UnhandledRejectionTracer.php

<?php

use React\Promise\PromiseInterface;

class UnhandledRejectionTracer
{
    private $promises;
    private $unhandledPromiseCallback;

    public function __construct($unhandledPromiseCallback)
    {
        $this->promises = [];
        $this->unhandledPromiseCallback = $unhandledPromiseCallback;
    }

    /**
     * Called when a promise is instanciated
     */
    public function instanciated(PromiseInterface $promise, $reason = null)
    {
        $hash = spl_object_hash($promise);

        // Providing the trace as a string, not as an Exception instance,
        // because this could trigger PHP GC issues; e.g. making a variable
        // rechable again during a __destructor call.
        $exception = new \Exception();
        $trace = "Promise started here: \n" . $exception->getTraceAsString();

        $this->promises[$hash] = [
            'trace' => $trace,
            'reason' => $reason ? $this->stringifyReason($reason) : null,
        ];
    }

    /**
     * Called when a promise has been handled
     */
    public function handled(PromiseInterface $promise)
    {
        $hash = spl_object_hash($promise);

        if (!isset($this->promises[$hash])) {
            return;
        }

        unset($this->promises[$hash]);
    }

    /**
     * Called when a promise is destroyed
     */
    public function destroyed(PromiseInterface $promise)
    {
        $hash = spl_object_hash($promise);

        $this->notifyUnhandledPromise($this->promises[$hash]);

        unset($this->promises[$hash]);
    }

    /**
     * When called at the end of a program, this method returns an array of
     * promises than haven't been handled. They may not have been destroyed
     * because they are still reachable, or because PHP didn't called their
     * destructor.
     */
    public function getRemainingPromises()
    {
        return $this->promises;
    }

    private function notifyUnhandledPromise(array $promiseInfo)
    {
        if (null !== $cb = $this->unhandledPromiseCallback) {
            call_user_func($cb, $promiseInfo);
        }
    }

    private function stringifyReason($reason)
    {
        if (is_object($reason) && method_exists($reason, '__toString')) {
            return (string) $reason;
        }

        return json_encode($reason);
    }
}