[OpenJDK 2D-Dev] [9] Review Request: 8080847 Copying of overlapping memory should be improved in java2d

Jim Graham james.graham at oracle.com
Mon May 25 19:16:13 UTC 2015

I don't recall if we ever promised that this case would work without 
aliasing issues.  I know that we went out of our way in the copyArea 
method to prevent the aliasing issue, doing the blits piecemeal so that 
they don't interfere with each other.  Further, while it may be easy 
enough to just call memmove to have the libraray do this for us in the 
IsoBlit case, other cases that don't fall into the IsoBlit macro will 
not be similarly protected.  In particular, if you specify an alpha 
value, you will not get this protection (at least not without a huge 
amount of work to overhaul the entire DrawImage pipeline).

I would say that this would be OK if we planned to make this promise 
about drawImage across all image formats and composition modes, but that 
would be a far more complicated fix.  Until then, we should not open 
this can of worms by modifying this one specific Blit case...


On 5/25/2015 5:35 AM, Sergey Bylokhov wrote:
> Hello.
> Please review the fix forjdk9.
> I found this issue during code review of another task, related to
> performance.
> The sample code below will call the IsomorphicCopy method which call
> memcpy on the overlapping memory(this is the simplest example)
>       BufferedImage img = new BufferedImage(100, 100,
> BufferedImage.TYPE_INT_ARGB_PRE);
>       Graphics2D g = img.createGraphics();
>       g.setComposite(AlphaComposite.Src);
>       g.drawImage(img, 0, 0, null);
>       g.dispose();
> http://linux.die.net/man/3/memcpy
> "The memcpy() function copies n bytes from memory area src to memory
> area dest. The memory areas must not overlap. Use memmove(3) if the
> memory areas do overlap"
> I can confirm this bug using valgrind and a program above:
> command:
> valgrind --smc-check=all --tool=memcheck --leak-check=full -v
> ./9/client/build/linux-x86_64-normal-server-fastdebug/images/jdk/bin/java -Xint
> Main
> output:
> ==60975== Source and destination overlap in memcpy(0xe1b8b4d8,
> 0xe1b8b4d8, 400)
> ==60975== at 0x4C2F71C: memcpy@@GLIBC_2.14 (in
> /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==60975== by 0x1E0F504D: AnyIntIsomorphicCopy (in
> /moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)
> ==60975== by 0x1E0F5DE8: Java_sun_java2d_loops_Blit_Blit (in
> /moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)
> Bug: https://bugs.openjdk.java.net/browse/JDK-8080847
> Webrev can be found at: http://cr.openjdk.java.net/~serb/8080847/webrev.00

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