RFR: 8197812: (ref) Data race in Finalizer

[Peter Levart]

Hi Martin,

On 02/15/2018 06:47 AM, Martin Buchholz wrote:
> Embarrassed by my failure to take runFinalizersOnExit into account, I tried
> to redo the patch to be actually correct.

I think that your patch was correct the first time too, but in view of 
future removing the need for "pollFirst" from unfinalized list, the 
revised patch separates this logic entirely into the to-be-removed 
method so it is preferable.

>   http://cr.openjdk.java.net/~martin/webrevs/jdk/Finalizer-data-race/
> even though we may succeed in making runFinalizersOnExit go away, and I'm
> not planning to submit any time soon.
> The runFinalizersOnExit case needs different mechanics for removing
> elements from "unfinalized".
> The simple invariant is that you need to run the finalizer whenever an
> element is unlinked from unfinalized.
>

...and the check for "already been finalized" needs to be performed only 
in deregisterAndRunFinalizer as you did in new patch. Once 
runAllFinalizers is removed, this check and marking code could be 
removed too.

Although not strictly necessary for correctness, for the time being, it 
would be nice to be consistent in marking the Finalizer object "already 
finalized" in both places. Either set both next and prev to this or next 
to this and prev to null.

Regards, Peter