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.\" ========================================================================
.\"
.IX Title "xpainfo 3"
.TH xpainfo 3 "July 23, 2013" "version 2.1.15" "SAORD Documentation"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
\&\fBXPAInfo: send short message to one or more \s-1XPA\s0 servers\fR
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <xpa.h>
\&
\& int XPAInfo(XPA xpa,
\& char *template, char *paramlist, char *mode,
\& char **names, char **messages, int n);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Send a short paramlist message to one or more \s-1XPA\s0 servers whose
class:name identifier matches the specified
template.
.PP
A
template
of the form \*(L"class1:name1\*(R" is sent to the
\&\s-1XPA\s0 name server, which returns a list of at most n matching \s-1XPA\s0
servers. A connection is established with each of these servers and
the paramlist string is passed to the server as the data transfer
request is initiated. If an \s-1XPA\s0 struct is passed to the call, then the
persistent connections are updated as described above. Otherwise,
temporary connections are made to the servers (which will be closed
when the call completes).
.PP
The \fIXPAInfo()\fR routine does not send data from a buf to the \s-1XPA\s0
servers. Only the paramlist is sent. The semantics of the paramlist
is not formalized, but at a minimum is should tell the server how to
get more information. For example, it might contain the class:name
of the \s-1XPA\s0 access point from which the server (acting as a client)
can obtain more info using XPAGet.
.PP
A string containing the class:name and ip:port of each server is
returned in the name array. If a given server returned an error or
the server callback sends a message back to the client, then the
message will be stored in the associated element of the messages
array. The returned message string will be of the form:
.PP
.Vb 1
\& XPA$ERROR error\-message (class:name ip:port)
.Ve
.PP
or
.PP
.Vb 1
\& XPA$MESSAGE message (class:name ip:port)
.Ve
.PP
The return value will contain the actual number of servers that were
processed. This value thus will hold the number of valid entries in
the names and messages arrays, and can be used to loop through these
arrays. In names and/or messages is \s-1NULL\s0, no information is passed back
in that array.
.PP
The following keywords are recognized:
.PP
.Vb 3
\& key value default explanation
\& \-\-\-\-\-\- \-\-\-\-\-\-\-\- \-\-\-\-\-\-\-\- \-\-\-\-\-\-\-\-\-\-\-
\& ack true/false true if false, don\*(Aqt wait for ack from server
.Ve
.PP
When ack is false, \fIXPAInfo()\fR will not wait for an error return from the \s-1XPA\s0
server. This means, in effect, that XPAInfo will send its paramlist string
to the \s-1XPA\s0 server and then exit: no information will be sent from the server
to the client. This UDP-like behavior is essential to avoid race
conditions in cases where \s-1XPA\s0 servers are sending info messages to
other servers. If two servers try to send each other an info message
at the same time and then wait for an ack, a race condition will result and
one or both will time out.
.PP
\&\fBExample:\fR
.PP
.Vb 1
\& (void)XPAInfo(NULL, "IMAGE", "ds9 image", NULL, NULL, NULL, 0);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
See xpa(n) for a list of \s-1XPA\s0 help pages
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