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<?php |
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namespace GraphQL\Executor\Promise\Adapter; |
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use GraphQL\Utils\Utils; |
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/** |
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* Class SyncPromise |
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* |
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* Simplistic (yet full-featured) implementation of Promises A+ spec for regular PHP `sync` mode |
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* (using queue to defer promises execution) |
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* |
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* @package GraphQL\Executor\Promise\Adapter |
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*/ |
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class SyncPromise |
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{ |
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const PENDING = 'pending'; |
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const FULFILLED = 'fulfilled'; |
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const REJECTED = 'rejected'; |
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/** |
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* @var \SplQueue |
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*/ |
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public static $queue; |
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public static function getQueue() |
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{ |
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return self::$queue ?: self::$queue = new \SplQueue(); |
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} |
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public static function runQueue() |
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{ |
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$q = self::$queue; |
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while ($q && !$q->isEmpty()) { |
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$task = $q->dequeue(); |
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$task(); |
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} |
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} |
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public $state = self::PENDING; |
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public $result; |
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/** |
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* Promises created in `then` method of this promise and awaiting for resolution of this promise |
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* @var array |
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*/ |
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private $waiting = []; |
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public function reject($reason) |
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{ |
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if (!$reason instanceof \Exception && !$reason instanceof \Throwable) { |
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throw new \Exception('SyncPromise::reject() has to be called with an instance of \Throwable'); |
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} |
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switch ($this->state) { |
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case self::PENDING: |
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$this->state = self::REJECTED; |
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$this->result = $reason; |
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$this->enqueueWaitingPromises(); |
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break; |
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case self::REJECTED: |
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if ($reason !== $this->result) { |
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throw new \Exception("Cannot change rejection reason"); |
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} |
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break; |
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case self::FULFILLED: |
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throw new \Exception("Cannot reject fulfilled promise"); |
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} |
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return $this; |
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} |
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public function resolve($value) |
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{ |
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switch ($this->state) { |
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case self::PENDING: |
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if ($value === $this) { |
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throw new \Exception("Cannot resolve promise with self"); |
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} |
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if (is_object($value) && method_exists($value, 'then')) { |
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$value->then( |
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function($resolvedValue) { |
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$this->resolve($resolvedValue); |
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}, |
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function($reason) { |
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$this->reject($reason); |
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} |
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); |
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return $this; |
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} |
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$this->state = self::FULFILLED; |
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$this->result = $value; |
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$this->enqueueWaitingPromises(); |
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break; |
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case self::FULFILLED: |
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if ($this->result !== $value) { |
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throw new \Exception("Cannot change value of fulfilled promise"); |
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} |
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break; |
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case self::REJECTED: |
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throw new \Exception("Cannot resolve rejected promise"); |
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} |
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return $this; |
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} |
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public function then(callable $onFulfilled = null, callable $onRejected = null) |
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{ |
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if ($this->state === self::REJECTED && !$onRejected) { |
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return $this; |
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} |
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if ($this->state === self::FULFILLED && !$onFulfilled) { |
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return $this; |
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} |
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$tmp = new self(); |
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$this->waiting[] = [$tmp, $onFulfilled, $onRejected]; |
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if ($this->state !== self::PENDING) { |
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$this->enqueueWaitingPromises(); |
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} |
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return $tmp; |
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} |
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private function enqueueWaitingPromises() |
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{ |
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Utils::invariant($this->state !== self::PENDING, 'Cannot enqueue derived promises when parent is still pending'); |
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foreach ($this->waiting as $descriptor) { |
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self::getQueue()->enqueue(function () use ($descriptor) { |
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/** @var $promise self */ |
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list($promise, $onFulfilled, $onRejected) = $descriptor; |
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if ($this->state === self::FULFILLED) { |
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try { |
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$promise->resolve($onFulfilled ? $onFulfilled($this->result) : $this->result); |
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} catch (\Exception $e) { |
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$promise->reject($e); |
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} catch (\Throwable $e) { |
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$promise->reject($e); |
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} |
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} else if ($this->state === self::REJECTED) { |
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try { |
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if ($onRejected) { |
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$promise->resolve($onRejected($this->result)); |
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} else { |
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$promise->reject($this->result); |
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} |
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} catch (\Exception $e) { |
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$promise->reject($e); |
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} catch (\Throwable $e) { |
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$promise->reject($e); |
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} |
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} |
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}); |
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} |
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$this->waiting = []; |
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} |
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} |
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