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+---- Thread: Why does this crash? (/showthread.php?tid=2011)
Why does this crash? - TerryRitchie - 09-18-2023
Can anyone explain why the code below crashes?
Sometimes the Y value gets as high as a few hundred, other times just barely past 10.
I would have chalked this up as running out of memory but the random crash points has me confused. The picture I'm using is attached below.
Code: (Select All)
OPTION _EXPLICIT
TYPE TYPE_PIXEL
hard AS LONG ' hardware image
soft AS LONG ' software image
ox AS INTEGER
oy AS INTEGER
x AS INTEGER
y AS INTEGER
xdir AS SINGLE
ydir AS SINGLE
END TYPE
DIM Pixel(1280, 720) AS TYPE_PIXEL
DIM Picture AS LONG
DIM x AS INTEGER
DIM y AS INTEGER
SCREEN _NEWIMAGE(1280, 720, 32)
Picture = _LOADIMAGE("picture.png", 32)
_SOURCE Picture
FOR y = 0 TO 719
FOR x = 0 TO 1279
Pixel(x, y).soft = _NEWIMAGE(1, 1, 32)
_DEST Pixel(x, y).soft
PSET (0, 0), POINT(x, y)
Pixel(x, y).hard = _COPYIMAGE(Pixel(x, y).soft, 33)
Pixel(x, y).ox = x
Pixel(x, y).oy = y
_DEST 0 ' temporarily print values to figure
PRINT x, y, Pixel(x, y).soft, Pixel(x, y).hard ' out why this crashes
NEXT x
NEXT y
RE: Why does this crash? - GareBear - 09-18-2023
TerryRitchie, could you comment out sections of code to narrow down what could be giving you problems when run?
RE: Why does this crash? - Dav - 09-18-2023
I'd guess it's all those Pixel(x, y).soft = _NewImage(1, 1, 32) images which aren't freed up? When I add a _FreeImage Pixel(x, y).soft at the end (just before the NEXT x) it doesn't crash.
- Dav
RE: Why does this crash? - TerryRitchie - 09-18-2023
(09-18-2023, 10:08 PM)Dav Wrote: I'd guess it's all those Pixel(x, y).soft = _NewImage(1, 1, 32) images which aren't freed up? When I add a _FreeImage Pixel(x, y).soft at the end (just before the NEXT x) it doesn't crash.Yep, you're right, how odd. However, I want to keep the software version of the pixel too for the demo I have in mind. Hmm, I'll play around with this.
- Dav
RE: Why does this crash? - TerryRitchie - 09-18-2023
Here is something else odd I'm noticing. The program seems to be crashing during a software surface redraw. See the image below.
RE: Why does this crash? - TerryRitchie - 09-18-2023
Ok, even if I try to create 1280x720 (921600) individual software images of 1x1 pixel with nothing else going on the program still crashes at random points. Something is not right here.
RE: Why does this crash? - mnrvovrfc - 09-18-2023
I have written a similar program and became convinced QB64PE doesn't like arrays of an user-defined type involved with long integers to be used for image handles.
On Slackel Linux, I wrote a program which was supposed to take a screenshot of the desktop at the time (clumsily with "scrot" command-line tool) and do a "meltdown" business like stuff from that cheap "Matrix" movie that keeps being recalled. Now I have to go find that program in my backups. It works now, because I was forced to allocate a separate array of long integers to hold the image handles, apart from an array of an UDT.
This contribution is actually useless in this thread but I had to voice it out.
RE: Why does this crash? - Dav - 09-18-2023
I can't open nearly that many 1x1 images either. Here's code I was playing with. When I increase the image size it crashes quicker too, so there is a memory limit I'm reaching. So It may be just the regular running out of memory issue. But why that limit is different for different runs I dunno, maybe an OS memory management thing? I'm just throwing out guesses....
- Dav
Code: (Select All)
Screen _NewImage(800, 600, 32)
Dim img&(500000)
For t& = 1 To 500000
Print t&
img&(t&) = _NewImage(1, 1, 32) 'increase pix size, it crashes quicker.
Next
RE: Why does this crash? - mnrvovrfc - 09-18-2023
I modified the above program to add a `_LIMIT 10000` inside the loop, and caused it to print every 1000 iterations. It gave up at about 300 thousand. But I needed to keep Firefox in memory and myself logged into this site, so...
RE: Why does this crash? - DSMan195276 - 09-19-2023
Unfortunately it's just a pretty straight forward bug in QB64, you can see it here.
Basically what's happening is that the program starts with a buffer that can hold 4096 images, and once you create more than that it will "resize" the buffer to be larger by another 4096. That resize process involves creating a new buffer, copying the contents, and then freeing the previous buffer. The code does attempt to update the pointers to images, hence the `update existing img pointers to new locations` comment, but unfortunately that's not good enough because the display thread is using `display_page` with no synchronization. The end result is that the display thread can end up reading from `display_page` when it still points to the old free'd buffer of images and that leads to it randomly blowing up.
I can't offer an actual fix at the moment beyond just avoiding that many images, but if you change `IMG_BUFFERSIZE` in `libqb.cpp` to be larger than the number of images your program will use then you can avoid the issue.