the object pointed by the x pointer is meaningful.
T}
?@T{
The parameter value is meaningful, but the parameter is optional.
T}
(?)@T{
The content of the object pointed by the ? pointer is optional.
T}
/@The parameter value is meaningless.  \  \  \  \  \  \  \  \   
\= @T{
After the call, the parameter keeps the same value as before the call.
T}
.sp 6p
_
.TE
.\"