ACCOUNTING_DAEMON
-----------------

The Daemon's main function is to track the accounting file ACCOUNTNG.DAT
and to create a parallel billing file complete with cost information.
To do this, it maintains several internal databases, generally in linked
list form.  One list contains charging rate information for the various
queues.  Another contains information about each process on the system,
including how much money each spent the last time it looked.  Costs are
maintained in an incremental manner, which allows for rate changes in
the midst of a session.

Most of the work performed by the Daemon is driven by ASTs.  The main
exception to this is writing out "snapshot" information periodically,
which is sufficiently time consuming that it is interruptable by nearly
any other activity.

Non-periodic activity (COST requests, LOGIN/OUT requests, closing accounting
files, etc.) are initiated by the receipt of a request from the user
interface via a VMS mailbox.  Periodic activities are entirely AST driven.

Major Functions:
----------------

Reading mailbox - The mailbox is read and the requests are parsed.
		     Requests for LOGIN cause creation of a new entry in
		     the active process list. COST updates an existing
		     entry.  LOGOUT calulates a final session cost and
		     marks the entry for deletion.
			
Reading binary  - The Digital file ACCOUNTNG.DAT is read sequentially
		     and a UWO CCS accounting record is cut whenever
		     a new record is encountered in the binary file.
		     If a LOGOUT entry is discovered this way, a final
		     COST is calculated and the internal entry is marked
		     for deletion at that time.

Snapshot        - The entries for all processes in the linked list
		     are updated.  The entire linked list is then
		     written to disk. Entries marked for deletion are
		     removed from the list.

Reading rates	- The rates are read at UWO CCS hourly since all rate
		     change boundaries are on the hour.  This involves
		     reading the rate file, and remembering the appropriate
		     rates for the coming hour.

Cost		- On demand, the rate information and incremental resources
		     used by a process is transformed into an incremental
		     charge, which is then added to the previous total.


Basic Algorithom
----------------

	When the Daemon is started, it reads initialization files.  For
	    a "normal" startup, the "snapshot" file is ignored.  However,
	    the Daemon is "restartable" (for example after closing its
	    files at midnight).  A restart operation requires that the
	    snapshot file be read and charges up to that time be remembered.
	The Daemon mailbox is then created.
	Event flags are set and a QIO request to read the mailbox
	    is issued.
	At this point the Daemon loops servicing mailbox requests and
	    timed event requests. The only way out of the loop is the
	    receipt of a NEW_DAY request, at which time the Daemon
	    finishes up with a final snapshot, and tidies up its billing
	    files before it exits.  The NEW_DAY request is always followed
	    immediately with a Daemon "restart", to maintain continuity.


Christopher D. Lee
CHRIS@UWOVAX.UWO.CDN