Async Utilities

Async utilities and fibers for ReactPHP.

This library allows you to manage async control flow. It provides a number of combinators for Promise-based APIs. Instead of nesting or chaining promise callbacks, you can declare them as a list, which is resolved sequentially in an async manner. React/Async will not automagically change blocking code to be async. You need to have an actual event loop and non-blocking libraries interacting with that event loop for it to work. As long as you have a Promise-based API that runs in an event loop, it can be used with this library.

Table of Contents

• Usage
  • async()
  • await()
  • coroutine()
  • delay()
  • parallel()
  • series()
  • waterfall()
• Todo
• Install
• Tests
• License

Usage

This lightweight library consists only of a few simple functions. All functions reside under the React\Async namespace.

The below examples refer to all functions with their fully-qualified names like this:

React\Async\await(…);

As of PHP 5.6+ you can also import each required function into your code like this:

use function React\Async\await;

await(…);

Alternatively, you can also use an import statement similar to this:

use React\Async;

Async\await(…);

async()

The async(callable():(PromiseInterface<T>|T) $function): (callable():PromiseInterface<T>) function can be used to return an async function for a function that uses await() internally.

This function is specifically designed to complement the await() function. The await() function can be considered blocking from the perspective of the calling code. You can avoid this blocking behavior by wrapping it in an async() function call. Everything inside this function will still be blocked, but everything outside this function can be executed asynchronously without blocking:

Loop::addTimer(0.5, React\Async\async(function () {
    echo 'a';
    React\Async\await(React\Promise\Timer\sleep(1.0));
    echo 'c';
}));

Loop::addTimer(1.0, function () {
    echo 'b';
});

// prints "a" at t=0.5s
// prints "b" at t=1.0s
// prints "c" at t=1.5s

See also the await() function for more details.

Note that this function only works in tandem with the await() function. In particular, this function does not "magically" make any blocking function non-blocking:

Loop::addTimer(0.5, React\Async\async(function () {
    echo 'a';
    sleep(1); // broken: using PHP's blocking sleep() for demonstration purposes
    echo 'c';
}));

Loop::addTimer(1.0, function () {
    echo 'b';
});

// prints "a" at t=0.5s
// prints "c" at t=1.5s: Correct timing, but wrong order
// prints "b" at t=1.5s: Triggered too late because it was blocked

As an alternative, you should always make sure to use this function in tandem with the await() function and an async API returning a promise as shown in the previous example.

The async() function is specifically designed for cases where it is used as a callback (such as an event loop timer, event listener, or promise callback). For this reason, it returns a new function wrapping the given $function instead of directly invoking it and returning its value.

use function React\Async\async;

Loop::addTimer(1.0, async(function () { … }));
$connection->on('close', async(function () { … }));
$stream->on('data', async(function ($data) { … }));
$promise->then(async(function (int $result) { … }));

You can invoke this wrapping function to invoke the given $function with any arguments given as-is. The function will always return a Promise which will be fulfilled with whatever your $function returns. Likewise, it will return a promise that will be rejected if you throw an Exception or Throwable from your $function. This allows you to easily create Promise-based functions:

$promise = React\Async\async(function (): int {
    $browser = new React\Http\Browser();
    $urls = [
        'https://example.com/alice',
        'https://example.com/bob'
    ];

    $bytes = 0;
    foreach ($urls as $url) {
        $response = React\Async\await($browser->get($url));
        assert($response instanceof Psr\Http\Message\ResponseInterface);
        $bytes += $response->getBody()->getSize();
    }
    return $bytes;
})();

$promise->then(function (int $bytes) {
    echo 'Total size: ' . $bytes . PHP_EOL;
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

The previous example uses await() inside a loop to highlight how this vastly simplifies consuming asynchronous operations. At the same time, this naive example does not leverage concurrent execution, as it will essentially "await" between each operation. In order to take advantage of concurrent execution within the given $function, you can "await" multiple promises by using a single await() together with Promise-based primitives like this:

$promise = React\Async\async(function (): int {
    $browser = new React\Http\Browser();
    $urls = [
        'https://example.com/alice',
        'https://example.com/bob'
    ];

    $promises = [];
    foreach ($urls as $url) {
        $promises[] = $browser->get($url);
    }

    try {
        $responses = React\Async\await(React\Promise\all($promises));
    } catch (Exception $e) {
        foreach ($promises as $promise) {
            $promise->cancel();
        }
        throw $e;
    }

    $bytes = 0;
    foreach ($responses as $response) {
        assert($response instanceof Psr\Http\Message\ResponseInterface);
        $bytes += $response->getBody()->getSize();
    }
    return $bytes;
})();

$promise->then(function (int $bytes) {
    echo 'Total size: ' . $bytes . PHP_EOL;
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

The returned promise is implemented in such a way that it can be cancelled when it is still pending. Cancelling a pending promise will cancel any awaited promises inside that fiber or any nested fibers. As such, the following example will only output ab and cancel the pending delay(). The await() calls in this example would throw a RuntimeException from the cancelled delay() call that bubbles up through the fibers.

