friendica/include/poller.php

<?php

use Friendica\App;
use Friendica\Core\System;
use Friendica\Core\Config;
use Friendica\Util\Lock;

if (!file_exists("boot.php") && (sizeof($_SERVER["argv"]) != 0)) {
	$directory = dirname($_SERVER["argv"][0]);

	if (substr($directory, 0, 1) != "/") {
		$directory = $_SERVER["PWD"]."/".$directory;
	}
	$directory = realpath($directory."/..");

	chdir($directory);
}

require_once("boot.php");

function poller_run($argv, $argc){
	global $a, $db, $poller_up_start, $poller_db_duration;

	$poller_up_start = microtime(true);

	$a = new App(dirname(__DIR__));

	@include(".htconfig.php");
	require_once("include/dba.php");
	$db = new dba($db_host, $db_user, $db_pass, $db_data);
	unset($db_host, $db_user, $db_pass, $db_data);

	Config::load();

	// Quit when in maintenance
	if (Config::get('system', 'maintenance', true)) {
		return;
	}

	$a->set_baseurl(Config::get('system', 'url'));

	load_hooks();

	// At first check the maximum load. We shouldn't continue with a high load
	if ($a->maxload_reached()) {
		logger('Pre check: maximum load reached, quitting.', LOGGER_DEBUG);
		return;
	}

	// We now start the process. This is done after the load check since this could increase the load.
	$a->start_process();

	// Kill stale processes every 5 minutes
	$last_cleanup = Config::get('system', 'poller_last_cleaned', 0);
	if (time() > ($last_cleanup + 300)) {
		Config::set('system', 'poller_last_cleaned', time());
		poller_kill_stale_workers();
	}

	// Count active workers and compare them with a maximum value that depends on the load
	if (poller_too_much_workers()) {
		logger('Pre check: Active worker limit reached, quitting.', LOGGER_DEBUG);
		return;
	}

	// Do we have too few memory?
	if ($a->min_memory_reached()) {
		logger('Pre check: Memory limit reached, quitting.', LOGGER_DEBUG);
		return;
	}

	// Possibly there are too much database connections
	if (poller_max_connections_reached()) {
		logger('Pre check: maximum connections reached, quitting.', LOGGER_DEBUG);
		return;
	}

	// Possibly there are too much database processes that block the system
	if ($a->max_processes_reached()) {
		logger('Pre check: maximum processes reached, quitting.', LOGGER_DEBUG);
		return;
	}

	// Now we start additional cron processes if we should do so
	if (($argc <= 1) || ($argv[1] != "no_cron")) {
		poller_run_cron();
	}

	$starttime = time();

	// We fetch the next queue entry that is about to be executed
	while ($r = poller_worker_process($passing_slow)) {

		// When we are processing jobs with a lower priority, we don't refetch new jobs
		// Otherwise fast jobs could wait behind slow ones and could be blocked.
		$refetched = $passing_slow;

		foreach ($r AS $entry) {
			// Assure that the priority is an integer value
			$entry['priority'] = (int)$entry['priority'];

			// The work will be done
			if (!poller_execute($entry)) {
				logger('Process execution failed, quitting.', LOGGER_DEBUG);
				return;
			}

			// If possible we will fetch new jobs for this worker
			if (!$refetched && Lock::set('poller_worker_process', 0)) {
				$stamp = (float)microtime(true);
				$refetched = find_worker_processes($passing_slow);
				$poller_db_duration += (microtime(true) - $stamp);
				Lock::remove('poller_worker_process');
			}
		}

		// To avoid the quitting of multiple pollers only one poller at a time will execute the check
		if (Lock::set('poller_worker', 0)) {
			$stamp = (float)microtime(true);
			// Count active workers and compare them with a maximum value that depends on the load
			if (poller_too_much_workers()) {
				logger('Active worker limit reached, quitting.', LOGGER_DEBUG);
				return;
			}

