[fitsbits] xpa 2.1.6 public release

[Eric Mandel]

		   XPA: minimal buy-in messaging
                        Public Release 2.1.6
                            4 May 2005
                    http://hea-www.harvard.edu/saord

Summary
-------

We are pleased to announce the availability of a new public release of
the XPA messaging system (2.1.6).  This is a patch release: users are
encouraged to upgrade at their convenience. More information about the
XPA package (including download links) is available at the Web site:

	http://hea-www.harvard.edu/saord/xpa

XPA Description
---------------

The XPA messaging system provides seamless communication between many
kinds of Unix programs, including X programs and Tcl/Tk programs.  It
provides an easy way for users to communicate with XPA-enabled programs
by executing XPA client commands in the shell or by utilizing such
commands in scripts.  Because XPA works both at the programming level
and the shell level, it is a powerful tool for unifying any analysis
environment: users and programmers have great flexibility in choosing
the best level or levels at which to access XPA services, and client
access can be extended or modified at any time.

A program such as DS9 becomes an XPA-enabled server by defining named
points of public access through which data and commands can be
exchanged with other client programs (and users).  Using standard TCP
sockets as a transport mechanism, XPA supports both single-point and
broadcast messaging to and from these servers.  It supports direct
communication between XPA clients and servers, or indirect communication
via an intermediate message bus emulation program. Host-based access
control is implemented, as is as the ability to communicate with XPA
servers across a network.

Changes in this patch release include:

* Fixed race condition in cases where 2 or more servers makes client calls
  to one another.

* Generated PostScript and PDF versions of the help pages.

* Added ability to build shared libraries (done automatically with
  configure --enable-shared) with compilers other than gcc.

* Fixed bug in the XPA handler routine in which an access point was
  turned off if an error occurred in that routine (as opposed to the
  user-defined callback routine).

* Fixed race condition when "ack=false" flag (or -n) is used with XPASet()
  (or xpaset).

* Added defensive code to XPA handler to ensure that the passed XPA record
  is valid.

* Tcl/XPA servers such as ds9 were not turning off select() on the
  xpa channels inside an xpa callback, as required. This is now fixed.

* Added -P switch to xpans to enable experimental proxy support
  (default is disabled).  An argument of 1 processes proxy requests in
  the same thread as xpans requests, while an argument of 2 processes
  proxy requests in a separate thread.

* All memory allocation now performs error checking on the result.

Platforms and Availability
--------------------------

XPA consists of a library and a set of user programs.  Therefore, it
is most appropriately built from source.  XPA has been ported to
Linux, Solaris, Mac OSX (darwin) and various flavors of Windows
(NT/2000/ME/XP) using Cygwin. Once the source code tar file is
retrieved, XPA can be built and installed easily using standard
commands:

	./configure --prefix=<installdir> 	# configuration
	make					# build the software
	make install				# install in <installdir>

The package is available for download from the Web site:

	http://hea-www.harvard.edu/saord

Alternatively, it can be retrieved directly via anonymous ftp from
sao-ftp.harvard.edu in the pub/rd/xpa directory.

(NB: You must have Cygwin (www.cygwin.com) installed to build under Windows.)

Acknowledgments
----------------

Work on this project was performed with support from the Chandra X-ray
Science Center (NAS8-39073) and the Chandra High Resolution Camera
(NAS8-38248).

Mailing List
------------

A mailing list (saord-announce) have been set up using Brent Chapman's
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	subscribe saord-announce

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For more information (or to complain or encourage!)
---------------------------------------------------

Please send mail to: saord at cfa.harvard.edu.  We respond to questions,
bug reports, suggestions, gripes, and encouragement ...

						Eric Mandel
						eric at cfa.harvard.edu