snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

balancer/rls/internal/adaptive/lookback.go

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+/*
+ *
+ * Copyright 2020 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package adaptive
+
+import "time"
+
+// lookback implements a moving sum over an int64 timeline.
+type lookback struct {
+	bins  int64         // Number of bins to use for lookback.
+	width time.Duration // Width of each bin.
+
+	head  int64   // Absolute bin index (time * bins / duration) of the current head bin.
+	total int64   // Sum over all the values in buf, within the lookback window behind head.
+	buf   []int64 // Ring buffer for keeping track of the sum elements.
+}
+
+// newLookback creates a new lookback for the given duration with a set number
+// of bins.
+func newLookback(bins int64, duration time.Duration) *lookback {
+	return &lookback{
+		bins:  bins,
+		width: duration / time.Duration(bins),
+		buf:   make([]int64, bins),
+	}
+}
+
+// add is used to increment the lookback sum.
+func (l *lookback) add(t time.Time, v int64) {
+	pos := l.advance(t)
+
+	if (l.head - pos) >= l.bins {
+		// Do not increment counters if pos is more than bins behind head.
+		return
+	}
+	l.buf[pos%l.bins] += v
+	l.total += v
+}
+
+// sum returns the sum of the lookback buffer at the given time or head,
+// whichever is greater.
+func (l *lookback) sum(t time.Time) int64 {
+	l.advance(t)
+	return l.total
+}
+
+// advance prepares the lookback buffer for calls to add() or sum() at time t.
+// If head is greater than t then the lookback buffer will be untouched. The
+// absolute bin index corresponding to t is returned. It will always be less
+// than or equal to head.
+func (l *lookback) advance(t time.Time) int64 {
+	ch := l.head                               // Current head bin index.
+	nh := t.UnixNano() / l.width.Nanoseconds() // New head bin index.
+
+	if nh <= ch {
+		// Either head unchanged or clock jitter (time has moved backwards). Do
+		// not advance.
+		return nh
+	}
+
+	jmax := min(l.bins, nh-ch)
+	for j := int64(0); j < jmax; j++ {
+		i := (ch + j + 1) % l.bins
+		l.total -= l.buf[i]
+		l.buf[i] = 0
+	}
+	l.head = nh
+	return nh
+}