			// Check free memory
			if ($a->min_memory_reached()) {
				logger('Memory limit reached, quitting.', LOGGER_DEBUG);
				return;
			}
			Lock::remove('poller_worker');
			$poller_db_duration += (microtime(true) - $stamp);
		}

		// Quit the poller once every 5 minutes
		if (time() > ($starttime + 300)) {
			logger('Process lifetime reached, quitting.', LOGGER_DEBUG);
			return;
		}
	}
	logger("Couldn't select a workerqueue entry, quitting.", LOGGER_DEBUG);
}

/**
 * @brief Returns the number of non executed entries in the worker queue
 *
 * @return integer Number of non executed entries in the worker queue
 */
function poller_total_entries() {
	$s = q("SELECT COUNT(*) AS `total` FROM `workerqueue` WHERE `executed` <= '%s' AND NOT `done`", dbesc(NULL_DATE));
	if (dbm::is_result($s)) {
		return $s[0]["total"];
	} else {
		return 0;
	}
}

/**
 * @brief Returns the highest priority in the worker queue that isn't executed
 *
 * @return integer Number of active poller processes
 */
function poller_highest_priority() {
	$s = q("SELECT `priority` FROM `workerqueue` WHERE `executed` <= '%s' AND NOT `done` ORDER BY `priority` LIMIT 1", dbesc(NULL_DATE));
	if (dbm::is_result($s)) {
		return $s[0]["priority"];
	} else {
		return 0;
	}
}

/**
 * @brief Returns if a process with the given priority is running
 *
 * @param integer $priority The priority that should be checked
 *
 * @return integer Is there a process running with that priority?
 */
function poller_process_with_priority_active($priority) {
	$s = q("SELECT `id` FROM `workerqueue` WHERE `priority` <= %d AND `executed` > '%s' AND NOT `done` LIMIT 1",
			intval($priority), dbesc(NULL_DATE));
	return dbm::is_result($s);
}

/**
 * @brief Execute a worker entry
 *
 * @param array $queue Workerqueue entry
 *
 * @return boolean "true" if further processing should be stopped
 */
function poller_execute($queue) {
	global $poller_db_duration, $poller_last_update;

	$a = get_app();

	$mypid = getmypid();

	// Quit when in maintenance
	if (Config::get('system', 'maintenance', true)) {
		logger("Maintenance mode - quit process ".$mypid, LOGGER_DEBUG);
		return false;
	}

	// Constantly check the number of parallel database processes
	if ($a->max_processes_reached()) {
		logger("Max processes reached for process ".$mypid, LOGGER_DEBUG);
		return false;
	}

	// Constantly check the number of available database connections to let the frontend be accessible at any time
	if (poller_max_connections_reached()) {
		logger("Max connection reached for process ".$mypid, LOGGER_DEBUG);
		return false;
	}

	$argv = json_decode($queue["parameter"]);

	// Check for existance and validity of the include file
	$include = $argv[0];

	if (!validate_include($include)) {
		logger("Include file ".$argv[0]." is not valid!");
		dba::delete('workerqueue', array('id' => $queue["id"]));
		return true;
	}

	require_once($include);

	$funcname = str_replace(".php", "", basename($argv[0]))."_run";

	if (function_exists($funcname)) {

		// We constantly update the "executed" date every minute to avoid being killed too soon
		if (!isset($poller_last_update)) {
			$poller_last_update = strtotime($queue["executed"]);
		}

		$age = (time() - $poller_last_update) / 60;
		$poller_last_update = time();

		if ($age > 1) {
			$stamp = (float)microtime(true);
			dba::update('workerqueue', array('executed' => datetime_convert()), array('pid' => $mypid, 'done' => false));
			$poller_db_duration += (microtime(true) - $stamp);
		}

		poller_exec_function($queue, $funcname, $argv);

