[Newbies] Screensaver detection

Michael van der Gulik mikevdg at gmail.com
Tue Feb 12 23:57:25 UTC 2008

On Feb 13, 2008 10:53 AM, Uwe Loew <uwe_loew at gmx.net> wrote:

>  Hello squeak professionals,
> in our process monitoring software we use a background process to update
> the displayed values.
> breakFlag := false.
> delay := Delay forMilliseconds: 10.
> Processor fork: [
>             [ breakFlag ] whileFalse: [
>                 backgroundProcess := true.      "Process is now active "
>                     delay wait.
>                     ........................................."calling the
> GUI update methods displaying the measured values from the process"
>                    delay wait.
>             ].
>             backgroundProcess := false.         "Process is going to
> terminate "
>         ] at: Processor userPriority - 5
> Processor is an instance of ProcessScheduler.
> Something in our GUI update software wastes memory and over some days
> crashes the system. So the user has to stop the background display process
> when leaving the system and to restart it when coming back. We now want to
> automate this switching on and off of the GUI updates by checking the
> screensaver status of windows. Our wish is to check in each update cycle,
> whether the windows-screensaver is on, and depending on this status, to
> update the GUI display or not.
> Can anybody of you give us a hint, how to check, whether windows has
> switched of the desktop-display and displaying the screensaver, or is still
> displaying the desktop containing the squeak window?

Which OS? Windows, Mac, Linux, other?

One option is to find and fix your memory leak. I haven't tried this before
in Squeak (my applications crash much earlier than that :-P ), but I'd
probably start by doing something like:

Smalltalk collect: [ :each | (each isMemberOf: Class) ifTrue: [
    each name, ': ', each allInstances size, ' instances'

(there might be a #numInstances method on Behavior; I don't have an image
handy right now)

Inspecting the result after running your program for some time might give
some clues as to what is using up your memory.

You could write a custom screensaver in C, or maybe even in Squeak if you're
keen, and then that screensaver could somehow send a signal to your
application - maybe using TCP/IP, or maybe sending a signal to Squeak (can
Squeak capture POSIX signals?), or some other mechanism.


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