PMThreads.php

<?php

class PocketMineInstance extends Thread{
	public $cwd;
	public $args;
	
	public function __construct($workingDirectory, $args){
		$this->cwd = realpath($workingDirectory) . "/";
		$this->args = $args;
		$this->start(PTHREADS_INHERIT_NONE);
	}
	
	public function run(){
		chdir($this->cwd);
		$argv = explode(" ", $args);
		arrat_unshift($argv, $this->cwd . "PocketMine-MP.php");
		$argc = count($args);
		require($this->cwd . "PocketMine-MP.php");
	}
}

//Warning: each instance MUST use a different port.

$instances = array(
	"folder/to/PocketMine/instance/" => "--argument=value --server-port=19132",
	"another/folder/to/PocketMine/instance/" => "--argument=value --server-port=19133",
);

$threads = array();

foreach($instances as $wd => $args){
	$threads[$wd] = new PocketMineInstance($wd, $args);
}