RFR: 8209163: SA: Show Object Histogram asserts with ZGC

[JC Beyler]

Hi Per,

I do not know this code but your need to call heapIterationFractionUpdate
seems to be a code smell that something else could be fixed, no?

Your webrev looks fine to me if I ignore the code smell that comes from
having to call the update call:

When I look at
src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/HSDB.java, the reason
it requires that first call is, like you said, that the frame is created
only at the first heapIterationFractionUpdate. However, could we not test
frame and if it is not created, don't try to remove it?

Thanks,
Jc

On Wed, Sep 12, 2018 at 1:25 AM Per Liden <per.liden at oracle.com> wrote:

> This patch avoids an assertion, and instead prints a warning, when
> trying to show the "Object Histogram" when using ZGC. I also had to add
> a call to heapIterationFractionUpdate() so that the update progress
> frame is properly created, even when there are not heap regions to walk
> over. Without this, you only get a call to heapIterationCompleted(),
> with a null frame, which throws a NullPointerException. Always making a
> call to heapIterationFractionUpdate(0.0) in the prologue avoids this by
> making sure we always created the frame, even if no more fraction
> updates will happen.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8209163
> Webrev: http://cr.openjdk.java.net/~pliden/8209163/webrev.0
>
> /Per
>


-- 

Thanks,
Jc
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