		$stamp = (float)microtime(true);
		if (dba::update('workerqueue', array('done' => true), array('id' => $queue["id"]))) {
			Config::set('system', 'last_poller_execution', datetime_convert());
		}
		$poller_db_duration = (microtime(true) - $stamp);
	} else {
		logger("Function ".$funcname." does not exist");
		dba::delete('workerqueue', array('id' => $queue["id"]));
	}

	return true;
}

/**
 * @brief Execute a function from the queue
 *
 * @param array $queue Workerqueue entry
 * @param string $funcname name of the function
 * @param array $argv Array of values to be passed to the function
 */
function poller_exec_function($queue, $funcname, $argv) {
	global $poller_up_start, $poller_db_duration, $poller_lock_duration;

	$a = get_app();

	$mypid = getmypid();

	$argc = count($argv);

	$new_process_id = uniqid("wrk", true);

	logger("Process ".$mypid." - Prio ".$queue["priority"]." - ID ".$queue["id"].": ".$funcname." ".$queue["parameter"]." - Process PID: ".$new_process_id);

	$stamp = (float)microtime(true);

	// We use the callstack here to analyze the performance of executed worker entries.
	// For this reason the variables have to be initialized.
	if (Config::get("system", "profiler")) {
		$a->performance["start"] = microtime(true);
		$a->performance["database"] = 0;
		$a->performance["database_write"] = 0;
		$a->performance["network"] = 0;
		$a->performance["file"] = 0;
		$a->performance["rendering"] = 0;
		$a->performance["parser"] = 0;
		$a->performance["marktime"] = 0;
		$a->performance["markstart"] = microtime(true);
		$a->callstack = array();
	}

	// For better logging create a new process id for every worker call
	// But preserve the old one for the worker
	$old_process_id = $a->process_id;
	$a->process_id = $new_process_id;
	$a->queue = $queue;

	$up_duration = number_format(microtime(true) - $poller_up_start, 3);

	// Reset global data to avoid interferences
	unset($_SESSION);

	$funcname($argv, $argc);

	$a->process_id = $old_process_id;
	unset($a->queue);

	$duration = number_format(microtime(true) - $stamp, 3);

	$poller_up_start = microtime(true);

	/* With these values we can analyze how effective the worker is.
	 * The database and rest time should be low since this is the unproductive time.
	 * The execution time is the productive time.
	 * By changing parameters like the maximum number of workers we can check the effectivness.
	*/
	logger('DB: '.number_format($poller_db_duration, 2).
		' - Lock: '.number_format($poller_lock_duration, 2).
		' - Rest: '.number_format($up_duration - $poller_db_duration - $poller_lock_duration, 2).
		' - Execution: '.number_format($duration, 2), LOGGER_DEBUG);
	$poller_lock_duration = 0;

	if ($duration > 3600) {
		logger("Prio ".$queue["priority"].": ".$queue["parameter"]." - longer than 1 hour (".round($duration/60, 3).")", LOGGER_DEBUG);
	} elseif ($duration > 600) {
		logger("Prio ".$queue["priority"].": ".$queue["parameter"]." - longer than 10 minutes (".round($duration/60, 3).")", LOGGER_DEBUG);
	} elseif ($duration > 300) {
		logger("Prio ".$queue["priority"].": ".$queue["parameter"]." - longer than 5 minutes (".round($duration/60, 3).")", LOGGER_DEBUG);
	} elseif ($duration > 120) {
		logger("Prio ".$queue["priority"].": ".$queue["parameter"]." - longer than 2 minutes (".round($duration/60, 3).")", LOGGER_DEBUG);
	}

	logger("Process ".$mypid." - Prio ".$queue["priority"]." - ID ".$queue["id"].": ".$funcname." - done in ".$duration." seconds. Process PID: ".$new_process_id);

