RFR: 8253478: (se) epoll Selector should use eventfd for wakeup instead of pipe

[Brian Burkhalter]

On Thu, 14 Jan 2021 17:00:33 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Please review this change which modifies the Linux `epoll(7)`-based `Selector` to use `eventfd(2)` instead of `pipe(2)` in its wakeup mechanism. The change passes all tier 1-tier 3 tests on Linux. Based on rudimentary testing, there does not appear to be any appreciable change in performance. One improvement however is that only one file descriptor instead of two is used for the wakeup. No test is included as the code is covered well by existing tests.
>
> @bplb I think it's too premature to ask us to review this until you have some performance data. Do we have any existing micros for wakeup?

Yes. I have one based on the Wakeup test but it is rather ugly.

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PR: https://git.openjdk.java.net/jdk/pull/2082