Bugfix: The poller often couldn't store the pid in the workerqueue

include/poller.php

@@ -73,6 +73,10 @@ function poller_run($argv, $argc){
 
 	while ($r = poller_worker_process()) {
 
+		if (!poller_claim_process($r[0])) {
+			continue;
+		}
+
 		// Check free memory
 		if ($a->min_memory_reached()) {
 			return;
@@ -108,43 +112,22 @@ function poller_execute($queue) {
 
 	// 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;
 	}
 
-	if (!dba::update('workerqueue', array('executed' => datetime_convert(), 'pid' => $mypid),
-			array('id' => $queue["id"], 'pid' => 0))) {
-		logger("Couldn't update queue entry ".$queue["id"]." - skip this execution", LOGGER_DEBUG);
-		dba::commit();
-		return true;
-	}
-
-	// Assure that there are no tasks executed twice
-	$id = q("SELECT `pid`, `executed` FROM `workerqueue` WHERE `id` = %d", intval($queue["id"]));
-	if (!$id) {
-		logger("Queue item ".$queue["id"]." vanished - skip this execution", LOGGER_DEBUG);
-		dba::commit();
-		return true;
-	} elseif ((strtotime($id[0]["executed"]) <= 0) OR ($id[0]["pid"] == 0)) {
-		logger("Entry for queue item ".$queue["id"]." wasn't stored - skip this execution", LOGGER_DEBUG);
-		dba::commit();
-		return true;
-	} elseif ($id[0]["pid"] != $mypid) {
-		logger("Queue item ".$queue["id"]." is to be executed by process ".$id[0]["pid"]." and not by me (".$mypid.") - skip this execution", LOGGER_DEBUG);
-		dba::commit();
-		return true;
-	}
-	dba::commit();
-
 	$argv = json_decode($queue["parameter"]);
 
 	// Check for existance and validity of the include file
@@ -566,7 +549,7 @@ function poller_worker_process() {
 		// Are there waiting processes with a higher priority than the currently highest?
 		$r = q("SELECT * FROM `workerqueue`
 				WHERE `executed` <= '%s' AND `priority` < %d
-				ORDER BY `priority`, `created` LIMIT 1",
+				ORDER BY `priority`, `created` LIMIT 1 FOR UPDATE",
 				dbesc(NULL_DATE),
 				intval($highest_priority));
 		if (dbm::is_result($r)) {
@@ -575,18 +558,70 @@ function poller_worker_process() {
 		// Give slower processes some processing time
 		$r = q("SELECT * FROM `workerqueue`
 				WHERE `executed` <= '%s' AND `priority` > %d
-				ORDER BY `priority`, `created` LIMIT 1",
+				ORDER BY `priority`, `created` LIMIT 1 FOR UPDATE",
 				dbesc(NULL_DATE),
 				intval($highest_priority));
+
+		if (dbm::is_result($r)) {
+			return $r;
+		}
 	}
 
 	// If there is no result (or we shouldn't pass lower processes) we check without priority limit
-	if (($highest_priority == 0) OR !dbm::is_result($r)) {
+	if (!dbm::is_result($r)) {
-		$r = q("SELECT * FROM `workerqueue` WHERE `executed` <= '%s' ORDER BY `priority`, `created` LIMIT 1", dbesc(NULL_DATE));
+		$r = q("SELECT * FROM `workerqueue` WHERE `executed` <= '%s' ORDER BY `priority`, `created` LIMIT 1 FOR UPDATE", dbesc(NULL_DATE));
 	}
+
 	return $r;
 }
 
+/**
+ * @brief Assigns a workerqueue entry to the current process
+ *
+ * All the checks after the update are only needed with MyISAM.
+ *
+ * @param array $queue Workerqueue entry
+ *
+ * @return boolean "true" if the claiming was successful
+ */
+function poller_claim_process($queue) {
+	$mypid = getmypid();
+
+	if (!dba::update('workerqueue', array('executed' => datetime_convert(), 'pid' => $mypid),
+			array('id' => $queue["id"], 'pid' => 0))) {
+		logger("Couldn't update queue entry ".$queue["id"]." - skip this execution", LOGGER_DEBUG);
+		dba::commit();
+		return false;
+	}
+
+	// Assure that there are no tasks executed twice
+	$id = q("SELECT `pid`, `executed` FROM `workerqueue` WHERE `id` = %d", intval($queue["id"]));
+	if (!$id) {
+		logger("Queue item ".$queue["id"]." vanished - skip this execution", LOGGER_DEBUG);
+		dba::commit();
+		return false;
+	} elseif ((strtotime($id[0]["executed"]) <= 0) OR ($id[0]["pid"] == 0)) {
+		logger("Entry for queue item ".$queue["id"]." wasn't stored - skip this execution", LOGGER_DEBUG);
+		dba::commit();
+		return false;
+	} elseif ($id[0]["pid"] != $mypid) {
+		logger("Queue item ".$queue["id"]." is to be executed by process ".$id[0]["pid"]." and not by me (".$mypid.") - skip this execution", LOGGER_DEBUG);
+		dba::commit();
+		return false;
+	}
+	dba::commit();
+	return true;
+}
+
+/**
+ * @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' => $mypid));
+}
+
 /**
  * @brief Call the front end worker
  */
@@ -683,6 +718,8 @@ function poller_run_cron() {
 if (array_search(__file__,get_included_files())===0){
 	poller_run($_SERVER["argv"],$_SERVER["argc"]);
 
+	poller_unclaim_process();
+
 	get_app()->end_process();
 
 	killme();

mod/worker.php

@@ -41,11 +41,15 @@ function worker_init($a){
 		// But since it doesn't destroy anything, we just try to get more execution time in any way.
 		set_time_limit(0);
 
-		poller_execute($r[0]);
+		if (poller_claim_process($r[0])) {
+			poller_execute($r[0]);
+		}
 	}
 
 	call_worker();
 
+	poller_unclaim_process();
+
 	$a->end_process();
 
 	logger("Front end worker ended: ".getmypid());