DATE: 15 APR 76 1017-EST
FROM: JFH at MIT-DMS
SUBJECT: UNIQUE NUMBERS
MESSAGE-ID: [MIT-DMS].31269


1/ GENERATE A FILE, SECOND NAME TO BE USED AS UNIQUE
NUMBER -- WE KEEP IT IN ASCII, BUT BINARY WOULD BE OK
ALSO IF > 999999 NEEDED.

ALGORITHM:

1/ OPEN FILE TO READ, GET REAL NAME 2, CLOSE FILE
2/ TRY TO RENAME FILE, USING REAL NAMES, TO BE N+1
   E.G. FOO 69 --> FOO 70
3/ IF RENAME WINS, YOU HAVE YOUR UNIQUE NUMBER (USE N
   OR N+1, AS LONG AS ALL USERS DO THE SAME.
4/ IF RENAME LOSES (FILE NOT FOUND) SOMEBODY ELSE BEAT
   YOU TO IT, LOOP BACK TO 1 AND TRY AGAIN...

THIS RELIES ON THE SYSTEM CALL OF RENAMING TO BE 'ATOMIC',
WHICH APPEARS TO BE TRUE.

THIS MAY CAUSE SOME NUMBERS TO BE SKIPPED, IF ENOUGH JOBS
SIMULTANEOUSLY TRY TO GET A NUMBER.

MAYBE A LOBBY FOR A SYSTEM CALL TO ALLOCATE A UNIQUE NUMBER
OVER SYSTEM CRASHES WOULD BE IN ORDER ALSO.

				JACK