All Manuals > CAPI User Guide > 8 Modifying CAPI Windows > 8.6 Updating pane contents


8.6.1 Updating windows in real time

If your code needs to cause visible updates whilst continuing to do further computation, then you should run your computation in a separate thread which is not directly associated with the CAPI window.

Consider the following example where real work is represented by calls to sleep :

  1. Evaluate this code:
  2. (defun change-text (win text)
      (setf (title-pane-text win)
    (defun my-callback (win)
      (change-text win "Go")
       for i from 0 to 20 do 
       (change-text win (format nil "~D" i))
       (sleep 0.1)))
    (defun test ()
      (let* ((p1 (make-instance 'title-pane
                                :text "init"))
             (p2 (make-instance
                  'button :text "Go"
                  :callback-type :none
                  :callback #'(lambda ()
                                (my-callback p1)))))
         (make-instance 'row-layout :description (list p1 nil p2))
         :width 200 :height 200)))
  3. Run (test) and note that the updates do not appear until my-callback returns. This is because it uses only one thread.
  4. Now try this modified callback which uses a worker thread to perform the calculations:
  5. (defun my-work-function ()
      (let ((mbox (mp:ensure-process-mailbox)))
        ;; This should really have an error handler.
        (loop (let ((event (mp:process-read-event mbox
                            "Waiting for events")))
                (cond ((consp event)
                       (apply (car event) (cdr event)))
                      ((functionp event)
                       (funcall event)))))))
    (setf *worker*
          (mp:process-run-function "Worker process" ()
    (defun change-text (win text)
      (apply-in-pane-process win
                             #'(setf title-pane-text)
                             text win))
    (defun my-callback (win)
       #'(lambda ()
           (change-text win "Go")
            for i from 0 to 20 do 
            (change-text win (format nil "~D" i))
            (sleep 0.1)))))
  6. Run (test) again: you should see the updates appear immediately.

A real application might also display an Abort button during the computation, with a callback that aborts the worker process.

CAPI User Guide (Windows version) - 30 Aug 2011