Endeavor (PHP)

Endeavor is a PHP utility to retry anything, using various strategies.

Requirements

• PHP 7.4+

Installation

Using Composer:

composer require prismamedia/php-endeavor

Usage

Simply wrap the code you want to retry in a Closure in the run() method:

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\ConstantStrategy;

$endeavor = new Endeavor(new ConstantStrategy(500));
$endeavor->run(function () {
    // Code which can throw any \Throwable
});

By default, Endeavor will try to run the given code 5 times. If the first attempt is successful, Endeavor will stop. But if the code fails at each attempt, Endeavor will throw an exception on the last attempt.

The maximum number of attempts can be specified using the second argument of the constructor:

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\ConstantStrategy;

$endeavor = new Endeavor(new ConstantStrategy(500), 3);
$endeavor->run(function () {
    // Code which can throw any \Throwable
});

In this example, it will run the code 3 times and throw on the third attempt if it continues to fail.

Keep in mind that the maximum number of attempts includes the first.

A maximum delay can be specified to create a ceiling using the third argument of the constructor:

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\ExponentialStrategy;

$endeavor = new Endeavor(new ExponentialStrategy(1000), 5, 5000);
$endeavor->run(function () {
    // Code which can throw any \Throwable
});

In this example, the code will be executed 5 times with an exponential strategy which doubles the delay at each attempt to a maximum of 5 seconds.

Strategies

Endeavor can be instantiated with various strategies, depending on the expected retry interval.

Each strategy takes a required delay in milliseconds and compute the next attempt delay based on the nature of the strategy.

ConstantStrategy

This is the simplest strategy. It takes a fixed delay and sets the interval between attempt to that number.

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\ConstantStrategy;

$endeavor = new Endeavor(new ConstantStrategy(100));
$endeavor->run(function () {
    throw new \RuntimeException('Failing');
});

// 1st attempt: immediate
// 2nd attempt: 100ms
// 3rd attempt: 100ms
// 4th attempt: 100ms
// 5th attempt: 100ms

LinearStrategy

This strategy takes an initial delay and adds it up at each attempt.

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\LinearStrategy;

$endeavor = new Endeavor(new LinearStrategy(100));
$endeavor->run(function () {
    throw new \RuntimeException('Failing');
});

// 1st attempt: immediate
// 2nd attempt: 100ms
// 3rd attempt: 200ms
// 4th attempt: 300ms
// 5th attempt: 400ms

ExponentialStrategy

This strategy takes an initial delay and doubles it at each attempt.

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\ExponentialStrategy;

$endeavor = new Endeavor(new ExponentialStrategy(100));
$endeavor->run(function () {
    throw new \RuntimeException('Failing');
});

// 1st attempt: immediate
// 2nd attempt: 100ms
// 3rd attempt: 200ms
// 4th attempt: 400ms
// 5th attempt: 800ms

MultiplicativeStrategy

This strategy takes an initial delay and a multiplier then multiplies the delay at each attempt.

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\MultiplicativeStrategy;

$endeavor = new Endeavor(new MultiplicativeStrategy(100, 3));
$endeavor->run(function () {
    throw new \RuntimeException('Failing');
});

// 1st attempt: immediate
// 2nd attempt: 100ms
// 3rd attempt: 300ms
// 4th attempt: 900ms
// 5th attempt: 2700ms

Error handling

By default, Endeavor will simply retry the code when an Exception is thrown, then throw the last encountered Exception when reaching the maximum number of attempts.

An error handler can be specified using a Closure which will be executed after each unsuccessful attempt.

It can be used for logging purpose:

use PrismaMedia\Endeavor\Endeavor;
use PrismaMedia\Endeavor\Strategy\LinearStrategy;

$endeavor = new Endeavor(new LinearStrategy(500));
$endeavor->setErrorHandler(function (Endeavor $endeavor, \Throwable $e, int $attempt) {
    // $endeavor is the current instance
    // $e is the thrown Exception during this attempt
    // $attempt is the current attempt number
    $this->logger->error(
        'Something went wrong on the attempt #{attempt}: {error}',
        [
            'attempt' => $attempt,
            'error' => $e->getMessage(),
        ]
    );
});
$endeavor->run(function () {
    throw new \RuntimeException('Failing');
});

Or even throwing another Exception and stopping Endeavor if the error is unrecoverable:

$endeavor->setErrorHandler(function (Endeavor $endeavor, \Throwable $e, int $attempt) {
    if ($e instanceof OneSpecificException) {
        throw $e
    }
});

It can also be used to change the current strategy:

$endeavor->setErrorHandler(function (Endeavor $endeavor, \Throwable $e, int $attempt) {
    if ($e instanceof UnreachableDatabaseException) {
        $endeavor->setStrategy(new ConstantStrategy(5000));
    }
});

Testing

Testing a class which uses Endeavor can dramatically slow down the execution of tests.

Symfony context

On a Symfony project, this can be resolved using the symfony/phpunit-bridge package and the included ClockMock.

See the documentation on how to setup the bridge and use the @group time-sensitive annotation.

Finally, on the tests/bootstrap.php (documentation), register the Endeavor class:

# tests/boostrap.php
<?php

use PrismaMedia\Endeavor\Endeavor;
use Symfony\Bridge\PhpUnit\ClockMock;
use Symfony\Component\Dotenv\Dotenv;

require dirname(__DIR__).'/vendor/autoload.php';

if (file_exists(dirname(__DIR__).'/config/bootstrap.php')) {
    require dirname(__DIR__).'/config/bootstrap.php';
} elseif (method_exists(Dotenv::class, 'bootEnv')) {
    (new Dotenv())->bootEnv(dirname(__DIR__).'/.env');
}

// Register Endeavor in ClockMock to skip the waiting time between retries
ClockMock::register(Endeavor::class);

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License

BSD 3-Clause