+1
Just curious about what performance degradation we will have in the worst case.
On 6/10/20 3:57 pm, Kevin Rushforth wrote:
+1
Code changes look good.
I verified that the bug happens on my Windows 10 laptop with SwingSet2 and with
the LargeWindowPaintTest without the patch, and everything looks good with the
patch.
-- Kevin
On 6/10/2020 1:48 PM, Philip Race wrote:
Bug: https://bugs.openjdk.java.net/browse/JDK-8240654
Webrev: http://cr.openjdk.java.net/~prr/8240654/index.html
This is for JDK 15 so review ASAP please since RDP 1 and the test cycle are
looming.
This is not a fix for a JDK bug. It is a bunch of workarounds for a Microsoft
Windows bug affecting
GDI in the context of ZGC (http://openjdk.java.net/jeps/333).
Some extra details about the Windows bug at the end, but first the technical
details of the fix.
With ZGC's memory allocation requirement of reserving memory in 2Mb chunksÂ
some Windows GDI
functions, mostly involving some bitmaps APIs may return a failure code (ie
fail!)
This typically occurs when Java heap memory is used for a Java image and then
in a JNI
call we use GetPrimitiveArrayCritical so that Java heap allocated memory is
passed to a GDI
function AND the Java heap memory spans one of the 2Mb boundaries.
This is very easy to trigger in almost any Java UI app if the window is of a
large enough (ie typical) size.
NB: if you have an Nvidia or ATI card, then you won't see it, because the D3D
pipeline doesn't
call the affected method but if you have an Intel chip as do 90% (?) of laptops
you will see it.
There are also several other places we found that are affected. Printing is the
other one
somewhat easy to trigger. The others : custom cursors and tray icons are less
common.
The painful thing here is that there is no definitive list (a list of the known
ones is below) of
affected Windows GDI APIs and we are just hunting around our code trying to see
where it
might be side-swiped by this bug.
The basic approach in these workarounds is that for cases where performance
does not matter we now copy
and for cases where performance does matter or larger amounts of memory is
involved we check if
the return value of the GDI function indicates failure and then re-try with a
copy of the heap memory.
Unless GDI was randomly failing already (unlikely) this should be a no-risk
solution in the high profile cases.
We have done performance measurements on the important screen case and the
failures
happen fast so the penalty is then in the re-try which is only if ZGC is
enabled.
Always copying the memory is slower (and memcpy is the slow operation) than an
alternative approach
that "knows" about the memory allocation of ZGC but this coupling and the
complexity seem like they aren't
worth it since I haven't seen any visible performance consequence. That can be
revisited
some day if need be, but for now we have correctness which is the key as well
as sufficient performance.
I've created an automated test for the most important on-screen case.
Also a manual printing test case which invokes ZGC is provided since there we
also only
conditionally copy. In the other cases we now always copy so existing test
cases should over those.
There is some clean up in this fix - one completely unused (provably so because
it was #if'd out)
JNI method in awt_PrintJob.cpp is removed since it had code that looked like it
needed a workaround,
which would be somewhat of a waste of effort.
the doPrintBand code and its callee bitsToDevice has code I think we can remove
too since
I don't see how it ever gets executed (the top down case for browserPrint ==
true) but
I think I'll save that for a P4 follow-on since it does nothing that would be
affected by this
Windows bug.
One oddity is the in the printing case I observed that some times the rendering
is performed
even if an error code is returned. I don't know why, but in code we can't tell
that it was actually
rendered and in any case there is no harm in repeating the call with copied
memory.
We are right before the JDK15 stabilisation fork and this fix needs to go there
and will
but the webrev is against jdk/client simply because jdk15 does not exist yet !
Please test and review ASAP.
About the bug:
Microsoft has acknowleged the bug and will publish a knowledge base article
about it
but a fix may show up only in a future version of Windows. Not, it seems, any
time soon.
Below is a list of potentially affected GDI APIs. Per microsoft whether it
actually manifests in
any specific case depends on "branching"
https://docs.microsoft.com/en-us/previous-versions/windows/desktop/wcs/checkbitmapbits
https://docs.microsoft.com/en-us/previous-versions/windows/desktop/wcs/createcolortransform
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-setdibitstodevice
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-stretchdibits
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getbitmapbits
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-createdibitmap
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-createdibsection
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-polydraw
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-drawescape
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-createbitmap
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-setbitmapbits
https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getdibits
-phil.
--
Best regards, Sergey.
