RFR: 8079315: UseCondCardMark broken in conjunction with CMS precleaning

Vitaly Davidovich vitalyd at gmail.com
Tue May 5 19:54:15 UTC 2015


I'm intrigued - what hardware delays writes in the seconds?

sent from my phone
On May 5, 2015 3:34 PM, "Andrew Haley" <aph at redhat.com> wrote:

> On 05/05/2015 05:53 PM, Aleksey Shipilev wrote:
> >
> > But I am suspicious about the whole interaction between mutator and
> collector. Cautiously speaking, every time I see a conditional update in a
> concurrent code, I expect some form of atomic CAS that provides a global
> order w.r.t. the particular memory location.
> >
> > What exactly happens when collector transits card to "clean"? How does
> the mutator sees the proper "clean" value for the card mark? Can it miss
> the card mark update with UseCondCardMark because it saw the "outdated"
> card mark value?
>
> That's what worries me too.  But my attitude is coloured by some of
> the hardware I've been using recently, where some stale values in
> cache I've seen can only be explained by missing updates that happened
> not microseconds nor even milliseconds, but actual seconds ago.  And
> so I know this: whatever is not forbidden will happen, and more often
> than I expect!
>
> Andrew.
>
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