BUG: Doorman manager child processing fix. (#305)

* BUG: Doorman manager child processing fix.
* PR fixes
* Configurable behaviour (PR fixes).

composer.json

@@ -18,7 +18,7 @@
         "php": "^7.1",
         "silverstripe/framework": "^4.7",
         "silverstripe/admin": "^1",
-        "asyncphp/doorman": "^3.0"
+        "asyncphp/doorman": "^3.1"
     },
     "require-dev": {
         "sminnee/phpunit": "^5.7",

src/Services/ProcessManager.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace Symbiote\QueuedJobs\Services;
+
+use AsyncPHP\Doorman\Manager\ProcessManager as BaseProcessManager;
+use SilverStripe\Core\Config\Configurable;
+
+/**
+ * Class ProcessManager
+ *
+ * customise shell command to allow child tasks to persist even after manager process is terminated
+ * this lets the started jobs to finish properly in case the management process terminates
+ * fore example there are no more jobs to start or queue is paused
+ *
+ * @package Symbiote\QueuedJobs\Services
+ */
+class ProcessManager extends BaseProcessManager
+{
+    use Configurable;
+
+    /**
+     * Enable / disable persistent child process
+     * If this is enabled the child processes can outlive the parent (manager process)
+     * This is what is needed for most cases as the manager process only starts new child processes
+     * Child processes on the other hand, actually execute queued jobs so they may take longer to execute
+     * Disabling this may cause the child processes to terminate prematurely which may result it multiple job
+     * execution retries / resumes
+     * Disable this option only if you are debugging a situation when a child process
+     * keeps hanging around for way too long (hours)
+     * Adding execution timeout to individual queued jobs is recommended to avoid such situation
+     *
+     * @config
+     * @var bool
+     */
+    private static $persistent_child_process = true;
+
+    /**
+     * @param string $binary
+     * @param string $worker
+     * @param string $stdout
+     * @param string $stderr
+     * @return string
+     */
+    protected function getCommand($binary, $worker, $stdout, $stderr) // phpcs:ignore SlevomatCodingStandard.TypeHints
+    {
+        // Nohup is short for “No Hangups.” It’s not a command that you run by itself.
+        // Nohup is a supplemental command that tells the Linux system not to stop another command once it has started.
+        // That means it’ll keep running until it’s done, even if the user that started it logs out
+        // Nohup is used here because the queue management process runs in a loop and it's starting new child processes
+        // which are running jobs
+        // It's possible to have the situation when queue management process terminates as it's no longer needed
+        // to create any new child processes but we still want the existing child processes to continue their work
+        // and finish the jbos which are already running
+        return sprintf('nohup %s %s %%s %s %s & echo $!', $binary, $worker, $stdout, $stderr);
+    }
+
+    public function __destruct()
+    {
+        if ($this->config()->get('persistent_child_process')) {
+            // Prevent background tasks from being killed when this script finishes
+            // this is an override for the default behaviour of killing background tasks
+            return;
+        }
+
+        parent::__destruct();
+    }
+}

src/Tasks/Engines/DoormanRunner.php

@@ -2,12 +2,12 @@
 
 namespace Symbiote\QueuedJobs\Tasks\Engines;
 
-use AsyncPHP\Doorman\Manager\ProcessManager;
 use SilverStripe\Core\Environment;
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\ORM\FieldType\DBDatetime;
 use Symbiote\QueuedJobs\DataObjects\QueuedJobDescriptor;
 use Symbiote\QueuedJobs\Jobs\DoormanQueuedJobTask;
+use Symbiote\QueuedJobs\Services\ProcessManager;
 use Symbiote\QueuedJobs\Services\QueuedJob;
 use Symbiote\QueuedJobs\Services\QueuedJobService;