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amp/lib/Internal/Placeholder.php

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<?php
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namespace Amp\Internal;
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use Amp\Coroutine;
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use Amp\Failure;
use Amp\Loop;
use Amp\Promise;
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use React\Promise\PromiseInterface as ReactPromise;
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/**
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* Trait used by Promise implementations. Do not use this trait in your code, instead compose your class from one of
* the available classes implementing \Amp\Promise.
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*
* @internal
*/
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trait Placeholder {
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/** @var bool */
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private $resolved = false;
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/** @var mixed */
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private $result;
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/** @var callable|\Amp\Internal\ResolutionQueue|null */
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private $onResolved;
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/** @var null|array */
private $resolutionTrace;
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/**
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* @inheritdoc
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*/
public function onResolve(callable $onResolved) {
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if ($this->resolved) {
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if ($this->result instanceof Promise) {
$this->result->onResolve($onResolved);
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return;
}
try {
$result = $onResolved(null, $this->result);
if ($result === null) {
return;
}
if ($result instanceof \Generator) {
$result = new Coroutine($result);
}
if ($result instanceof Promise || $result instanceof ReactPromise) {
Promise\rethrow($result);
}
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} catch (\Throwable $exception) {
Loop::defer(function () use ($exception) {
throw $exception;
});
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}
return;
}
if (null === $this->onResolved) {
$this->onResolved = $onResolved;
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return;
}
if (!$this->onResolved instanceof ResolutionQueue) {
$this->onResolved = new ResolutionQueue($this->onResolved);
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}
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$this->onResolved->push($onResolved);
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}
/**
* @param mixed $value
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*
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* @throws \Error Thrown if the promise has already been resolved.
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*/
private function resolve($value = null) {
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if ($this->resolved) {
$message = "Promise has already been resolved";
if (isset($this->resolutionTrace)) {
$trace = formatStacktrace($this->resolutionTrace);
$message .= ". Previous resolution trace:\n\n{$trace}\n\n";
} else {
$message .= ", define const AMP_DEBUG_PLACEHOLDER_DOUBLE_RESOLUTION = true and enable assertions for a stacktrace of the previous resolution.";
}
throw new \Error($message);
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}
assert((function () {
if (\defined("AMP_DEBUG_PLACEHOLDER_DOUBLE_RESOLUTION") && AMP_DEBUG_PLACEHOLDER_DOUBLE_RESOLUTION) {
$trace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
array_shift($trace); // remove current closure
$this->resolutionTrace = $trace;
}
return true;
})());
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if ($value instanceof ReactPromise) {
$value = Promise\adapt($value);
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}
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$this->resolved = true;
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$this->result = $value;
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if ($this->onResolved === null) {
return;
}
$onResolved = $this->onResolved;
$this->onResolved = null;
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if ($this->result instanceof Promise) {
$this->result->onResolve($onResolved);
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return;
}
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try {
$result = $onResolved(null, $this->result);
if ($result === null) {
return;
}
if ($result instanceof \Generator) {
$result = new Coroutine($result);
}
if ($result instanceof Promise || $result instanceof ReactPromise) {
Promise\rethrow($result);
}
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} catch (\Throwable $exception) {
Loop::defer(function () use ($exception) {
throw $exception;
});
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}
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}
/**
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* @param \Throwable $reason Failure reason.
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*/
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private function fail(\Throwable $reason) {
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$this->resolve(new Failure($reason));
}
}