RFR: 8280041: Retry loop issues in java.io.ClassCache [v4]

[Aleksey Shipilev]

On Tue, 25 Jan 2022 16:12:11 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> > This looks good, although I don't know whether the additional check for strongReferent != null is needed in clearStrong(). This is all racy code and you have already got a non-null return from getStrong() in case you are calling clearStrong()...
> 
> This seems like a standard thing to do to avoid multi-threaded write contention under the race. By the time one thread calls `clearStrong`, some other thread might have already cleared it, and we don't have to clear again. Granted, that is a micro-optimization, but I'd like to avoid surprises on this path :)

Actually, the window after the first `strongVal != null` check is not that large that a second null check would matter. Dropped the null check in `clearStrong` for simplicity. (IIRC, it mattered a bit in prior internal iterations of my patch).

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PR: https://git.openjdk.java.net/jdk/pull/7092