[9/N][VQueues] Ensure the scheduler's internal clock wheel is synchronized with eligibility_at #4057
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AhmedSoliman
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…nized with eligibility_at This changeset makes sure that we have a reliable datum point that's shared between the delayed queue internal timer wheel and the scheduler. Additionally, it ensures that the scheduler can create `Instant` values that are synchronized with the datum point acquired from UniqueTimestamp. This fixes the issue introduced in changeset 6e65909 where we would become eligible slightly before the actual eligibility time, causing supurious rescheduling.
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tillrohrmann
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Thanks a lot for fixing the handling of delayed invocations @AhmedSoliman. The changes look good to me. I had a question about the need to set the start value of the DelayQueue explicitly.
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| // Makes sure we use the same clock datum for the internal timer wheel and for our | ||
| // own eligibility checks. | ||
| let start = datum.origin_instant(); | ||
| let delayed_eligibility = DelayQueue::new(start); |
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I don't fully understand why it is strictly required that the DelayQueue has the same start as the datum.origin_instant(). It seems as if the DelayQueue uses the start value for calculating offsets for internal purposes.
Isn't it enough that we are using the same clock (Tokio's) and insert_at and reset_at with concrete instants instead of durations to make the scheduling work reliably? Or differently asked, what would not work if we didn't set the start value of the DelayQueue.
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This changeset makes sure that we have a reliable datum point that's shared between the delayed queue internal timer wheel and the scheduler.
Additionally, it ensures that the scheduler can create
Instantvalues that are synchronized with the datum point acquired from UniqueTimestamp.This fixes the issue introduced in changeset 6e65909 where we would become eligible slightly before the actual eligibility time, causing supurious rescheduling.
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