react/promise-timer

A trivial implementation of timeouts for Promises, built on top of React PHP.

Usage

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

The below examples assume you use an import statement similar to this:

use React\Promise\Timer;

Timer\timeout(…);

Alternatively, you can also refer to them with their fully-qualified name:

\React\Promise\Timer\timeout(…);

timeout()

The timeout(PromiseInterface $promise, $time, LoopInterface $loop) function can be used to cancel operations that take too long. You need to pass in an input $promise that represents a pending operation and timeout parameters. It returns a new Promise with the following resolution behavior:

• If the input $promise resolves before $time seconds, resolve the resulting promise with its fulfillment value.
• If the input $promise rejects before $time seconds, reject the resulting promise with its rejection value.
• If the input $promise does not settle before $time seconds, cancel the operation and reject the resulting promise with a TimeoutException.

A common use case for handling only resolved values looks like this:

$promise = accessSomeRemoteResource();
Timer\timeout($promise, 10.0, $loop)->then(function ($value) {
    // the operation finished within 10.0 seconds
});

A more complete example could look like this:

$promise = accessSomeRemoteResource();
Timer\timeout($promise, 10.0, $loop)->then(
    function ($value) {
        // the operation finished within 10.0 seconds
    },
    function ($error) {
        if ($error instanceof Timer\TimeoutException) {
            // the operation has failed due to a timeout
        } else {
            // the input operation has failed due to some other error
        }
    }
);

Or if you're using react/promise v2.2.0 or up:

Timer\timeout($promise, 10.0, $loop)
    ->then(function ($value) {
        // the operation finished within 10.0 seconds
    })
    ->otherwise(function (Timer\TimeoutException $error) {
        // the operation has failed due to a timeout
    })
    ->otherwise(function ($error) {
        // the input operation has failed due to some other error
    })
;

Timeout cancellation

As discussed above, the timeout() function will cancel the underlying operation if it takes too long. This means that you can be sure the resulting promise will then be rejected with a TimeoutException.

However, what happens to the underlying input $promise is a bit more tricky: Once the timer fires, we will try to call $promise->cancel() on the input $promise which in turn invokes its cancellation handler.

This means that it's actually up the input $promise to handle cancellation support.

• A common use case involves cleaning up any resources like open network sockets or file handles or terminating external processes or timers.

• If the given input $promise does not support cancellation, then this is a NO-OP. This means that while the resulting promise will still be rejected, the underlying input $promise may still be pending and can hence continue consuming resources.

See the following chapter for more details on the cancellation handler.

Cancellation handler

For example, an implementation for the above operation could look like this:

function accessSomeRemoteResource()
{
    return new Promise(
        function ($resolve, $reject) use (&$socket) {
            // this will be called once the promise is created
            // a common use case involves opening any resources and eventually resolving
            $socket = createSocket();
            $socket->on('data', function ($data) use ($resolve) {
                $resolve($data);
            });
        },
        function ($resolve, $reject) use (&$socket) {
            // this will be called once calling `cancel()` on this promise
            // a common use case involves cleaning any resources and then rejecting
            $socket->close();
            $reject(new \RuntimeException('Operation cancelled'));
        }
    );
}

In this example, calling $promise->cancel() will invoke the registered cancellation handler which then closes the network socket and rejects the Promise instance.

If no cancellation handler is passed to the Promise constructor, then invoking its cancel() method it is effectively a NO-OP. This means that it may still be pending and can hence continue consuming resources.

Note: If you're stuck on legacy versions (PHP 5.3), then this is also a NO-OP, as the Promise cancellation API is currently only available in react/promise v2.1.0 which in turn requires PHP 5.4 or up. It is assumed that if you're actually still stuck on PHP 5.3, resource cleanup is likely one of your smaller problems.

For more details on the promise cancellation, please refer to the Promise documentation.

Collections

If you want to wait for multiple promises to resolve, you can use the normal promise primitives like this:

$promises = array(
    accessSomeRemoteResource(),
    accessSomeRemoteResource(),
    accessSomeRemoteResource()
);

$promise = \React\Promise\all($promises);

Timer\timeout($promise, 10, $loop)->then(function ($values) {
    // *all* promises resolved
});

The applies to all promise collection primitives alike, i.e. all(), race(), any(), some() etc.

For more details on the promise primitives, please refer to the Promise documentation.

resolve()

The resolve($time, LoopInterface $loop) function can be used to create a new Promise that resolves in $time seconds with the $time as the fulfillment value.

Timer\resolve(1.5, $loop)->then(function ($time) {
    echo 'Thanks for waiting ' . $time . ' seconds' . PHP_EOL;
});

reject()

The reject($time, LoopInterface $loop) function can be used to create a new Promise which rejects in $time seconds with a TimeoutException.

Timer\reject(2.0, $loop)->then(null, function (TimeoutException $e) {
    echo '
});

This function complements the resolve() function and can be used as a basic building block for higher-level promise consumers.

TimeoutException

The TimeoutException extends PHP's built-in RuntimeException.

The getTimeout() method can be used to get the timeout value in seconds.

Install

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

{
    "require": {
        "react/promise-timer": "~1.0"
    }
}

Note: If you're stuck on legacy versions (PHP 5.3), then the cancel() method is not available, as the Promise cancellation API is currently only available in react/promise v2.1.0 which in turn requires PHP 5.4 or up.

License

MIT