Threads with TBItmap, TJpegImage, TGraphics32

[xor2]

Hello,

I have a procedure which performs some operation on jpg file (like transformations, etc).

I am;

- reading pixel from canvas
ACanvas.Pixels[X,Y];
- drawing on canvas
Bitmap.Canvas.Draw(0,0,jpg);
- assign bitmap from another source
Bitmap.Assign(LBitmapPomn);

The problem is that when i Run this procedure in a one thread everything is perfectly allright. I don't have memory leaks nor I have increased number of GDI objects and
the memory in the process manager varies from 50 to 100 mb and after this it returns to its default value.

The problem starts when i want to run this procedure in 4 threads. I have memory leaks. Memory inscreased to 1.7 gb, gdi +500 objects and so on..

I know only that Graphics32 component is thread-safe.
What about TBitmap, TJpegImage?
Which operation with this classes I should "Lock", should I lock?

Could the memory leak occur because of using these components?

How Can i fix my code?

Thanks for help in advance..

 

[whosrdaddy]

as you noticed, the VCL is not threadsafe. and yes you must lock the canvas before manipulating it (writing AND reading)

some guidelines:

canvas manipulations: main thread
calculations : you can use other threads, don't for get to synchronize with the main thread and between other calculation threads.

some more info:

http://www.drbob42.com/uk-bug/hood-04.htm

/Daddy

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[xor2]

Thank you for your post and the link which helped me understood how I could use Synchronize method with canvas manipulations.

By the way, Are you familiar with Graphics32?
Do you know if Graphics32's canvas is thread-safe?

 

[Duoas]

I believe it is, but there may be caveats.

Make sure you do some reading and heavy testing.

http://graphics32.org/wiki/pub/page/Main/HomePage

Good luck!