Re: Race condition on loading packages from 2 maxima processes in parallel?

On 6/14/26 7:00 AM, David Scherfgen wrote:

> Gemini proposed this Common Lisp file locking mechanism (but read below):
>
> (defmacro with-file-lock ((lock-file &key (sleep-time 0.1)) &body body)
>   "Acquires an exclusive lock using purely ANSI Common Lisp atomic 
> file creation."
>   (let ((stream-sym (gensym "STREAM")))
>     `(let ((,stream-sym nil))
>        (unwind-protect
>            (progn
>              ;; Spinlock: keep trying to create the file until successful
>              (loop
>                (handler-case
>                    (progn
>                      (setf ,stream-sym (open ,lock-file
>                                              :direction :output
>                                              :if-exists :error
>  :if-does-not-exist :create))
>                      (return)) ; Successfully acquired lock; exit the loop
>                  (file-error ()
>                    ;; Lock file exists; wait and retry
>                    (sleep ,sleep-time))))
>              ;; Execute the compilation or protected code
>              ,@body)
>          ;; Cleanup: close the stream and delete the lock file
>          (when ,stream-sym
>            (close ,stream-sym)
>            (ignore-errors (delete-file ,lock-file)))))))
>
> I tried it by having multiple processes do this:
>
> (with-file-lock (".lockfile") (format t "Entered~%") (sleep 30) 
> (format t "Exited~%"))
>
> Seems to work ...
> There could be a problem, though, when a process crashes / gets killed 
> while it has the lock. Then it won't release the lock, and no process 
> could ever acquire it again.
> In theory, one could define a "timeout" and say that if the lockfile 
> exists and is too old (check using file-write-date), then the process 
> probably crashed.
I don’t think that’s terrible. You could limit the number of retries so 
that it eventually exits with an error. And it’s just a file, so I can 
always just remove the file myself.

I used to get these kinds of lock file errors in vi and emacs once in a 
while when the editor crashed while I was editing and/or saving the file.

​

_______________________________________________
Maxima-discuss mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/maxima-discuss