$promise = async(static function (): int {
    echo 'a';
    await(async(static function (): void {
        echo 'b';
        delay(2);
        echo 'c';
    })());
    echo 'd';

    return time();
})();

$promise->cancel();
await($promise);

await()

The await(PromiseInterface<T> $promise): T function can be used to block waiting for the given $promise to be fulfilled.

$result = React\Async\await($promise);

This function will only return after the given $promise has settled, i.e. either fulfilled or rejected. While the promise is pending, this function can be considered blocking from the perspective of the calling code. You can avoid this blocking behavior by wrapping it in an async() function call. Everything inside this function will still be blocked, but everything outside this function can be executed asynchronously without blocking:

Loop::addTimer(0.5, React\Async\async(function () {
    echo 'a';
    React\Async\await(React\Promise\Timer\sleep(1.0));
    echo 'c';
}));

Loop::addTimer(1.0, function () {
    echo 'b';
});

// prints "a" at t=0.5s
// prints "b" at t=1.0s
// prints "c" at t=1.5s

See also the async() function for more details.

Once the promise is fulfilled, this function will return whatever the promise resolved to.

Once the promise is rejected, this will throw whatever the promise rejected with. If the promise did not reject with an Exception or Throwable, then this function will throw an UnexpectedValueException instead.

try {
    $result = React\Async\await($promise);
    // promise successfully fulfilled with $result
    echo 'Result: ' . $result;
} catch (Throwable $e) {
    // promise rejected with $e
    echo 'Error: ' . $e->getMessage();
}

coroutine()

The coroutine(callable(mixed ...$args):(\Generator|PromiseInterface<T>|T) $function, mixed ...$args): PromiseInterface<T> function can be used to execute a Generator-based coroutine to "await" promises.

React\Async\coroutine(function () {
    $browser = new React\Http\Browser();

    try {
        $response = yield $browser->get('https://example.com/');
        assert($response instanceof Psr\Http\Message\ResponseInterface);
        echo $response->getBody();
    } catch (Exception $e) {
        echo 'Error: ' . $e->getMessage() . PHP_EOL;
    }
});

Using Generator-based coroutines is an alternative to directly using the underlying promise APIs. For many use cases, this makes using promise-based APIs much simpler, as it resembles a synchronous code flow more closely. The above example performs the equivalent of directly using the promise APIs:

$browser = new React\Http\Browser();

$browser->get('https://example.com/')->then(function (Psr\Http\Message\ResponseInterface $response) {
    echo $response->getBody();
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

The yield keyword can be used to "await" a promise resolution. Internally, it will turn the entire given $function into a Generator. This allows the execution to be interrupted and resumed at the same place when the promise is fulfilled. The yield statement returns whatever the promise is fulfilled with. If the promise is rejected, it will throw an Exception or Throwable.

The coroutine() function will always return a Promise which will be fulfilled with whatever your $function returns. Likewise, it will return a promise that will be rejected if you throw an Exception or Throwable from your $function. This allows you to easily create Promise-based functions:

$promise = React\Async\coroutine(function () {
    $browser = new React\Http\Browser();
    $urls = [
        'https://example.com/alice',
        'https://example.com/bob'
    ];

    $bytes = 0;
    foreach ($urls as $url) {
        $response = yield $browser->get($url);
        assert($response instanceof Psr\Http\Message\ResponseInterface);
        $bytes += $response->getBody()->getSize();
    }
    return $bytes;
});

$promise->then(function (int $bytes) {
    echo 'Total size: ' . $bytes . PHP_EOL;
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

The previous example uses a yield statement inside a loop to highlight how this vastly simplifies consuming asynchronous operations. At the same time, this naive example does not leverage concurrent execution, as it will essentially "await" between each operation. In order to take advantage of concurrent execution within the given $function, you can "await" multiple promises by using a single yield together with Promise-based primitives like this:

$promise = React\Async\coroutine(function () {
    $browser = new React\Http\Browser();
    $urls = [
        'https://example.com/alice',
        'https://example.com/bob'
    ];

    $promises = [];
    foreach ($urls as $url) {
        $promises[] = $browser->get($url);
    }

    try {
        $responses = yield React\Promise\all($promises);
    } catch (Exception $e) {
        foreach ($promises as $promise) {
            $promise->cancel();
        }
        throw $e;
    }

    $bytes = 0;
    foreach ($responses as $response) {
        assert($response instanceof Psr\Http\Message\ResponseInterface);
        $bytes += $response->getBody()->getSize();
    }
    return $bytes;
});

$promise->then(function (int $bytes) {
    echo 'Total size: ' . $bytes . PHP_EOL;
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

delay()

The delay(float $seconds): void function can be used to delay program execution for duration given in $seconds.