	// Write down the performance values into the log
	if (Config::get("system", "profiler")) {
		$duration = microtime(true)-$a->performance["start"];

		if (Config::get("rendertime", "callstack")) {
			if (isset($a->callstack["database"])) {
				$o = "\nDatabase Read:\n";
				foreach ($a->callstack["database"] AS $func => $time) {
					$time = round($time, 3);
					if ($time > 0) {
						$o .= $func.": ".$time."\n";
					}
				}
			}
			if (isset($a->callstack["database_write"])) {
				$o .= "\nDatabase Write:\n";
				foreach ($a->callstack["database_write"] AS $func => $time) {
					$time = round($time, 3);
					if ($time > 0) {
						$o .= $func.": ".$time."\n";
					}
				}
			}
			if (isset($a->callstack["network"])) {
				$o .= "\nNetwork:\n";
				foreach ($a->callstack["network"] AS $func => $time) {
					$time = round($time, 3);
					if ($time > 0) {
						$o .= $func.": ".$time."\n";
					}
				}
			}
		} else {
			$o = '';
		}

		logger("ID ".$queue["id"].": ".$funcname.": ".sprintf("DB: %s/%s, Net: %s, I/O: %s, Other: %s, Total: %s".$o,
			number_format($a->performance["database"] - $a->performance["database_write"], 2),
			number_format($a->performance["database_write"], 2),
			number_format($a->performance["network"], 2),
			number_format($a->performance["file"], 2),
			number_format($duration - ($a->performance["database"] + $a->performance["network"] + $a->performance["file"]), 2),
			number_format($duration, 2)),
			LOGGER_DEBUG);
	}

	$cooldown = Config::get("system", "worker_cooldown", 0);

	if ($cooldown > 0) {
		logger("Process ".$mypid." - Prio ".$queue["priority"]." - ID ".$queue["id"].": ".$funcname." - in cooldown for ".$cooldown." seconds");
		sleep($cooldown);
	}
}

/**
 * @brief Checks if the number of database connections has reached a critical limit.
 *
 * @return bool Are more than 3/4 of the maximum connections used?
 */
function poller_max_connections_reached() {

	// Fetch the max value from the config. This is needed when the system cannot detect the correct value by itself.
	$max = Config::get("system", "max_connections");

	// Fetch the percentage level where the poller will get active
	$maxlevel = Config::get("system", "max_connections_level", 75);

	if ($max == 0) {
		// the maximum number of possible user connections can be a system variable
		$r = q("SHOW VARIABLES WHERE `variable_name` = 'max_user_connections'");
		if (dbm::is_result($r)) {
			$max = $r[0]["Value"];
		}
		// Or it can be granted. This overrides the system variable
		$r = q("SHOW GRANTS");
		if (dbm::is_result($r)) {
			foreach ($r AS $grants) {
				$grant = array_pop($grants);
				if (stristr($grant, "GRANT USAGE ON")) {
					if (preg_match("/WITH MAX_USER_CONNECTIONS (\d*)/", $grant, $match)) {
						$max = $match[1];
					}
				}
			}
		}
	}

	// If $max is set we will use the processlist to determine the current number of connections
	// The processlist only shows entries of the current user
	if ($max != 0) {
		$r = q("SHOW PROCESSLIST");
		if (!dbm::is_result($r)) {
			return false;
		}
		$used = count($r);

		logger("Connection usage (user values): ".$used."/".$max, LOGGER_DEBUG);

		$level = ($used / $max) * 100;

		if ($level >= $maxlevel) {
			logger("Maximum level (".$maxlevel."%) of user connections reached: ".$used."/".$max);
			return true;
		}
	}

	// We will now check for the system values.
	// This limit could be reached although the user limits are fine.
	$r = q("SHOW VARIABLES WHERE `variable_name` = 'max_connections'");
	if (!dbm::is_result($r)) {
		return false;
	}
	$max = intval($r[0]["Value"]);
	if ($max == 0) {
		return false;
	}
	$r = q("SHOW STATUS WHERE `variable_name` = 'Threads_connected'");
	if (!dbm::is_result($r)) {
		return false;
	}
	$used = intval($r[0]["Value"]);
	if ($used == 0) {
		return false;
	}
	logger("Connection usage (system values): ".$used."/".$max, LOGGER_DEBUG);

