Abstact

New examples of IRAF applications interacting using a low-volume, socket-based text messaging scheme are described and demonstrated. The tasks may be distributed across multiple CPUs or locations, using a many-to-one or one-to-many client-server architecture.  Server applications respond to messages without blocking so other activities such as data processing, user interaction through a GUI, or responding to another client application, may take place.

Messaging is based on a simple text-based scheme consisting of either commands begining with a colon or data in keyword/value pairs.  This also allows any non-IRAF application which understands the protocol to participate as either a new client or server application.  The commands have the same form as IRAF GUI commands so that applications may easily interact with GUI tasks.

One such server application demonstrated is a GUI IRAF processing monitor.  IRAF (or non-IRAF) data reduction tasks send status and processing information to GUI server tasks which provide graphical displays and interaction with the received information.  One motivation for this is the powerful and easily customizable nature of IRAF GUIs by means of the GUI description files (which are currently TCL interpreted modules), and the need for such a component in the NOAO Mosaic Data Product Pipeline.  This pipeline uses multiple IRAF data reduction tasks and data parallel processing distributed across a network, requiring a central monitoring facility to ensure proper operation of the pipeline. Other applications of this messaging scheme are also discussed.

IRAF Server GUIs

The server GUIs are under development and the ones demonstrated here are prototypes.  The basic structure of the servers is:

• IRAF monitor server task
  
  
• Starts the OBM TCL GUI
• Enters a "cursor" loop blocking on input from the GUI
• The GUI periodically sends command to check for messages
• Task reads messages from any number of connections
• The reads do not block if there is no input or the clients disconnect
• The task manages and formats the data and feeds the GUI
  
  
• IRAF OBM GUI
  
  
• Customizable TCL script
• Communicates with server through simple text messages

Includes a timer callback to request the server check for new data


• IRAF client application task
  
  
• Requires very simple calls to send messages to the client
• Open FIO descriptor with special filename (eg inet:4566)
• Write to descriptor (typically with printf)
• Close descriptor
• If the server is not running the task fails to open the descriptor and

client can continue without sending messages and/or writing to a log file
• If the server disconnects (shutsdown) a trapable error occurs and

the client continues without sending message and/or writing to a log file

Figure 1: Messaging Architecture

New IRAF Monitor Servers

Keyword Monitor (see figure 2a and figure 2b)

• Receives keyword messages from various distributed processes
• The messages are grouped by a keyword to monitor and various associated keywords
• The last values received are displayed in a table along with statistics
• Alarm limits alert user of potential problems or poor data quality
• The set of values for the monitored may be graphed against any associated keyword
• The graphs may be displayed in two formats:
• A mnimal graph similar to a strip chart
• A full sized graph with axes
• Both graphs support full IRAF options

Figure 2a: Keyword monitor with small stripcharts

Figure 2b: Keyword monitor with expanded graph

Status Monitor (see figure 3)

• Receives keyword messages grouped by an identifier (typically an image name or id)
• The group contains a process identifier and a status
• A timer in GUI is used to warn of potentially hung processing steps

Figure 3: Status monitor mock-up

Technical Details

This paper discusses specific conventions and architectures for the servers presented here.  Other messaging conventions are possible as well as two-way communications.  So what  is described does not imply restrictions in the IRAF system or in the use of other messaging architectures for other purposes.

The message protocol consists of commands and keywords.   Examples of messages used with the Keyword Monitor are shown below.  The grouping is defined by the BEGIN/END cards.

BEGIN = CCDMEAN
TEMP = 370.
UT = 8:01:30.0
CCDMEAN = 46.
END = CCDMEAN
BEGIN = CCDMEAN
TEMP = 371.
UT = 8:01:39.0
CCDMEAN = 46.
END = CCDMEAN
 
• The IRAF application interface is standard text file I/O (FIO).  Messaging connections are specified by special filenames such as "inet:<port>" or "unix:<name>".  Non-blocking I/O is provided by trapping errors during file opens, reads, and writes.

 
• The IRAF VOS network device (ND) interface currently provides sockets.  In the future other types of messaging methods can be added such as a "message bus".  The applications would only need to specify a different type of filename.