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<?php
/**
* Copyright 2016 Google Inc. All Rights Reserved.
*
* 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.
*/
namespace Google\Cloud\Core;
/**
* Exponential backoff implementation.
*/
class ExponentialBackoff
{
const MAX_DELAY_MICROSECONDS = 60000000;
/**
* @var int
*/
private $retries;
/**
* @var callable|null
*/
private $retryFunction;
/**
* @var callable
*/
private $delayFunction;
/**
* @var callable|null
*/
private $calcDelayFunction;
/**
* @param int $retries [optional] Number of retries for a failed request.
* @param callable $retryFunction [optional] returns bool for whether or not to retry
*/
public function __construct($retries = null, callable $retryFunction = null)
{
$this->retries = $retries !== null ? (int) $retries : 3;
$this->retryFunction = $retryFunction;
// @todo revisit this approach
// @codeCoverageIgnoreStart
$this->delayFunction = static function ($delay) {
usleep($delay);
};
// @codeCoverageIgnoreEnd
}
/**
* Executes the retry process.
*
* @param callable $function
* @param array $arguments [optional]
* @return mixed
* @throws \Exception The last exception caught while retrying.
*/
public function execute(callable $function, array $arguments = [])
{
$delayFunction = $this->delayFunction;
$calcDelayFunction = $this->calcDelayFunction ?: [$this, 'calculateDelay'];
$retryAttempt = 0;
$exception = null;
while (true) {
try {
return call_user_func_array($function, $arguments);
} catch (\Exception $exception) {
if ($this->retryFunction) {
if (!call_user_func($this->retryFunction, $exception, $retryAttempt)) {
throw $exception;
}
}
if ($retryAttempt >= $this->retries) {
break;
}
$delayFunction($calcDelayFunction($retryAttempt));
$retryAttempt++;
}
}
throw $exception;
}
/**
* If not set, defaults to using `usleep`.
*
* @param callable $delayFunction
* @return void
*/
public function setDelayFunction(callable $delayFunction)
{
$this->delayFunction = $delayFunction;
}
/**
* If not set, defaults to using
* {@see Google\Cloud\Core\ExponentialBackoff::calculateDelay()}.
*
* @param callable $calcDelayFunction
* @return void
*/
public function setCalcDelayFunction(callable $calcDelayFunction)
{
$this->calcDelayFunction = $calcDelayFunction;
}
/**
* Calculates exponential delay.
*
* @param int $attempt The attempt number used to calculate the delay.
* @return int
*/
public static function calculateDelay($attempt)
{
return min(
mt_rand(0, 1000000) + (pow(2, $attempt) * 1000000),
self::MAX_DELAY_MICROSECONDS
);
}
}
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