New scheduler mechanism

src/Core/Worker.php

@@ -892,6 +892,85 @@ class Worker
 		return $passing_slow;
 	}
 
+	public static function nextProcess()
+	{
+		$priority = self::nextPriority();
+		if (empty($priority)) {
+			Logger::log('No tasks found', Logger::DEBUG);
+			return [];
+		}
+
+		if ($priority <= PRIORITY_MEDIUM) {
+			$limit = Config::get('system', 'worker_fetch_limit', 1);
+		} else {
+			$limit = 1;
+		}
+
+		$ids = [];
+		$stamp = (float)microtime(true);
+		$condition = ["`priority` = ? AND `pid` = 0 AND NOT `done` AND `next_try` < ?", $priority, DateTimeFormat::utcNow()];
+		$tasks = DBA::select('workerqueue', ['id'], $condition, ['limit' => $limit, 'order' => ['created']]);
+		self::$db_duration += (microtime(true) - $stamp);
+		while ($task = DBA::fetch($tasks)) {
+			$ids[] = $task['id'];
+		}
+		DBA::close($tasks);
+
+		Logger::log('Found task(s) ' . implode(', ', $ids) . ' with priority ' .$priority, Logger::DEBUG);
+		return $ids;
+	}
+
+	public static function nextPriority()
+	{
+		$waiting = [];
+		$priorities = [PRIORITY_CRITICAL, PRIORITY_HIGH, PRIORITY_MEDIUM, PRIORITY_LOW, PRIORITY_NEGLIGIBLE];
+		foreach ($priorities as $priority) {
+			$stamp = (float)microtime(true);
+			if (DBA::exists('workerqueue', ["`priority` = ? AND `pid` = 0 AND NOT `done` AND `next_try` < ?", $priority, DateTimeFormat::utcNow()])) {
+				$waiting[$priority] = true;
+			}
+			self::$db_duration += (microtime(true) - $stamp);
+		}
+
+		if (!empty($waiting[PRIORITY_CRITICAL])) {
+			return PRIORITY_CRITICAL;
+		}
+
+		$running = [];
+		$stamp = (float)microtime(true);
+		$processes = DBA::p("SELECT COUNT(DISTINCT(`process`.`pid`)) AS `running`, `priority` FROM `process`
+			INNER JOIN `workerqueue` ON `workerqueue`.`pid` = `process`.`pid`
+			WHERE NOT `done` GROUP BY `priority`");
+		self::$db_duration += (microtime(true) - $stamp);
+		while ($process = DBA::fetch($processes)) {
+			$running[$process['priority']] = $process['running'];
+		}
+		DBA::close($processes);
+
+		$active = self::activeWorkers();
+
+		foreach ($priorities as $priority) {
+			if (!empty($waiting[$priority]) && empty($running[$priority])) {
+				return $priority;
+			}
+		}
+
+		// Temp
+		if (!empty($running[PRIORITY_LOW]) && ($running[PRIORITY_LOW] < 3)) {
+			return PRIORITY_LOW;
+		}
+
+		if (!empty($running[PRIORITY_NEGLIGIBLE]) && ($running[PRIORITY_NEGLIGIBLE] < 2)) {
+			return PRIORITY_NEGLIGIBLE;
+		}
+
+		if (!empty($waiting)) {
+			return array_shift(array_keys($waiting));
+		}
+
+		return false;
+	}
+
 	/**
 	 * @brief Find and claim the next worker process for us
 	 *
@@ -923,8 +1002,11 @@ class Worker
 		$limit = min($queue_length, ceil($slope * pow($entries, $exponent)));
 
 		Logger::log('Deferred: ' . $deferred . ' - Total: ' . $entries . ' - Maximum: ' . $queue_length . ' - jobs per queue: ' . $limit, Logger::DEBUG);
-		$ids = [];
+
-		if (self::passingSlow($highest_priority)) {
+		$ids = self::nextProcess();
+		$found = (count($ids) > 0);
+
+		if (!$found && self::passingSlow($highest_priority)) {
 			// Are there waiting processes with a higher priority than the currently highest?
 			$stamp = (float)microtime(true);
 			$result = DBA::select(