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// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:math' as math;
/// A throttling algorithm. This models the throttling after a bucket with
/// water dripping into it at the rate of 1 drop per replenish duration. If the
/// bucket has water when an operation is requested, 1 drop of water is removed
/// and the operation is performed. If not the operation is skipped. This
/// algorithm lets operations be performed in bursts without throttling, but
/// holds the overall average rate of operations to 1 per replenish duration.
class ThrottlingBucket {
final int bucketSize;
final Duration replenishDuration;
late int _drops = bucketSize;
late int _lastReplenish =;
ThrottlingBucket(this.bucketSize, this.replenishDuration);
bool removeDrop() {
if (_drops <= 0) {
return false;
} else {
return true;
void _checkReplenish() {
int now =;
int replenishMillis = replenishDuration.inMilliseconds;
if (_lastReplenish + replenishMillis >= now) {
int inc = (now - _lastReplenish) ~/ replenishMillis;
_drops = math.min(_drops + inc, bucketSize);
_lastReplenish += (replenishMillis * inc);