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chore: import upstream snapshot with attribution
2026-07-13 12:31:17 +08:00

85 lines
2.6 KiB
Go

// Licensed to the LF AI & Data foundation under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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 utility
import (
"sync"
"time"
)
const numBuckets = 20 // max error ~5% (1/numBuckets)
// AverageRateCounter tracks the average rate of bytes over a sliding time window.
// Rate() returns total / window (bytes per second over the last window duration).
// It maintains a running total for O(1) Rate() queries.
// It is safe for concurrent use.
type AverageRateCounter struct {
mu sync.Mutex
window time.Duration
buckets []int64
total int64 // running sum of all bucket bytes
current int
lastTick time.Time
}
// NewAverageRateCounter creates a new rate counter with the given window duration.
// The window determines how far back in time to look when calculating the rate.
func NewAverageRateCounter(window time.Duration) *AverageRateCounter {
return &AverageRateCounter{
window: window,
buckets: make([]int64, numBuckets),
current: 0,
lastTick: time.Now(),
}
}
// Add adds the given number of bytes to the counter.
func (r *AverageRateCounter) Add(bytes int64) {
r.mu.Lock()
defer r.mu.Unlock()
now := time.Now()
r.advanceTime(now)
r.buckets[r.current] += bytes
r.total += bytes
}
// Rate returns the average rate in bytes per second over the last window duration.
func (r *AverageRateCounter) Rate() float64 {
r.mu.Lock()
defer r.mu.Unlock()
now := time.Now()
r.advanceTime(now)
return float64(r.total) / r.window.Seconds()
}
// advanceTime advances the current bucket if enough time has passed.
// When a bucket is evicted, its bytes are subtracted from the running total.
// Must be called with the lock held.
func (r *AverageRateCounter) advanceTime(now time.Time) {
bucketDuration := r.window / time.Duration(len(r.buckets))
for now.Sub(r.lastTick) >= bucketDuration {
r.current = (r.current + 1) % len(r.buckets)
r.total -= r.buckets[r.current]
r.buckets[r.current] = 0
r.lastTick = r.lastTick.Add(bucketDuration)
}
}