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<?php
/*
* Copyright 2014 Google Inc.
*
* 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.
*/
/**
* A task runner with exponential backoff support.
*
* @see https://developers.google.com/drive/web/handle-errors#implementing_exponential_backoff
*/
class Google_Task_Runner
{
const TASK_RETRY_NEVER = 0;
const TASK_RETRY_ONCE = 1;
const TASK_RETRY_ALWAYS = -1;
/**
* @var integer $maxDelay The max time (in seconds) to wait before a retry.
*/
private $maxDelay = 60;
/**
* @var integer $delay The previous delay from which the next is calculated.
*/
private $delay = 1;
/**
* @var integer $factor The base number for the exponential back off.
*/
private $factor = 2;
/**
* @var float $jitter A random number between -$jitter and $jitter will be
* added to $factor on each iteration to allow for a better distribution of
* retries.
*/
private $jitter = 0.5;
/**
* @var integer $attempts The number of attempts that have been tried so far.
*/
private $attempts = 0;
/**
* @var integer $maxAttempts The max number of attempts allowed.
*/
private $maxAttempts = 1;
/**
* @var callable $action The task to run and possibly retry.
*/
private $action;
/**
* @var array $arguments The task arguments.
*/
private $arguments;
/**
* @var array $retryMap Map of errors with retry counts.
*/
protected $retryMap = [
'500' => self::TASK_RETRY_ALWAYS,
'503' => self::TASK_RETRY_ALWAYS,
'rateLimitExceeded' => self::TASK_RETRY_ALWAYS,
'userRateLimitExceeded' => self::TASK_RETRY_ALWAYS,
6 => self::TASK_RETRY_ALWAYS, // CURLE_COULDNT_RESOLVE_HOST
7 => self::TASK_RETRY_ALWAYS, // CURLE_COULDNT_CONNECT
28 => self::TASK_RETRY_ALWAYS, // CURLE_OPERATION_TIMEOUTED
35 => self::TASK_RETRY_ALWAYS, // CURLE_SSL_CONNECT_ERROR
52 => self::TASK_RETRY_ALWAYS // CURLE_GOT_NOTHING
];
/**
* Creates a new task runner with exponential backoff support.
*
* @param array $config The task runner config
* @param string $name The name of the current task (used for logging)
* @param callable $action The task to run and possibly retry
* @param array $arguments The task arguments
* @throws Google_Task_Exception when misconfigured
*/
public function __construct(
$config,
$name,
$action,
array $arguments = array()
) {
if (isset($config['initial_delay'])) {
if ($config['initial_delay'] < 0) {
throw new Google_Task_Exception(
'Task configuration `initial_delay` must not be negative.'
);
}
$this->delay = $config['initial_delay'];
}
if (isset($config['max_delay'])) {
if ($config['max_delay'] <= 0) {
throw new Google_Task_Exception(
'Task configuration `max_delay` must be greater than 0.'
);
}
$this->maxDelay = $config['max_delay'];
}
if (isset($config['factor'])) {
if ($config['factor'] <= 0) {
throw new Google_Task_Exception(
'Task configuration `factor` must be greater than 0.'
);
}
$this->factor = $config['factor'];
}
if (isset($config['jitter'])) {
if ($config['jitter'] <= 0) {
throw new Google_Task_Exception(
'Task configuration `jitter` must be greater than 0.'
);
}
$this->jitter = $config['jitter'];
}
if (isset($config['retries'])) {
if ($config['retries'] < 0) {
throw new Google_Task_Exception(
'Task configuration `retries` must not be negative.'
);
}
$this->maxAttempts += $config['retries'];
}
if (!is_callable($action)) {
throw new Google_Task_Exception(
'Task argument `$action` must be a valid callable.'
);
}
$this->action = $action;
$this->arguments = $arguments;
}
/**
* Checks if a retry can be attempted.
*
* @return boolean
*/
public function canAttempt()
{
return $this->attempts < $this->maxAttempts;
}
/**
* Runs the task and (if applicable) automatically retries when errors occur.
*
* @return mixed
* @throws Google_Task_Retryable on failure when no retries are available.
*/
public function run()
{
while ($this->attempt()) {
try {
return call_user_func_array($this->action, $this->arguments);
} catch (Google_Service_Exception $exception) {
$allowedRetries = $this->allowedRetries(
$exception->getCode(),
$exception->getErrors()
);
if (!$this->canAttempt() || !$allowedRetries) {
throw $exception;
}
if ($allowedRetries > 0) {
$this->maxAttempts = min(
$this->maxAttempts,
$this->attempts + $allowedRetries
);
}
}
}
}
/**
* Runs a task once, if possible. This is useful for bypassing the `run()`
* loop.
*
* NOTE: If this is not the first attempt, this function will sleep in
* accordance to the backoff configurations before running the task.
*
* @return boolean
*/
public function attempt()
{
if (!$this->canAttempt()) {
return false;
}
if ($this->attempts > 0) {
$this->backOff();
}
$this->attempts++;
return true;
}
/**
* Sleeps in accordance to the backoff configurations.
*/
private function backOff()
{
$delay = $this->getDelay();
usleep($delay * 1000000);
}
/**
* Gets the delay (in seconds) for the current backoff period.
*
* @return float
*/
private function getDelay()
{
$jitter = $this->getJitter();
$factor = $this->attempts > 1 ? $this->factor + $jitter : 1 + abs($jitter);
return $this->delay = min($this->maxDelay, $this->delay * $factor);
}
/**
* Gets the current jitter (random number between -$this->jitter and
* $this->jitter).
*
* @return float
*/
private function getJitter()
{
return $this->jitter * 2 * mt_rand() / mt_getrandmax() - $this->jitter;
}
/**
* Gets the number of times the associated task can be retried.
*
* NOTE: -1 is returned if the task can be retried indefinitely
*
* @return integer
*/
public function allowedRetries($code, $errors = array())
{
if (isset($this->retryMap[$code])) {
return $this->retryMap[$code];
}
if (
!empty($errors) &&
isset($errors[0]['reason'], $this->retryMap[$errors[0]['reason']])
) {
return $this->retryMap[$errors[0]['reason']];
}
return 0;
}
public function setRetryMap($retryMap)
{
$this->retryMap = $retryMap;
}
}
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