Test script to show how Elgg 1.8+ handles asynchronous parallel metadata updates.

parallel_test.php

<?php 

	require_once (dirname(__FILE__)) . '/engine/start.php';
	
	$options = array(
		'type' => 'object',
		'subtype' => 'paraleltest',
		'limit' => 1
	);
	
	$access = elgg_set_ignore_access(true);
	
	$entities = elgg_get_entities($options);

	if (is_array($entities) && !empty($entities)) {
		$entity = $entities[0];
		if (isset($entity->impressions)) {
			$entity->impressions = $entity->impressions + 1;
		} else {
			$entity->impressions = 1;
		}
		error_log("Counter is now {$entity->impressions}");
	} else {
		// Pick any user to be the owner of the object
		$users = elgg_get_entities(array('type' => 'user'));
		$user = $users[0];
		
		$object = new ElggObject();
		$object->subtype = 'paraleltest';
		$object->owner_guid = $user->guid;
		$object->container_guid = $user->guid;
		$object->access_id = ACCESS_PUBLIC;
		$object->save();
		
		$object->impressions = 0;
		$object->save();
		
		error_log("Test object created");
	}
	
	elgg_set_ignore_access($access);
?>

1. Drop this script into your Elgg installation's root directory.
2. Hit http://your-elgg-site/parallel_test.php in your browser a couple of times, and watch the log. Counter should increase one by one.
3. Run "ab -n 100 -c 10 http://your-elgg-site/parallel_test.php" and watch the log. You'll see at some point the integer property turning into an array.