Opened 15 months ago

Last modified 3 months ago

#1325 new defect

qt-light egg: timers may put chicken into an inconsistent state

Reported by: retroj Owned by:
Priority: major Milestone: someday
Component: extensions Version: 4.11.0
Keywords: Cc:
Estimated difficulty:

Description

I have found that a Qt::Timer may be used to make callbacks into chicken faster than the callbacks themselves can finish. This puts chicken into an inconsistent state and causes a crash. Here is a test case - callback rate and count may need to be adjusted for faster machines.

(import chicken scheme)

(use qt-light)

(qt:init)

(let* ((thread-rate 0.025)
       (timer (qt:timer thread-rate)))
  (define (timer-callback)
    (let loop ((i 0))
      (if (< i 1e6)
          (loop (+ i 1))
          #t)))
  (qt:connect timer "timeout()" timer-callback)
  (qt:start timer)
  (qt:run))
$ ./minimal.scm 

Warning: excluded identifier doesn't exist in module foreign: foreign-declare

Warning: excluded identifier doesn't exist in module foreign: foreign-declare
csi: runtime.c:2797: C_save_and_reclaim: Assertion `av > C_temporary_stack_bottom || av < C_temporary_stack_limit' failed.
Aborted

Since Qt must be used for the main event loop in a Qt program, making timers safe to use would be fairly important for the qt-light egg. Without knowing much about the internals, I think that maybe a semaphore could be used to block a callback if a previous callback has not finished. When this occurs, it would be nice if the api also exposed a way for a chicken program to know that a callback was dropped, so that it could take an appropriate action.

Change History (1)

comment:1 Changed 3 months ago by sjamaan

It sounds like these callbacks are executed in a different thread. This is explicitly not supported. You could set up something in pure C which writes to a mailbox or some such (perhaps with the concurrent-native-callbacks egg)

So I don't think this is a bug. Can you maybe provide some more information about how this works in QT?

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