MDL-75247 assignfeedback_editpdf: Requeue conversion task for polling

mod/assign/feedback/editpdf/classes/task/convert_submission.php

@@ -17,6 +17,7 @@
 namespace assignfeedback_editpdf\task;
 
 use core\task\adhoc_task;
+use core\task\manager;
 use assignfeedback_editpdf\document_services;
 use assignfeedback_editpdf\combined_document;
 use context_module;
@@ -60,18 +61,58 @@ public function execute() {
             }
         }
 
+        $conversionrequirespolling = false;
         foreach ($users as $userid) {
             mtrace('Converting submission for user id ' . $userid);
-            $combineddocument = document_services::get_combined_pdf_for_attempt($assign, $userid, $data->submissionattempt);
-            $status = $combineddocument->get_status();
-            if ($status == combined_document::STATUS_COMPLETE) {
-                document_services::get_page_images_for_attempt($assign, $userid, $data->submissionattempt, false);
-                document_services::get_page_images_for_attempt($assign, $userid, $data->submissionattempt, true);
 
-                mtrace('The document has been successfully converted');
-            } else {
-                throw new \coding_exception('Document conversion completed with status ' . $status);
+            // Note: Before MDL-71468, the scheduled task version of this
+            // task would stop attempting to poll the conversion after a
+            // configured number of attempts were made to poll it, see:
+            //
+            // mod/assign/feedback/editpdf/classes/task/convert_submissions.php@MOODLE_400_STABLE
+            //
+            // This means that currently this adhoc task, if it fails, will retry forever. But
+            // the fail-delay mechanism will ensure that it eventually only tries once per day.
+            //
+            // See MDL-75457 for details on re-implementing the conversionattemptlimit.
+            //
+            // Also note: This code must not be in a try/catch - an exception needs to be thrown to
+            // allow the task API to mark the task as failed and update its faildelay. Using
+            // manager::adhoc_task_failed in the catch block will not work, as the task API
+            // will later assume the task completed successfully (as no exception was thrown) and
+            // complete it (removing it from the adhoc task queue).
+            $combineddocument = document_services::get_combined_pdf_for_attempt($assign, $userid, $data->submissionattempt);
+            switch ($combineddocument->get_status()) {
+                case combined_document::STATUS_READY:
+                case combined_document::STATUS_READY_PARTIAL:
+                case combined_document::STATUS_PENDING_INPUT:
+                    // The document has not been converted yet or is somehow still ready.
+                    $conversionrequirespolling = true;
+                    continue 2;
+                case combined_document::STATUS_FAILED:
+                    // Although STATUS_FAILED indicates a "permanent error" it should be possible
+                    // in some cases to fix the underlying problem, allowing the conversion to
+                    // complete. So we throw an exception here, allowing the adhoc task to retry.
+                    //
+                    // Currently this can result in the task trying indefinitely (although it will
+                    // settle on trying once per day due to the faildelay exponential backoff)
+                    // however once the conversionattepmtlimit is re-implemented in MDL-75457 the
+                    // task will eventually get dropped.
+                    throw new \moodle_exception('documentcombinationfailed');
             }
+
+            document_services::get_page_images_for_attempt($assign, $userid, $data->submissionattempt, false);
+            document_services::get_page_images_for_attempt($assign, $userid, $data->submissionattempt, true);
+        }
+
+        if ($conversionrequirespolling) {
+            mtrace('Conversion still in progress. Requeueing self to check again.');
+            $task = new self;
+            $task->set_custom_data($data);
+            $task->set_next_run_time(time() + MINSECS);
+            manager::queue_adhoc_task($task);
+        } else {
+            mtrace('The document has been successfully converted');
         }
     }
 }