MDL-66925 cron: Add cli option to keep adhoc task runner alive

admin/tool/task/cli/adhoc_task.php

@@ -32,10 +32,13 @@
     [
         'execute' => false,
         'help' => false,
+        'keep-alive' => 0,
         'showsql' => false,
         'showdebugging' => false,
     ], [
         'h' => 'help',
+        'e' => 'execute',
+        'k' => 'keep-alive',
     ]
 );
 
@@ -45,19 +48,20 @@
 }
 
 if ($options['help'] or empty($options['execute'])) {
-    $help =
-"Scheduled cron tasks.
+    $help = <<<EOT
+Ad hoc cron tasks.
 
 Options:
---showsql             Show sql queries before they are executed
---showdebugging       Show developer level debugging information
---execute             Run all queued adhoc tasks
--h, --help            Print out this help
+ -h, --help                Print out this help
+     --showsql             Show sql queries before they are executed
+     --showdebugging       Show developer level debugging information
+ -e, --execute             Run all queued adhoc tasks
+ -k, --keep-alive=N        Keep this script alive for N seconds and poll for new adhoc tasks
 
 Example:
 \$sudo -u www-data /usr/bin/php admin/tool/task/cli/adhoc_task.php --execute
 
-";
+EOT;
 
     echo $help;
     die;
@@ -84,6 +88,9 @@
 if (empty($options['execute'])) {
     exit(0);
 }
+if (empty($options['keep-alive'])) {
+    $options['keep-alive'] = 0;
+}
 
 if (!empty($CFG->showcronsql)) {
     $DB->set_debug(true);
@@ -93,25 +100,52 @@
 }
 
 core_php_time_limit::raise();
-$starttime = microtime();
 
 // Increase memory limit.
 raise_memory_limit(MEMORY_EXTRA);
 
-// Emulate normal session - we use admin accoutn by default.
+// Emulate normal session - we use admin account by default.
 cron_setup_user();
 
 // Start output log.
-$timenow = time();
+$timestart = time();
+$timenow = $timestart;
+$finishtime = $timenow + (int)$options['keep-alive'];
 $humantimenow = date('r', $timenow);
 mtrace("Server Time: {$humantimenow}\n");
 
 // Run all adhoc tasks.
 $taskcount = 0;
-while (!\core\task\manager::static_caches_cleared_since($timenow) &&
-        $task = \core\task\manager::get_next_adhoc_task($timenow)) {
-    cron_run_inner_adhoc_task($task);
-    $taskcount++;
-    unset($task);
+$waiting = false;
+while (!\core\task\manager::static_caches_cleared_since($timestart)) {
+
+    $task = \core\task\manager::get_next_adhoc_task($timenow);
+
+    if ($task) {
+        if ($waiting) {
+            cli_writeln('');
+        }
+        $waiting = false;
+        cron_run_inner_adhoc_task($task);
+        $taskcount++;
+        unset($task);
+    } else {
+        if (time() > $finishtime) {
+            break;
+        }
+        if (!$waiting) {
+            cli_write('Waiting for more adhoc tasks to be queued ');
+        } else {
+            cli_write('.');
+        }
+        $waiting = true;
+        sleep(1);
+        $timenow = time();
+    }
+}
+if ($waiting) {
+    cli_writeln('');
 }
+
 mtrace("Ran {$taskcount} adhoc tasks found at {$humantimenow}");
+