	$level = $used / $max * 100;

	if ($level < $maxlevel) {
		return false;
	}
	logger("Maximum level (".$level."%) of system connections reached: ".$used."/".$max);
	return true;
}

/**
 * @brief fix the queue entry if the worker process died
 *
 */
function poller_kill_stale_workers() {
	$entries = dba::select('workerqueue', array('id', 'pid', 'executed', 'priority', 'parameter'),
				array('`executed` > ? AND NOT `done` AND `pid` != 0', NULL_DATE),
				array('order' => array('priority', 'created')));
	while ($entry = dba::fetch($entries)) {
		if (!posix_kill($entry["pid"], 0)) {
			dba::update('workerqueue', array('executed' => NULL_DATE, 'pid' => 0),
					array('id' => $entry["id"]));
		} else {
			// Kill long running processes
			// Check if the priority is in a valid range
			if (!in_array($entry["priority"], array(PRIORITY_CRITICAL, PRIORITY_HIGH, PRIORITY_MEDIUM, PRIORITY_LOW, PRIORITY_NEGLIGIBLE))) {
				$entry["priority"] = PRIORITY_MEDIUM;
			}

			// Define the maximum durations
			$max_duration_defaults = array(PRIORITY_CRITICAL => 720, PRIORITY_HIGH => 10, PRIORITY_MEDIUM => 60, PRIORITY_LOW => 180, PRIORITY_NEGLIGIBLE => 720);
			$max_duration = $max_duration_defaults[$entry["priority"]];

			$argv = json_decode($entry["parameter"]);
			$argv[0] = basename($argv[0]);

			// How long is the process already running?
			$duration = (time() - strtotime($entry["executed"])) / 60;
			if ($duration > $max_duration) {
				logger("Worker process ".$entry["pid"]." (".implode(" ", $argv).") took more than ".$max_duration." minutes. It will be killed now.");
				posix_kill($entry["pid"], SIGTERM);

				// We killed the stale process.
				// To avoid a blocking situation we reschedule the process at the beginning of the queue.
				// Additionally we are lowering the priority. (But not PRIORITY_CRITICAL)
				if ($entry["priority"] == PRIORITY_HIGH) {
					$new_priority = PRIORITY_MEDIUM;
				} elseif ($entry["priority"] == PRIORITY_MEDIUM) {
					$new_priority = PRIORITY_LOW;
				} elseif ($entry["priority"] != PRIORITY_CRITICAL) {
					$new_priority = PRIORITY_NEGLIGIBLE;
				}
				dba::update('workerqueue',
						array('executed' => NULL_DATE, 'created' => datetime_convert(), 'priority' => $new_priority, 'pid' => 0),
						array('id' => $entry["id"]));
			} else {
				logger("Worker process ".$entry["pid"]." (".implode(" ", $argv).") now runs for ".round($duration)." of ".$max_duration." allowed minutes. That's okay.", LOGGER_DEBUG);
			}
		}
	}
}

/**
 * @brief Checks if the number of active workers exceeds the given limits
 *
 * @return bool Are there too much workers running?
 */
function poller_too_much_workers() {
	$queues = Config::get("system", "worker_queues", 4);

	$maxqueues = $queues;

	$active = poller_active_workers();

	// Decrease the number of workers at higher load
	$load = current_load();
	if ($load) {
		$maxsysload = intval(Config::get("system", "maxloadavg", 50));

		$maxworkers = $queues;

		// Some magical mathemathics to reduce the workers
		$exponent = 3;
		$slope = $maxworkers / pow($maxsysload, $exponent);
		$queues = ceil($slope * pow(max(0, $maxsysload - $load), $exponent));

		if (Config::get('system', 'worker_debug')) {
			// Create a list of queue entries grouped by their priority
			$listitem = array();

