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Introduce Backoff duration implementation with exponential strategy
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‎src/ExponentialBackoff.php‎

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<?php
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namespace ipl\Stdlib;
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use Exception;
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use LogicException;
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class ExponentialBackoff
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{
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/** @var int The minimum wait time for each retry in ms */
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protected $min;
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/** @var int The maximum wait time for each retry in ms */
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protected $max;
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/** @var int Number of retries to be performed before giving up */
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protected $retries;
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/** @var ?int The previous used retry wait time */
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protected $previousWaitTime;
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/**
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* Create a backoff duration with exponential strategy implementation.
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*
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* @param int $retries The number of retries to be used before given up.
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* @param int $min The minimum wait time to be used in milliseconds.
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* @param int $max The maximum wait time to be used in milliseconds.
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*/
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public function __construct(int $retries = 1, int $min = 0, int $max = 0)
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{
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$this->retries = $retries;
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$this->setMin($min);
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$this->setMax($max);
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}
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/**
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* Get the minimum wait time
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*
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* @return int
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*/
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public function getMin(): int
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{
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return $this->min;
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}
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/**
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* Set the minimum wait time
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*
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* @param int $min
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*
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* @return $this
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*/
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public function setMin(int $min): self
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{
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if ($min <= 0) {
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$min = 100; // Default minimum wait time 100 ms
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}
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$this->min = $min;
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return $this;
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}
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/**
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* Get the maximum wait time
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*
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* @return int
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*/
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public function getMax(): int
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{
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return $this->max;
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}
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/**
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* Set the maximum wait time
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*
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* @param int $max
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*
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* @return $this
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* @throws LogicException When the configured minimum wait time is greater than the maximum wait time
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*/
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public function setMax(int $max): self
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{
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if ($max <= 0) {
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$max = 10000; // Default max wait time 10 seconds
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}
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$this->max = $max;
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if ($this->min > $this->max) {
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throw new LogicException('Max must be larger than min');
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}
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return $this;
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}
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/**
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* Get the configured number of retries
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*
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* @return int
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*/
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public function getRetries(): int
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{
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return $this->retries;
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}
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/**
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* Set number of retries to be used
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*
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* @param int $retries
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*
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* @return $this
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*/
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public function setRetries(int $retries): self
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{
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$this->retries = $retries;
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return $this;
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}
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/**
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* Get a new wait time for the given attempt
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*
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* If the given attempt is the initial one, the min wait time is used. For all subsequent requests,
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* the previous wait time is simply multiplied by 2.
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*
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* @param int $attempt
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*
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* @return int
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*/
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public function getWaitTime(int $attempt): int
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{
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if ($attempt === 0) {
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$this->previousWaitTime = null;
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}
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if ($this->previousWaitTime >= $this->max) {
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return $this->max;
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}
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$next = min(! $this->previousWaitTime ? $this->min : $this->previousWaitTime * 2, $this->max);
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$this->previousWaitTime = $next;
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return $next;
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}
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/**
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* Execute and retry the given callback
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*
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* @param callable(?Exception $err): mixed $callback The callback to be retried
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*
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* @return mixed
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* @throws Exception When the given callback throws an exception that can't be retried or max retries is reached
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*/
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public function retry(callable $callback)
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{
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$attempt = 0;
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$previousErr = null;
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do {
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try {
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return $callback($previousErr);
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} catch (Exception $err) {
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if ($attempt >= $this->getRetries() || $err === $previousErr) {
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throw $err;
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}
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$previousErr = $err;
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$sleep = $this->getWaitTime($attempt++);
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usleep($sleep * 1000);
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}
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} while ($attempt <= $this->getRetries());
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}
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}

‎tests/ExponentialBackoffTest.php‎

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<?php
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namespace ipl\Tests\Stdlib;
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use Exception;
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use ipl\Stdlib\ExponentialBackoff;
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use LogicException;
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class ExponentialBackoffTest extends \PHPUnit\Framework\TestCase
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{
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public function testInvalidMaxWaitTime()
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{
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$this->expectException(LogicException::class);
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$this->expectExceptionMessage('Max must be larger than min');
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new ExponentialBackoff(1, 500, 100);
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}
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public function testMinAndMaxWaitTime()
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{
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$backoff = new ExponentialBackoff();
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$this->assertSame(100, $backoff->getMin());
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$this->assertSame(10 * 1000, $backoff->getMax());
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$backoff
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->setMin(200)
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->setMax(500);
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$this->assertSame(200, $backoff->getMin());
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$this->assertSame(500, $backoff->getMax());
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}
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public function testRetriesSetCorrectly()
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{
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$backoff = new ExponentialBackoff();
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$this->assertSame(1, $backoff->getRetries());
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$this->assertSame(5, $backoff->setRetries(5)->getRetries());
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$this->assertNotSame(10, $backoff->setRetries(5)->getRetries());
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}
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public function testGetWaitTime()
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{
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$backoff = new ExponentialBackoff(100, 1000);
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$this->assertSame($backoff->getMin(), $backoff->getWaitTime(0));
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$this->assertGreaterThan($backoff->getWaitTime(0), $backoff->getWaitTime(1));
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$this->assertGreaterThan($backoff->getWaitTime(1), $backoff->getWaitTime(2));
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$this->assertSame($backoff->getMax(), $backoff->getWaitTime(3));
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}
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public function testExecutionRetries()
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{
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$backoff = new ExponentialBackoff(10);
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$attempt = 0;
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$result = $backoff->retry(function (Exception $err = null) use (&$attempt) {
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if (++$attempt < 5) {
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throw new Exception('SQLSTATE[HY000] [2002] No such file or directory');
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}
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return 'succeeded';
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});
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$this->assertSame(5, $attempt);
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$this->assertSame('succeeded', $result);
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}
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public function testExecutionRetriesGivesUpAfterMaxRetries()
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{
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$this->expectException(Exception::class);
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$this->expectExceptionMessage('SQLSTATE[HY000] [2002] No such file or directory');
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$backoff = new ExponentialBackoff(3);
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$backoff->retry(function (Exception $err = null) {
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throw new Exception('SQLSTATE[HY000] [2002] No such file or directory');
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});
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}
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}

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