http://www.perlmonks.org?node_id=11132465


in reply to Re^2: weird case of memory corruption? -- Tk ProgressBar bugged?
in thread weird case of memory corruption?

I ran this code on v5.24 with good looking GUI, but with run time error:
Use of uninitialized value in numeric ge (>=) at C:\Users\xxxx\Documen
+ts\PerlProjects\Monks\node_id=11132441.pl line 31.
WARNING: $pid{ex1}{val} NOT FOUND!!
("ex1", { as => "temp", val => undef })

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I am a bit perplexed.

Update: I changed: 

$repeat->cancel() if  $pid{ex1}{val} >= 65;  # to the following...
$repeat->cancel() if  ($pid{ex1}{val} >= 65); 
and that seems to work better.

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Replies are listed 'Best First'.
Re^4: weird case of memory corruption? -- Tk ProgressBar bugged?
by Discipulus (Canon) on May 12, 2021 at 11:28 UTC
    Hello Marshall,

    this is exatcly the point: my code show the bug that happens only sometimes. Try to execute the code many times: 

    >perl tkprogressbar2.pl

Use of uninitialized value in numeric ge (>=) at tkprogressbar2.pl lin
+e 31.
WARNING: $pid{ex1}{val} NOT FOUND!!
("ex1", { as => "temp", val => undef })

>perl tkprogressbar2.pl

>perl tkprogressbar2.pl

>perl tkprogressbar2.pl

>perl tkprogressbar2.pl

Use of uninitialized value in numeric ge (>=) at tkprogressbar2.pl lin
+e 31.
WARNING: $pid{ex1}{val} NOT FOUND!!
("ex1", { as => "temp", val => undef })

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    L*

    There are no rules, there are no thumbs..
    Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.
[reply]
[d/l]
      OK. Your point is accepted and verified by me on Perl v5.24.

      I actually saw this in my testing, but I couldn't believe my own eyes!
      The exact same source code can produce different results when run more than once.

      I am flabbergasted! This is true, but I don't know why or how?

      More Info:
      Updating a Windows GUI is an extremely expensive operation.
      If you have a loop that will do say 10,000 operations, and you want to show progress via a percent or a progress bar, calculate whether or not the progress bar will move before you update the GUI's value - do this at most 100 times (each one percent for a 100% bar) and probably less than that! The difference in performance between calling the GUI 10,000 times vs 100 times is astonishing!

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