MDL-59594 cli: Introduce cli helpers for graceful exits

    \core\local\cli\shutdown::script_supports_graceful_exit();

    Sets up interception of exit signals and keep the script running.

    \core\local\cli\shutdown::should_gracefully_exit();

    Use this to check whether you should exit, often inside a long running loop.

lang/en/admin.php

@@ -120,6 +120,8 @@
 $string['cleanup'] = 'Cleanup';
 $string['clianswerno'] = 'n';
 $string['cliansweryes'] = 'y';
+$string['cliexitgraceful'] = 'Exiting gracefully, please wait ...';
+$string['cliexitnow'] = 'Exiting right NOW';
 $string['cliincorrectvalueerror'] = 'Error, incorrect value "{$a->value}" for "{$a->option}"';
 $string['cliincorrectvalueretry'] = 'Incorrect value, please retry';
 $string['clistatusdisabled'] = 'Status: disabled';

lib/classes/local/cli/shutdown.php

@@ -0,0 +1,81 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * CLI script shutdown helper class.
+ *
+ * @package    core
+ * @copyright  2019 Brendan Heywood <brendan@catalyst-au.net>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+namespace core\local\cli;
+
+defined('MOODLE_INTERNAL') || die();
+
+/**
+ * CLI script shutdown helper class.
+ *
+ * @package    core
+ * @copyright  2019 Brendan Heywood <brendan@catalyst-au.net>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class shutdown {
+
+    /** @var bool Should we exit gracefully at the next opportunity? */
+    protected static $cligracefulexit = false;
+
+    /**
+     * Declares that this CLI script can gracefully handle signals
+     *
+     * @return void
+     */
+    public static function script_supports_graceful_exit(): void {
+        \core_shutdown_manager::register_signal_handler('\core\local\cli\shutdown::signal_handler');
+    }
+
+    /**
+     * Should we gracefully exit?
+     *
+     * @return bool true if we should gracefully exit
+     */
+    public static function should_gracefully_exit(): bool {
+        return self::$cligracefulexit;
+    }
+
+    /**
+     * Handle the signal
+     *
+     * The first signal flags a graceful exit. If a second signal is received
+     * then it immediately exits.
+     *
+     * @param int $signo The signal number
+     * @return bool true if we should exit
+     */
+    public static function signal_handler(int $signo): bool {
+
+        if (self::$cligracefulexit) {
+            cli_heading(get_string('cliexitnow', 'admin'));
+            return true;
+        }
+
+        cli_heading(get_string('cliexitgraceful', 'admin'));
+        self::$cligracefulexit = true;
+        return false;
+    }
+
+}
+