			// Adding all processes with no workerqueue entry
			$processes = dba::p("SELECT COUNT(*) AS `running` FROM `process` WHERE NOT EXISTS
						(SELECT id FROM `workerqueue`
						WHERE `workerqueue`.`pid` = `process`.`pid` AND NOT `done` AND `pid` != ?)", getmypid());
			if ($process = dba::fetch($processes)) {
				$listitem[0] = "0:".$process["running"];
			}
			dba::close($processes);

			// Now adding all processes with workerqueue entries
			$entries = dba::p("SELECT COUNT(*) AS `entries`, `priority` FROM `workerqueue` WHERE NOT `done` GROUP BY `priority`");
			while ($entry = dba::fetch($entries)) {
				$processes = dba::p("SELECT COUNT(*) AS `running` FROM `process` INNER JOIN `workerqueue` ON `workerqueue`.`pid` = `process`.`pid` AND NOT `done` WHERE `priority` = ?", $entry["priority"]);
				if ($process = dba::fetch($processes)) {
					$listitem[$entry["priority"]] = $entry["priority"].":".$process["running"]."/".$entry["entries"];
				}
				dba::close($processes);
			}
			dba::close($entries);

			$intervals = array(1, 10, 60);
			$jobs_per_minute = array();
			foreach ($intervals AS $interval) {
				$jobs = dba::p("SELECT COUNT(*) AS `jobs` FROM `workerqueue` WHERE `done` AND `executed` > UTC_TIMESTAMP() - INTERVAL ".intval($interval)." MINUTE");
				if ($job = dba::fetch($jobs)) {
					$jobs_per_minute[$interval] = number_format($job['jobs'] / $interval, 0);
				}
				dba::close($jobs);
			}
			$processlist = ' - jpm: '.implode('/', $jobs_per_minute).' ('.implode(', ', $listitem).')';
		}

		$entries = poller_total_entries();

		if (Config::get("system", "worker_fastlane", false) && ($queues > 0) && ($entries > 0) && ($active >= $queues)) {
			$top_priority = poller_highest_priority();
			$high_running = poller_process_with_priority_active($top_priority);

			if (!$high_running && ($top_priority > PRIORITY_UNDEFINED) && ($top_priority < PRIORITY_NEGLIGIBLE)) {
				logger("There are jobs with priority ".$top_priority." waiting but none is executed. Open a fastlane.", LOGGER_DEBUG);
				$queues = $active + 1;
			}
		}

		logger("Load: ".$load."/".$maxsysload." - processes: ".$active."/".$entries.$processlist." - maximum: ".$queues."/".$maxqueues, LOGGER_DEBUG);

		// Are there fewer workers running as possible? Then fork a new one.
		if (!Config::get("system", "worker_dont_fork") && ($queues > ($active + 1)) && ($entries > 1)) {
			logger("Active workers: ".$active."/".$queues." Fork a new worker.", LOGGER_DEBUG);
			$args = array("include/poller.php", "no_cron");
			get_app()->proc_run($args);
		}
	}

	return $active >= $queues;
}

/**
 * @brief Returns the number of active poller processes
 *
 * @return integer Number of active poller processes
 */
function poller_active_workers() {
	$workers = q("SELECT COUNT(*) AS `processes` FROM `process` WHERE `command` = 'poller.php'");

	return $workers[0]["processes"];
}

/**
 * @brief Check if we should pass some slow processes
 *
 * When the active processes of the highest priority are using more than 2/3
 * of all processes, we let pass slower processes.
 *
 * @param string $highest_priority Returns the currently highest priority
 * @return bool We let pass a slower process than $highest_priority
 */
function poller_passing_slow(&$highest_priority) {

	$highest_priority = 0;

	$r = q("SELECT `priority`
		FROM `process`
		INNER JOIN `workerqueue` ON `workerqueue`.`pid` = `process`.`pid` AND NOT `done`");

