PocketMine-MP/src/scheduler/AsyncTask.php

<?php

/*
 *
 *  ____            _        _   __  __ _                  __  __ ____
 * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
 * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
 * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
 * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * @author PocketMine Team
 * @link http://www.pocketmine.net/
 *
 *
 */

declare(strict_types=1);

namespace pocketmine\scheduler;

use pocketmine\utils\AssumptionFailedError;
use function igbinary_serialize;
use function igbinary_unserialize;
use function is_scalar;
use function is_string;
use function spl_object_id;

/**
 * Class used to run async tasks in other threads.
 *
 * An AsyncTask is run by a thread pool of reusable threads, and doesn't have its own dedicated thread. A thread is
 * usually chosen from the pool at random to run the task (though a specific thread in the pool may be selected
 * manually, if needed).
 * Reusing threads this way has a much lower performance cost than starting an entirely new thread for every operation.
 * AsyncTasks are therefore suitable for brief CPU-bound tasks, such as world generation, compression/decompression of
 * data, etc.
 *
 * AsyncTask SHOULD NOT be used for I/O-bound tasks, such as network I/O, file I/O, database I/O, etc. The server's
 * central AsyncPool is used for things like compressing network packets for sending, so using AsyncTask for I/O will
 * slow the whole server down, stall chunk loading, etc.
 *
 * An AsyncTask SHOULD NOT run for more than a few seconds. For tasks that run for a long time or indefinitely, create
 * a dedicated thread instead.
 *
 * The Server instance is not accessible inside {@link AsyncTask::onRun()}. It can only be accessed in the main server
 * thread, e.g. during {@link AsyncTask::onCompletion()} or {@link AsyncTask::onProgressUpdate()}. This means that
 * whatever you do in onRun() must be able to work without the Server instance.
 *
 * WARNING: Any non-Threaded objects WILL BE SERIALIZED when assigned to members of AsyncTasks or other Threaded object.
 * If later accessed from said Threaded object, you will be operating on a COPY OF THE OBJECT, NOT THE ORIGINAL OBJECT.
 * If you want to store non-serializable objects to access when the task completes, store them using
 * {@link AsyncTask::storeLocal}.
 *
 * WARNING: Arrays are converted to Volatile objects when assigned as members of Threaded objects.
 * Keep this in mind when using arrays stored as members of your AsyncTask.
 */
abstract class AsyncTask extends \Threaded{
	/**
	 * @var \ArrayObject|mixed[]|null object hash => mixed data
	 * @phpstan-var \ArrayObject<int, array<string, mixed>>|null
	 *
	 * Used to store objects which are only needed on one thread and should not be serialized.
	 */
	private static ?\ArrayObject $threadLocalStorage = null;

	/** @var AsyncWorker|null $worker */
	public $worker = null;

	/** @var \Threaded */
	public $progressUpdates;

	private string|int|bool|null|float $result = null;
	private bool $serialized = false;
	private bool $cancelRun = false;
	private bool $submitted = false;

	private bool $crashed = false;
	private bool $finished = false;

	public function run() : void{
		$this->result = null;

		if(!$this->cancelRun){
			try{
				$this->onRun();
			}catch(\Throwable $e){
				$this->crashed = true;
				$this->worker->handleException($e);
			}
		}

		$this->finished = true;
		$this->worker->getNotifier()->wakeupSleeper();
	}

	public function isCrashed() : bool{
		return $this->crashed || $this->isTerminated();
	}

	/**
	 * Returns whether this task has finished executing, whether successfully or not. This differs from isRunning()
	 * because it is not true prior to task execution.
	 */
	public function isFinished() : bool{
		return $this->finished || $this->isCrashed();
	}

	public function hasResult() : bool{
		return $this->result !== null;
	}

	/**
	 * @return mixed
	 */
	public function getResult(){
		if($this->serialized){
			if(!is_string($this->result)) throw new AssumptionFailedError("Result expected to be a serialized string");
			return igbinary_unserialize($this->result);
		}
		return $this->result;
	}

	/**
	 * @param mixed $result
	 */
	public function setResult($result) : void{
		$this->result = ($this->serialized = !is_scalar($result)) ? igbinary_serialize($result) : $result;
	}

	public function cancelRun() : void{
		$this->cancelRun = true;
	}

	public function hasCancelledRun() : bool{
		return $this->cancelRun;
	}

	public function setSubmitted() : void{
		$this->submitted = true;
	}

	public function isSubmitted() : bool{
		return $this->submitted;
	}

	/**
	 * Actions to execute when run
	 */
	abstract public function onRun() : void;

