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<?php
namespace Aws\Retry;
/**
* @internal
*/
class RateLimiter
{
// User-configurable constants
private $beta;
private $minCapacity;
private $minFillRate;
private $scaleConstant;
private $smooth;
// Optional callable time provider
private $timeProvider;
// Pre-set state variables
private $currentCapacity = 0;
private $enabled = false;
private $lastMaxRate = 0;
private $measuredTxRate = 0;
private $requestCount = 0;
// Other state variables
private $fillRate;
private $lastThrottleTime;
private $lastTimestamp;
private $lastTxRateBucket;
private $maxCapacity;
private $timeWindow;
public function __construct($options = [])
{
$this->beta = isset($options['beta'])
? $options['beta']
: 0.7;
$this->minCapacity = isset($options['min_capacity'])
? $options['min_capacity']
: 1;
$this->minFillRate = isset($options['min_fill_rate'])
? $options['min_fill_rate']
: 0.5;
$this->scaleConstant = isset($options['scale_constant'])
? $options['scale_constant']
: 0.4;
$this->smooth = isset($options['smooth'])
? $options['smooth']
: 0.8;
$this->timeProvider = isset($options['time_provider'])
? $options['time_provider']
: null;
$this->lastTxRateBucket = floor($this->time());
$this->lastThrottleTime = $this->time();
}
public function isEnabled()
{
return $this->enabled;
}
public function getSendToken()
{
$this->acquireToken(1);
}
public function updateSendingRate($isThrottled)
{
$this->updateMeasuredRate();
if ($isThrottled) {
if (!$this->isEnabled()) {
$rateToUse = $this->measuredTxRate;
} else {
$rateToUse = min($this->measuredTxRate, $this->fillRate);
}
$this->lastMaxRate = $rateToUse;
$this->calculateTimeWindow();
$this->lastThrottleTime = $this->time();
$calculatedRate = $this->cubicThrottle($rateToUse);
$this->enableTokenBucket();
} else {
$this->calculateTimeWindow();
$calculatedRate = $this->cubicSuccess($this->time());
}
$newRate = min($calculatedRate, 2 * $this->measuredTxRate);
$this->updateTokenBucketRate($newRate);
return $newRate;
}
private function acquireToken($amount)
{
if (!$this->enabled) {
return true;
}
$this->refillTokenBucket();
if ($amount > $this->currentCapacity) {
usleep(1000000 * ($amount - $this->currentCapacity) / $this->fillRate);
}
$this->currentCapacity -= $amount;
return true;
}
private function calculateTimeWindow()
{
$this->timeWindow = pow(($this->lastMaxRate * (1 - $this->beta) / $this->scaleConstant), 0.333);
}
private function cubicSuccess($timestamp)
{
$dt = $timestamp - $this->lastThrottleTime;
return $this->scaleConstant * pow($dt - $this->timeWindow, 3) + $this->lastMaxRate;
}
private function cubicThrottle($rateToUse)
{
return $rateToUse * $this->beta;
}
private function enableTokenBucket()
{
$this->enabled = true;
}
private function refillTokenBucket()
{
$timestamp = $this->time();
if (!isset($this->lastTimestamp)) {
$this->lastTimestamp = $timestamp;
return;
}
$fillAmount = ($timestamp - $this->lastTimestamp) * $this->fillRate;
$this->currentCapacity = $this->currentCapacity + $fillAmount;
if (!is_null($this->maxCapacity)) {
$this->currentCapacity = min(
$this->maxCapacity,
$this->currentCapacity
);
}
$this->lastTimestamp = $timestamp;
}
private function time()
{
if (is_callable($this->timeProvider)) {
$provider = $this->timeProvider;
$time = $provider();
return $time;
}
return microtime(true);
}
private function updateMeasuredRate()
{
$timestamp = $this->time();
$timeBucket = floor(round($timestamp, 3) * 2) / 2;
$this->requestCount++;
if ($timeBucket > $this->lastTxRateBucket) {
$currentRate = $this->requestCount / ($timeBucket - $this->lastTxRateBucket);
$this->measuredTxRate = ($currentRate * $this->smooth)
+ ($this->measuredTxRate * (1 - $this->smooth));
$this->requestCount = 0;
$this->lastTxRateBucket = $timeBucket;
}
}
private function updateTokenBucketRate($newRps)
{
$this->refillTokenBucket();
$this->fillRate = max($newRps, $this->minFillRate);
$this->maxCapacity = max($newRps, $this->minCapacity);
$this->currentCapacity = min($this->currentCapacity, $this->maxCapacity);
}
}
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