mirror of
https://github.com/danog/amp.git
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212 lines
5.6 KiB
PHP
212 lines
5.6 KiB
PHP
<?php
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namespace Amp\Internal;
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use Amp\Deferred;
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use Amp\Failure;
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use Amp\Promise;
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use Amp\Success;
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use React\Promise\PromiseInterface as ReactPromise;
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/**
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* Trait used by Iterator implementations. Do not use this trait in your code, instead compose your class from one of
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* the available classes implementing \Amp\Iterator.
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* Note that it is the responsibility of the user of this trait to ensure that listeners have a chance to listen first
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* before emitting values.
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*
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* @internal
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* @template-covariant TValue
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*/
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trait Producer
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{
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/** @var Promise|null */
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private $complete;
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/** @var mixed[] */
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private $values = [];
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/** @var Deferred[] */
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private $backPressure = [];
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/** @var int */
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private $consumePosition = -1;
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/** @var int */
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private $emitPosition = -1;
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/** @var Deferred|null */
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private $waiting;
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/** @var null|array */
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private $resolutionTrace;
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/**
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* {@inheritdoc}
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*
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* @return Promise<bool>
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*/
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public function advance(): Promise
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{
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if ($this->waiting !== null) {
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throw new \Error("The prior promise returned must resolve before invoking this method again");
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}
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unset($this->values[$this->consumePosition]);
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$position = ++$this->consumePosition;
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if (\array_key_exists($position, $this->values)) {
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\assert(isset($this->backPressure[$position]));
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$deferred = $this->backPressure[$position];
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unset($this->backPressure[$position]);
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$deferred->resolve();
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return new Success(true);
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}
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if ($this->complete) {
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return $this->complete;
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}
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$this->waiting = new Deferred;
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return $this->waiting->promise();
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}
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/**
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* {@inheritdoc}
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*
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* @return TValue
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*/
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public function getCurrent()
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{
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if (empty($this->values) && $this->complete) {
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throw new \Error("The iterator has completed");
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}
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if (!\array_key_exists($this->consumePosition, $this->values)) {
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throw new \Error("Promise returned from advance() must resolve before calling this method");
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}
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return $this->values[$this->consumePosition];
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}
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/**
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* Emits a value from the iterator. The returned promise is resolved once the emitted value has been consumed.
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*
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* @param mixed $value
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*
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* @return Promise
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* @psalm-return Promise<null>
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*
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* @throws \Error If the iterator has completed.
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*/
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private function emit($value): Promise
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{
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if ($this->complete) {
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throw new \Error("Iterators cannot emit values after calling complete");
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}
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if ($value instanceof ReactPromise) {
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$value = Promise\adapt($value);
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}
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if ($value instanceof Promise) {
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$deferred = new Deferred;
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$value->onResolve(function ($e, $v) use ($deferred) {
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if ($this->complete) {
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$deferred->fail(
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new \Error("The iterator was completed before the promise result could be emitted")
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);
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return;
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}
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if ($e) {
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$this->fail($e);
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$deferred->fail($e);
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return;
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}
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$deferred->resolve($this->emit($v));
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});
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return $deferred->promise();
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}
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$position = ++$this->emitPosition;
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$this->values[$position] = $value;
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if ($this->waiting !== null) {
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$waiting = $this->waiting;
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$this->waiting = null;
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$waiting->resolve(true);
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return new Success; // Consumer was already waiting for a new value, so back-pressure is unnecessary.
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}
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$this->backPressure[$position] = $pressure = new Deferred;
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return $pressure->promise();
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}
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/**
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* Completes the iterator.
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*
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* @return void
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*
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* @throws \Error If the iterator has already been completed.
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*/
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private function complete()
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{
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if ($this->complete) {
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$message = "Iterator has already been completed";
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if (isset($this->resolutionTrace)) {
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$trace = formatStacktrace($this->resolutionTrace);
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$message .= ". Previous completion trace:\n\n{$trace}\n\n";
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} else {
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// @codeCoverageIgnoreStart
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$message .= ", define environment variable AMP_DEBUG or const AMP_DEBUG = true and enable assertions "
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. "for a stacktrace of the previous resolution.";
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// @codeCoverageIgnoreEnd
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}
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throw new \Error($message);
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}
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\assert((function () {
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if (isDebugEnabled()) {
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$trace = \debug_backtrace(\DEBUG_BACKTRACE_IGNORE_ARGS);
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\array_shift($trace); // remove current closure
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$this->resolutionTrace = $trace;
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}
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return true;
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})());
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$this->complete = new Success(false);
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if ($this->waiting !== null) {
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$waiting = $this->waiting;
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$this->waiting = null;
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$waiting->resolve($this->complete);
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}
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}
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/**
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* @param \Throwable $exception
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*
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* @return void
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*/
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private function fail(\Throwable $exception)
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{
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$this->complete = new Failure($exception);
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if ($this->waiting !== null) {
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$waiting = $this->waiting;
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$this->waiting = null;
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$waiting->resolve($this->complete);
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}
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}
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}
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