[OpenJDK 2D-Dev] RFR: 8240654 : ZGC can cause severe UI application repaint issues

Philip Race philip.race at oracle.com
Thu Jun 11 14:33:34 UTC 2020

On 6/11/20, 1:57 AM, Jayathirth D v wrote:
> Hi Phil,
> I tried tested the fix in my Windows 10 machine with Intel integrated 
> UHD Graphics 620.
> LargeWindowPaintTest.java passes with/without fix in my machine.
> AlphaPrintTest.java without fix just opens up blank frame without any 
> instructions and with fix it shows instructions for the test.
> Is this expected behaviour?

I guess this is a conseqeuence of the on-screen bug ! Which in contrast 
to the LargeWindowPaintTest affects you.

Without the fix the window is too big and you have an intel chip so you 
are going through the GDI path.
> AlphaPrintTest.java with fix when it shows instructions if I click on 
> Pass(Since I don’t have printer right now) it doesn’t pass/close the 
> window. Only after I click on Print button and then close print dialog 
> it allows me to click on Pass button.
Well .. perhaps I should add an @requires printer on this test ?
But can't you print to file using Windows built in print to pdf ?
> Also how does these tests behave in our internal CI machines?
The printing one is manual so it is never going to pass there.

> Thanks,
> Jay
>> On 11-Jun-2020, at 2:18 AM, Philip Race <philip.race at oracle.com 
>> <mailto:philip.race at oracle.com>> 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 
>> chunks  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.
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