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locks


| 
| I have an application which uses two processes.  Since converting to CLIM i have
| a new problem which might be related to the fact that both processes can 
| be simultaneousely effecting the panes output history--yes this could be changed
| but it would require a great deal more work than i presently have budget for--.
| I saw the messages about using locks when interacting with the screen.  Could
| someone provide a short snippet of code showing how one would use those 
| unexported clim calls initial-lock-values and with-lockf? I understand how
| locks work but I don't have the foggiest which resources I need to associate
| with the lock in order to insure that one process doesn't change the output 
| history record while the other process is trying to access it.  Thanks.
| 

I wrote the question to which locks were the answer.  I had the same
problem you do.  Instead of using Clim locks, I used the locks in
Allegro's multi-processing system.  Since you have a multi-process
application, your lisp must have some sort of lock mechanism.  My code
is very simple.

In Allegro, mp is the multiprocess package.

  ;; This creates a globally accessible lock.
  (defvar display-lock (mp:make-process-lock))

In one process:

  ;; This waits until the lock is available before executing the body.
  ;; It then grabs the lock, locking out any other process that needs
  ;; this lock.  (display-line write to the 'messages pane in IDM-frame.)
  (mp:with-process-lock (display-lock)
       (mapc #'(lambda(L) (display-line L Stream)) Lines))

In the other process:

  ;; Same here.
  (mp:with-process-lock (display-lock)
       (redisplay-frame-pane IDM-frame (get-frame-pane IDM-frame 'messages)))


It seems to work!

-- Russ

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