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

Would a unwind-protect that removes the lock typically help in case of a crash? If power browns out while saving perhaps it is reasonable to remove the lock after waiting for 3 minutes or so... 

On 14 June 2026 16:00:19 CEST, David Scherfgen via Maxima-discuss <[email protected]> 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.
>For a robust solution, one should use e.g. POSIX flock.
>
>Best regards
>David Scherfgen
>
>Am So., 14. Juni 2026 um 15:40 Uhr schrieb Raymond Toy <
>[email protected]>:
>
>> On 6/14/26 5:05 AM, Gunter Königsmann via Maxima-discuss wrote:
>>
>> Dear all,
>>
>> wxMaxima on every commit creates a new virtual machine, compiles wxMaxima
>> in that machine and runs a few hundred tests in that machine.
>>
>> If it runs more than one test in parallel sometimes maxima fails to load
>> draw.
>>
>> My theory is:
>>
>>    - One maxima process tries to load draw, compiles that package and
>>    starts saving it.
>>    - A second maxima process tries to load the compiled draw package
>>    while that compiled package still being written.
>>
>> Could that be the case?
>>
>> Yes. Look at share/draw/draw.lisp. It runs mk:oos to compile all the
>> files from the draw package.
>> &#8203;
>> _______________________________________________
>> Maxima-discuss mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/maxima-discuss
>>

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