RFR: 8254758: Change G1ServiceThread to be task based [v2]

[Stefan Johansson]

On Tue, 20 Oct 2020 06:46:29 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Thank you for the update regarding 1 and 2. As for `timeout=0`, it's not obvious to me how it will be resolved if there
> are multiple `timeout=0` tasks. Since there are no such tasks yet, I am fine with the current status. Ideally, please
> provide some doc on the behavior of `timeout=0` next to `virtual int64_t timeout_ms() = 0;`; sth like what's said for
> "negative" values.

I will update the comment. The way it will work is that each task is rescheduled using `os::elapsedTime()` and the
timeout. So a task with `timeout=0` would still be scheduled after a task with a time value smaller than what's
returned by `os::elapsedTime()`. Unless I'm overseeing something, this should be fine with multiple tasks as well.

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PR: https://git.openjdk.java.net/jdk/pull/734