Runner.php 6.34 KB
Newer Older
Ad Schellevis's avatar
Ad Schellevis committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257
<?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.
 */

if (!class_exists('Google_Client')) {
  require_once dirname(__FILE__) . '/../autoload.php';
}

/**
 * A task runner with exponential backoff support.
 *
 * @see https://developers.google.com/drive/web/handle-errors#implementing_exponential_backoff
 */
class Google_Task_Runner
{
  /**
   * @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 Google_Client $client The current API client.
   */
  private $client;

  /**
   * @var string $name The name of the current task (used for logging).
   */
  private $name;
  /**
   * @var callable $action The task to run and possibly retry.
   */
  private $action;
  /**
   * @var array $arguments The task arguments.
   */
  private $arguments;

  /**
   * Creates a new task runner with exponential backoff support.
   *
   * @param Google_Client $client The current API client
   * @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(
      Google_Client $client,
      $name,
      $action,
      array $arguments = array()
  ) {
    $config = (array) $client->getClassConfig('Google_Task_Runner');

    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->name = $name;
    $this->client = $client;
    $this->action = $action;
    $this->arguments = $arguments;
  }

  /**
   * Checks if a retry can be attempted.
   *
   * @return boolean
   */
  public function canAttmpt()
  {
    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_Task_Retryable $exception) {
        $allowedRetries = $exception->allowedRetries();

        if (!$this->canAttmpt() || !$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->canAttmpt()) {
      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();

    $this->client->getLogger()->debug(
        'Retrying task with backoff',
        array(
            'request' => $this->name,
            'retry' => $this->attempts,
            'backoff_seconds' => $delay
        )
    );

    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;
  }
}