[OpenJDK 2D-Dev] RFR: 8240654 : ZGC can cause severe UI application repaint issues
kevin.rushforth at oracle.com
Wed Jun 10 22:57:38 UTC 2020
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.
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
> 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"
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