XPAInfoNew(3) define an XPA info public access point


#include <xpa.h>
XPA XPAInfoNew(char *class, char *name,
int (*info_callback)(),
void *info_data, char *info_mode);


[NB: this is an experimental interface, new to XPA 2.0, whose value and best use is evolving.]

A program can register interest in receiving a short message about a particular topic from any other process that cares to send such a message. Neither has to be an XPA server. For example, if a user starts to work with a new image file called new.fits, she might wish to alert interested programs about this new file by sending a short message using xpainfo:

  xpainfo IMAGEFILE /data/new.fits

In this example, each process that has used the XPAInfoNew() call to register interest in messages associated with the identifier IMAGEFILE will have its info_callback() executed with the following calling sequence:

  int info_cb(void *info_data, void *call_data, char *paramlist)
    XPA xpa = (XPA)call_data;

The arguments passed to this routine are equivalent to those sent in the send_callback() routine. The main difference is that there is no buf sent to the info callback: this mechanism is meant for short announcement of messages of interest to many clients.

The mode string is of the form: ``key1=value1,key2=value2,...'' The following keywords are recognized:

  key           value           default         explanation
  ------        --------        --------        -----------
  acl           true/false      true            enable access control

Because no buf is passed to this callback, the usual buf-related keywords are not applicable here.

The information sent in the parameter list is arbitrary. However, we envision sending information such as file names or XPA access points from which to collect more data. Note that the xpainfo program and the XPAInfo() routine that cause the info_callback to execute do not wait for the callback to complete before returning.