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perf: Reduce loops when cleaning queue in BroadcastHub #1628

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Merged
He-Pin merged 1 commit into from
Dec 30, 2024
Merged

perf: Reduce loops when cleaning queue in BroadcastHub #1628

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19 changes: 15 additions & 4 deletions stream/src/main/scala/org/apache/pekko/stream/scaladsl/Hub.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -605,10 +605,7 @@ private[pekko] class BroadcastHub[T](startAfterNrOfConsumers: Int, bufferSize: I
else if (head != finalOffset) {
// If our final consumer goes away, we roll forward the buffer so a subsequent consumer does not
// see the already consumed elements. This feature is quite handy.
while (head != finalOffset) {
queue(head & Mask) = null
head += 1
}
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@He-Pin He-Pin Dec 28, 2024

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Which can loop many times

cleanQueueInRange(head, finalOffset)
head = finalOffset
tryPull()
}
Expand All @@ -617,6 +614,20 @@ private[pekko] class BroadcastHub[T](startAfterNrOfConsumers: Int, bufferSize: I
}
}

private def cleanQueueInRange(headOffset: Int, upToOffset: Int): Unit = {
// We need to clean the queue from headOffset to upToOffset
if (headOffset != upToOffset) {
val startIdx = headOffset & Mask
val endIdx = upToOffset & Mask
if (startIdx <= endIdx) {
java.util.Arrays.fill(queue, startIdx, endIdx, null)
} else {
java.util.Arrays.fill(queue, startIdx, queue.length, null)
java.util.Arrays.fill(queue, 0, endIdx, null)
}
}
}

// Producer API
// We are full if the distance between the slowest (known) consumer and the fastest (known) consumer is
// the buffer size. We must wait until the slowest either advances, or cancels.
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