React\Async\delay($seconds);

This function will only return after the given number of $seconds have elapsed. If there are no other events attached to this loop, it will behave similar to PHP's sleep() function.

echo 'a';
React\Async\delay(1.0);
echo 'b';

// prints "a" at t=0.0s
// prints "b" at t=1.0s

Unlike PHP's sleep() function, this function may not necessarily halt execution of the entire process thread. Instead, it allows the event loop to run any other events attached to the same loop until the delay returns:

echo 'a';
Loop::addTimer(1.0, function (): void {
    echo 'b';
});
React\Async\delay(3.0);
echo 'c';

// prints "a" at t=0.0s
// prints "b" at t=1.0s
// prints "c" at t=3.0s

This behavior is especially useful if you want to delay the program execution of a particular routine, such as when building a simple polling or retry mechanism:

try {
    something();
} catch (Throwable) {
    // in case of error, retry after a short delay
    React\Async\delay(1.0);
    something();
}

Because this function only returns after some time has passed, it can be considered blocking from the perspective of the calling code. You can avoid this blocking behavior by wrapping it in an async() function call. Everything inside this function will still be blocked, but everything outside this function can be executed asynchronously without blocking:

Loop::addTimer(0.5, React\Async\async(function (): void {
    echo 'a';
    React\Async\delay(1.0);
    echo 'c';
}));

Loop::addTimer(1.0, function (): void {
    echo 'b';
});

// prints "a" at t=0.5s
// prints "b" at t=1.0s
// prints "c" at t=1.5s

See also the async() function for more details.

Internally, the $seconds argument will be used as a timer for the loop so that it keeps running until this timer triggers. This implies that if you pass a really small (or negative) value, it will still start a timer and will thus trigger at the earliest possible time in the future.

The function is implemented in such a way that it can be cancelled when it is running inside an async() function. Cancelling the resulting promise will clean up any pending timers and throw a RuntimeException from the pending delay which in turn would reject the resulting promise.

$promise = async(function (): void {
    echo 'a';
    delay(3.0);
    echo 'b';
})();

Loop::addTimer(2.0, function () use ($promise): void {
    $promise->cancel();
});

// prints "a" at t=0.0s
// rejects $promise at t=2.0
// never prints "b"

parallel()

The parallel(iterable<callable():PromiseInterface<T>> $tasks): PromiseInterface<array<T>> function can be used like this:

<?php

use React\EventLoop\Loop;
use React\Promise\Promise;

React\Async\parallel([
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for a whole second');
            });
        });
    },
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for another whole second');
            });
        });
    },
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for yet another whole second');
            });
        });
    },
])->then(function (array $results) {
    foreach ($results as $result) {
        var_dump($result);
    }
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

series()

The series(iterable<callable():PromiseInterface<T>> $tasks): PromiseInterface<array<T>> function can be used like this:

<?php

use React\EventLoop\Loop;
use React\Promise\Promise;

React\Async\series([
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for a whole second');
            });
        });
    },
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for another whole second');
            });
        });
    },
    function () {
        return new Promise(function ($resolve) {
            Loop::addTimer(1, function () use ($resolve) {
                $resolve('Slept for yet another whole second');
            });
        });
    },
])->then(function (array $results) {
    foreach ($results as $result) {
        var_dump($result);
    }
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

waterfall()

The waterfall(iterable<callable(mixed=):PromiseInterface<T>> $tasks): PromiseInterface<T> function can be used like this:

<?php

use React\EventLoop\Loop;
use React\Promise\Promise;

$addOne = function ($prev = 0) {
    return new Promise(function ($resolve) use ($prev) {
        Loop::addTimer(1, function () use ($prev, $resolve) {
            $resolve($prev + 1);
        });
    });
};

React\Async\waterfall([
    $addOne,
    $addOne,
    $addOne
])->then(function ($prev) {
    echo "Final result is $prev\n";
}, function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;
});

Todo

• Implement queue()

Install

The recommended way to install this library is through Composer. New to Composer?

This project follows SemVer. This will install the latest supported version from this branch:

composer require react/async:^4.3

See also the CHANGELOG for details about version upgrades.

This project aims to run on any platform and thus does not require any PHP extensions and supports running on PHP 8.1+. It's highly recommended to use the latest supported PHP version for this project.

We're committed to providing long-term support (LTS) options and to provide a smooth upgrade path. If you're using an older PHP version, you may use the 3.x branch (PHP 7.1+) or 2.x branch (PHP 5.3+) which both provide a compatible API but do not take advantage of newer language features. You may target multiple versions at the same time to support a wider range of PHP versions like this:

composer require "react/async:^4 || ^3 || ^2"

Tests

To run the test suite, you first need to clone this repo and then install all dependencies through Composer:

composer install

To run the test suite, go to the project root and run:

vendor/bin/phpunit

On top of this, we use PHPStan on max level to ensure type safety across the project:

vendor/bin/phpstan

License

MIT, see LICENSE file.

This project is heavily influenced by async.js.