	/**
	 * Actions to execute when completed (on main thread)
	 * Implement this if you want to handle the data in your AsyncTask after it has been processed
	 */
	public function onCompletion() : void{

	}

	/**
	 * Call this method from {@link AsyncTask::onRun} (AsyncTask execution thread) to schedule a call to
	 * {@link AsyncTask::onProgressUpdate} from the main thread with the given progress parameter.
	 *
	 * @param mixed $progress A value that can be safely serialize()'ed.
	 */
	public function publishProgress($progress) : void{
		$this->progressUpdates[] = igbinary_serialize($progress);
	}

	/**
	 * @internal Only call from AsyncPool.php on the main thread
	 */
	public function checkProgressUpdates() : void{
		while($this->progressUpdates->count() !== 0){
			$progress = $this->progressUpdates->shift();
			$this->onProgressUpdate(igbinary_unserialize($progress));
		}
	}

	/**
	 * Called from the main thread after {@link AsyncTask::publishProgress} is called.
	 * All {@link AsyncTask::publishProgress} calls should result in {@link AsyncTask::onProgressUpdate} calls before
	 * {@link AsyncTask::onCompletion} is called.
	 *
	 * @param mixed $progress The parameter passed to {@link AsyncTask#publishProgress}. It is serialize()'ed
	 *                        and then unserialize()'ed, as if it has been cloned.
	 */
	public function onProgressUpdate($progress) : void{

	}

	/**
	 * Called from the main thread when the async task experiences an error during onRun(). Use this for things like
	 * promise rejection.
	 */
	public function onError() : void{

	}

	/**
	 * Saves mixed data in thread-local storage. Data stored using this storage is **only accessible from the thread it
	 * was stored on**. Data stored using this method will **not** be serialized.
	 * This can be used to store references to variables which you need later on on the same thread, but not others.
	 *
	 * For example, plugin references could be stored in the constructor of the async task (which is called on the main
	 * thread) using this, and then fetched in onCompletion() (which is also called on the main thread), without them
	 * becoming serialized.
	 *
	 * Scalar types can be stored directly in class properties instead of using this storage.
	 *
	 * Objects stored in this storage can be retrieved using fetchLocal() on the same thread that this method was called
	 * from.
	 *
	 * @param mixed $complexData the data to store
	 */
	protected function storeLocal(string $key, $complexData) : void{
		if(self::$threadLocalStorage === null){
			/*
			 * It's necessary to use an object (not array) here because pthreads is stupid. Non-default array statics
			 * will be inherited when task classes are copied to the worker thread, which would cause unwanted
			 * inheritance of primitive thread-locals, which we really don't want for various reasons.
			 * It won't try to inherit objects though, so this is the easiest solution.
			 */
			self::$threadLocalStorage = new \ArrayObject();
		}
		self::$threadLocalStorage[spl_object_id($this)][$key] = $complexData;
	}

	/**
	 * Retrieves data stored in thread-local storage.
	 *
	 * If you used storeLocal(), you can use this on the same thread to fetch data stored. This should be used during
	 * onProgressUpdate() and onCompletion() to fetch thread-local data stored on the parent thread.
	 *
	 * @return mixed
	 *
	 * @throws \InvalidArgumentException if no data were stored by this AsyncTask instance.
	 */
	protected function fetchLocal(string $key){
		$id = spl_object_id($this);
		if(self::$threadLocalStorage === null || !isset(self::$threadLocalStorage[$id][$key])){
			throw new \InvalidArgumentException("No matching thread-local data found on this thread");
		}

		return self::$threadLocalStorage[$id][$key];
	}

	final public function __destruct(){
		$this->reallyDestruct();
		if(self::$threadLocalStorage !== null && isset(self::$threadLocalStorage[$h = spl_object_id($this)])){
			//Beware changing this code!
			//This code may cause the GC to be triggered, causing destruction of other AsyncTasks (which may or may not
			//have been indirectly referenced by the TLS).
			//This may cause the code to be re-entered from a different context unexpectedly, causing a crash if handled
			//incorrectly.
			if(self::$threadLocalStorage->count() === 1){
				self::$threadLocalStorage = null;
			}else{
				unset(self::$threadLocalStorage[$h]);
			}
		}
	}

	/**
	 * Override this to do normal __destruct() cleanup from a child class.
	 */
	protected function reallyDestruct() : void{

	}
}