	// No active processes at all? Fine
	if (!dbm::is_result($r)) {
		return false;
	}
	$priorities = array();
	foreach ($r AS $line) {
		$priorities[] = $line["priority"];
	}
	// Should not happen
	if (count($priorities) == 0) {
		return false;
	}
	$highest_priority = min($priorities);

	// The highest process is already the slowest one?
	// Then we quit
	if ($highest_priority == PRIORITY_NEGLIGIBLE) {
		return false;
	}
	$high = 0;
	foreach ($priorities AS $priority) {
		if ($priority == $highest_priority) {
			++$high;
		}
	}
	logger("Highest priority: ".$highest_priority." Total processes: ".count($priorities)." Count high priority processes: ".$high, LOGGER_DEBUG);
	$passing_slow = (($high/count($priorities)) > (2/3));

	if ($passing_slow) {
		logger("Passing slower processes than priority ".$highest_priority, LOGGER_DEBUG);
	}
	return $passing_slow;
}

/**
 * @brief Find and claim the next worker process for us
 *
 * @param boolean $passing_slow Returns if we had passed low priority processes
 * @return boolean Have we found something?
 */
function find_worker_processes(&$passing_slow) {

	$mypid = getmypid();

	// Check if we should pass some low priority process
	$highest_priority = 0;
	$found = false;
	$passing_slow = false;

	// The higher the number of parallel workers, the more we prefetch to prevent concurring access
	// We decrease the limit with the number of entries left in the queue
	$worker_queues = Config::get("system", "worker_queues", 4);
	$queue_length = Config::get('system', 'worker_fetch_limit', 1);
	$lower_job_limit = $worker_queues * $queue_length * 2;
	$jobs = poller_total_entries();

	// Now do some magic
	$exponent = 2;
	$slope = $queue_length / pow($lower_job_limit, $exponent);
	$limit = min($queue_length, ceil($slope * pow($jobs, $exponent)));

	logger('Total: '.$jobs.' - Maximum: '.$queue_length.' - jobs per queue: '.$limit, LOGGER_DEBUG);

	if (poller_passing_slow($highest_priority)) {
		// Are there waiting processes with a higher priority than the currently highest?
		$result = dba::select('workerqueue', array('id'), array("`executed` <= ? AND `priority` < ? AND NOT `done`", NULL_DATE, $highest_priority),
				array('limit' => $limit, 'order' => array('priority', 'created'), 'only_query' => true));

		while ($id = dba::fetch($result)) {
			$ids[] = $id["id"];
		}
		dba::close($result);

		$found = (count($ids) > 0);

		if (!$found) {
			// Give slower processes some processing time
			$result = dba::select('workerqueue', array('id'), array("`executed` <= ? AND `priority` > ? AND NOT `done`", NULL_DATE, $highest_priority),
					array('limit' => $limit, 'order' => array('priority', 'created'), 'only_query' => true));

			while ($id = dba::fetch($result)) {
				$ids[] = $id["id"];
			}
			dba::close($result);

			$found = (count($ids) > 0);
			$passing_slow = $found;
		}
	}

	// If there is no result (or we shouldn't pass lower processes) we check without priority limit
	if (!$found) {
		$result = dba::select('workerqueue', array('id'), array("`executed` <= ? AND NOT `done`", NULL_DATE),
				array('limit' => $limit, 'order' => array('priority', 'created'), 'only_query' => true));

		while ($id = dba::fetch($result)) {
			$ids[] = $id["id"];
		}
		dba::close($result);

		$found = (count($ids) > 0);
	}

	if ($found) {
		$condition = "`id` IN (".substr(str_repeat("?, ", count($ids)), 0, -2).") AND `pid` = 0 AND NOT `done`";
		array_unshift($ids, $condition);
		dba::update('workerqueue', array('executed' => datetime_convert(), 'pid' => $mypid), $ids);
	}

	return $found;
}

/**
 * @brief Returns the next worker process
 *
 * @param boolean $passing_slow Returns if we had passed low priority processes
 * @return string SQL statement
 */
function poller_worker_process(&$passing_slow) {
	global $poller_db_duration, $poller_lock_duration;

