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fix bug in meter traversal logic #11

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merged 1 commit into from
Nov 8, 2019
Merged

fix bug in meter traversal logic #11

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15 changes: 9 additions & 6 deletions sweeper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,6 @@ func (sw *sweeper) update() {
timeMultiplier := float64(time.Second) / float64(tdiff)

// Calculate the bandwidth for all active meters.
newLen := len(sw.meters)
for i, m := range sw.meters[:sw.activeMeters] {
total := atomic.LoadUint64(&m.accumulator)
diff := total - m.snapshot.Total
Expand Down Expand Up @@ -147,8 +146,7 @@ func (sw *sweeper) update() {
// Reset the rate, keep the total.
m.registered = false
m.snapshot.Rate = 0
newLen--
sw.meters[i] = sw.meters[newLen]
sw.meters[i] = nil
}

// Re-add the total to all the newly active accumulators and set the snapshot to the total.
Expand All @@ -162,10 +160,15 @@ func (sw *sweeper) update() {
m.snapshot.Total = total
}

// trim the meter list
for i := newLen; i < len(sw.meters); i++ {
sw.meters[i] = nil
// compress and trim the meter list
var newLen int
for _, m := range sw.meters {
if m != nil {
sw.meters[newLen] = m
newLen++
}
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There's actually a trick to this:

newMeters := sw.meters[:0]
for _, m := range sw.meters {
    if m != nil {
        newMeters = append(newMeters, m)
    }
}
sw.meters = newMeters

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neat, but it probably generates the same code underneath :)

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do you want me to apply it? I am neutral either way and I usually prefer explicitness.

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actually, the trick might generate slower code because it has to do bounds checking.
Maybe the compiler is smart enough to elide it though, I wouldn't bet against it.

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The trick will do less bounds checking, IIRC. But I'm fine with this as it is.

}

sw.meters = sw.meters[:newLen]

// Finally, mark all meters still in the list as "active".
Expand Down