[Info-vax] counting-lock ?

[David Jones]

In message <91916ca0-728c-407a-8a35-eda05350180a at l31g2000vbp.googlegroups.com>,
  Pierre <pierre.bru at gmail.com> writes:
>I have a DECnet object which can serve various known queries on a
>database. these queries are resource consuming and I don't want more
>than (say) n=5 of them of the same type to run at the same time. I
>want the other one to be queued up for further processing.

Off the top of my head.

Have 2 DLM resource: A, B.

Acquire:
   1. Get EX mode lock on A.
   2. Get CR mode lock on B.
   3. Use $GETLKI to get GRANTCOUNT on B.
   4. If grantcount <= n then
         dequeue lock A
	 return success.
      endif
   5. convert lock B to PW mode with blocking
      AST.
   6. Wait for blocking AST or a timeout.
   7. if timeout then
	  dequeue B
	  dequeue A
          return error.
      endif
   9. convert lock B to CR mode.
  10. dequeue lock A
  11. return success.

Release:
   1. Convert lock B to CW mode. (signals waiter if queued.).
   2. Dequeue lock B

-------------------------------------------------------------------------

David L. Jones               |      Phone:    (614) 271-6718
Ohio State University        |      Internet:
140 W. 19th St.              |               jonesd at ecr6.ohio-state.edu
Columbus, OH 43210           |               vman+ at osu.edu

Disclaimer: I'm looking for marbles all day long.