	$stamp = (float)microtime(true);

	// There can already be jobs for us in the queue.
	$r = q("SELECT * FROM `workerqueue` WHERE `pid` = %d AND NOT `done`", intval(getmypid()));
	if (dbm::is_result($r)) {
		$poller_db_duration += (microtime(true) - $stamp);
		return $r;
	}

	$stamp = (float)microtime(true);
	if (!Lock::set('poller_worker_process')) {
		return false;
	}
	$poller_lock_duration = (microtime(true) - $stamp);

	$stamp = (float)microtime(true);
	$found = find_worker_processes($passing_slow);
	$poller_db_duration += (microtime(true) - $stamp);

	Lock::remove('poller_worker_process');

	if ($found) {
		$r = q("SELECT * FROM `workerqueue` WHERE `pid` = %d AND NOT `done`", intval(getmypid()));
	}
	return $r;
}

/**
 * @brief Removes a workerqueue entry from the current process
 */
function poller_unclaim_process() {
	$mypid = getmypid();

	dba::update('workerqueue', array('executed' => NULL_DATE, 'pid' => 0), array('pid' => $mypid, 'done' => false));
}

/**
 * @brief Call the front end worker
 */
function call_worker() {
	if (!Config::get("system", "frontend_worker")) {
		return;
	}

	$url = System::baseUrl()."/worker";
	fetch_url($url, false, $redirects, 1);
}

/**
 * @brief Call the front end worker if there aren't any active
 */
function call_worker_if_idle() {
	if (!Config::get("system", "frontend_worker")) {
		return;
	}

	// Do we have "proc_open"? Then we can fork the poller
	if (function_exists("proc_open")) {
		// When was the last time that we called the worker?
		// Less than one minute? Then we quit
		if ((time() - Config::get("system", "worker_started")) < 60) {
			return;
		}

		set_config("system", "worker_started", time());

		// Do we have enough running workers? Then we quit here.
		if (poller_too_much_workers()) {
			// Cleaning dead processes
			poller_kill_stale_workers();
			get_app()->remove_inactive_processes();

			return;
		}

		poller_run_cron();

		logger('Call poller', LOGGER_DEBUG);

		$args = array("include/poller.php", "no_cron");
		get_app()->proc_run($args);
		return;
	}

	// We cannot execute background processes.
	// We now run the processes from the frontend.
	// This won't work with long running processes.
	poller_run_cron();

	clear_worker_processes();

	$workers = q("SELECT COUNT(*) AS `processes` FROM `process` WHERE `command` = 'worker.php'");

	if ($workers[0]["processes"] == 0) {
		call_worker();
	}
}

/**
 * @brief Removes long running worker processes
 */
function clear_worker_processes() {
	$timeout = Config::get("system", "frontend_worker_timeout", 10);

	/// @todo We should clean up the corresponding workerqueue entries as well
	q("DELETE FROM `process` WHERE `created` < '%s' AND `command` = 'worker.php'",
		dbesc(datetime_convert('UTC','UTC',"now - ".$timeout." minutes")));
}

/**
 * @brief Runs the cron processes
 */
function poller_run_cron() {
	logger('Add cron entries', LOGGER_DEBUG);

	// Check for spooled items
	proc_run(PRIORITY_HIGH, "include/spool_post.php");

	// Run the cron job that calls all other jobs
	proc_run(PRIORITY_MEDIUM, "include/cron.php");

	// Run the cronhooks job separately from cron for being able to use a different timing
	proc_run(PRIORITY_MEDIUM, "include/cronhooks.php");

	// Cleaning dead processes
	poller_kill_stale_workers();
}

if (array_search(__file__,get_included_files())===0) {
	// Check the database structure and possibly fixes it
	check_db(true);

	poller_run($_SERVER["argv"],$_SERVER["argc"]);

	poller_unclaim_process();

	get_app()->end_process();

	killme();
}