281 lines
8.6 KiB
PHP
281 lines
8.6 KiB
PHP
<?php
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namespace GuzzleHttp\Promise;
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/**
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* Promises/A+ implementation that avoids recursion when possible.
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*
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* @link https://promisesaplus.com/
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*/
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class Promise implements PromiseInterface
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{
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private $state = self::PENDING;
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private $result;
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private $cancelFn;
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private $waitFn;
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private $waitList;
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private $handlers = [];
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/**
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* @param callable $waitFn Fn that when invoked resolves the promise.
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* @param callable $cancelFn Fn that when invoked cancels the promise.
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*/
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public function __construct(
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callable $waitFn = null,
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callable $cancelFn = null
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) {
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$this->waitFn = $waitFn;
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$this->cancelFn = $cancelFn;
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}
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public function then(
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callable $onFulfilled = null,
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callable $onRejected = null
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) {
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if ($this->state === self::PENDING) {
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$p = new Promise(null, [$this, 'cancel']);
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$this->handlers[] = [$p, $onFulfilled, $onRejected];
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$p->waitList = $this->waitList;
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$p->waitList[] = $this;
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return $p;
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}
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// Return a fulfilled promise and immediately invoke any callbacks.
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if ($this->state === self::FULFILLED) {
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return $onFulfilled
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? promise_for($this->result)->then($onFulfilled)
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: promise_for($this->result);
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}
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// It's either cancelled or rejected, so return a rejected promise
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// and immediately invoke any callbacks.
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$rejection = rejection_for($this->result);
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return $onRejected ? $rejection->then(null, $onRejected) : $rejection;
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}
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public function otherwise(callable $onRejected)
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{
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return $this->then(null, $onRejected);
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}
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public function wait($unwrap = true)
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{
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$this->waitIfPending();
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$inner = $this->result instanceof PromiseInterface
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? $this->result->wait($unwrap)
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: $this->result;
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if ($unwrap) {
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if ($this->result instanceof PromiseInterface
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|| $this->state === self::FULFILLED
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) {
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return $inner;
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} else {
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// It's rejected so "unwrap" and throw an exception.
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throw exception_for($inner);
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}
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}
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}
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public function getState()
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{
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return $this->state;
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}
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public function cancel()
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{
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if ($this->state !== self::PENDING) {
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return;
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}
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$this->waitFn = $this->waitList = null;
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if ($this->cancelFn) {
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$fn = $this->cancelFn;
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$this->cancelFn = null;
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try {
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$fn();
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} catch (\Throwable $e) {
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$this->reject($e);
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} catch (\Exception $e) {
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$this->reject($e);
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}
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}
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// Reject the promise only if it wasn't rejected in a then callback.
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if ($this->state === self::PENDING) {
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$this->reject(new CancellationException('Promise has been cancelled'));
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}
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}
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public function resolve($value)
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{
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$this->settle(self::FULFILLED, $value);
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}
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public function reject($reason)
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{
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$this->settle(self::REJECTED, $reason);
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}
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private function settle($state, $value)
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{
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if ($this->state !== self::PENDING) {
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// Ignore calls with the same resolution.
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if ($state === $this->state && $value === $this->result) {
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return;
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}
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throw $this->state === $state
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? new \LogicException("The promise is already {$state}.")
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: new \LogicException("Cannot change a {$this->state} promise to {$state}");
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}
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if ($value === $this) {
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throw new \LogicException('Cannot fulfill or reject a promise with itself');
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}
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// Clear out the state of the promise but stash the handlers.
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$this->state = $state;
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$this->result = $value;
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$handlers = $this->handlers;
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$this->handlers = null;
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$this->waitList = $this->waitFn = null;
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$this->cancelFn = null;
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if (!$handlers) {
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return;
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}
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// If the value was not a settled promise or a thenable, then resolve
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// it in the task queue using the correct ID.
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if (!method_exists($value, 'then')) {
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$id = $state === self::FULFILLED ? 1 : 2;
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// It's a success, so resolve the handlers in the queue.
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queue()->add(static function () use ($id, $value, $handlers) {
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foreach ($handlers as $handler) {
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self::callHandler($id, $value, $handler);
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}
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});
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} elseif ($value instanceof Promise
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&& $value->getState() === self::PENDING
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) {
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// We can just merge our handlers onto the next promise.
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$value->handlers = array_merge($value->handlers, $handlers);
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} else {
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// Resolve the handlers when the forwarded promise is resolved.
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$value->then(
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static function ($value) use ($handlers) {
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foreach ($handlers as $handler) {
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self::callHandler(1, $value, $handler);
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}
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},
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static function ($reason) use ($handlers) {
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foreach ($handlers as $handler) {
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self::callHandler(2, $reason, $handler);
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}
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}
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);
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}
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}
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/**
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* Call a stack of handlers using a specific callback index and value.
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*
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* @param int $index 1 (resolve) or 2 (reject).
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* @param mixed $value Value to pass to the callback.
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* @param array $handler Array of handler data (promise and callbacks).
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*
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* @return array Returns the next group to resolve.
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*/
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private static function callHandler($index, $value, array $handler)
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{
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/** @var PromiseInterface $promise */
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$promise = $handler[0];
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// The promise may have been cancelled or resolved before placing
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// this thunk in the queue.
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if ($promise->getState() !== self::PENDING) {
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return;
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}
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try {
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if (isset($handler[$index])) {
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$promise->resolve($handler[$index]($value));
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} elseif ($index === 1) {
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// Forward resolution values as-is.
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$promise->resolve($value);
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} else {
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// Forward rejections down the chain.
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$promise->reject($value);
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}
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} catch (\Throwable $reason) {
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$promise->reject($reason);
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} catch (\Exception $reason) {
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$promise->reject($reason);
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}
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}
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private function waitIfPending()
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{
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if ($this->state !== self::PENDING) {
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return;
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} elseif ($this->waitFn) {
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$this->invokeWaitFn();
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} elseif ($this->waitList) {
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$this->invokeWaitList();
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} else {
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// If there's not wait function, then reject the promise.
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$this->reject('Cannot wait on a promise that has '
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. 'no internal wait function. You must provide a wait '
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. 'function when constructing the promise to be able to '
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. 'wait on a promise.');
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}
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queue()->run();
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if ($this->state === self::PENDING) {
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$this->reject('Invoking the wait callback did not resolve the promise');
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}
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}
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private function invokeWaitFn()
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{
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try {
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$wfn = $this->waitFn;
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$this->waitFn = null;
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$wfn(true);
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} catch (\Exception $reason) {
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if ($this->state === self::PENDING) {
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// The promise has not been resolved yet, so reject the promise
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// with the exception.
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$this->reject($reason);
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} else {
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// The promise was already resolved, so there's a problem in
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// the application.
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throw $reason;
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}
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}
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}
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private function invokeWaitList()
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{
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$waitList = $this->waitList;
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$this->waitList = null;
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foreach ($waitList as $result) {
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while (true) {
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$result->waitIfPending();
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if ($result->result instanceof Promise) {
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$result = $result->result;
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} else {
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if ($result->result instanceof PromiseInterface) {
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$result->result->wait(false);
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}
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break;
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}
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}
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}
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}
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}
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