public function tearDown()
 {
     global $CFG;
     if (empty($CFG->keeptempdirectoriesonbackup)) {
         fulldelete("{$CFG->dataroot}/temp/backup/{$this->tempdir}");
     }
 }

 /**
  * Does any post-processing that may be desired
  * Clean the temporary directory if a zip file was imported
  * @return bool success
  */
 public function importpostprocess()
 {
     if ($this->tempdir != '') {
         fulldelete($this->tempdir);
     }
     return true;
 }

/**
 * Invalidate all server and client side caches.
 * @return void
 */
function theme_reset_all_caches() {
    global $CFG;
    require_once("$CFG->libdir/filelib.php");

    set_config('themerev', empty($CFG->themerev) ? 1 : $CFG->themerev+1);
    fulldelete("$CFG->dataroot/cache/theme");
}

function webquest_upgrade($oldversion)
{
    /// This function does anything necessary to upgrade
    /// older versions to match current functionality
    $status = true;
    global $CFG;
    if ($oldversion < 2007081222) {
        require_once $CFG->dirroot . '/backup/lib.php';
        //make the change into each course
        $courses = get_records("course");
        foreach ($courses as $course) {
            $newdir = "{$course->id}/{$CFG->moddata}/webquest";
            if (make_upload_directory($newdir)) {
                $olddir = "{$CFG->dataroot}/{$course->id}/{$CFG->moddata}/webquest/submissions";
                //chec k if the old directory exists
                if (is_dir($olddir)) {
                    $status = backup_copy_file($olddir, $CFG->dataroot . "/" . $newdir);
                }
                if ($status) {
                    fulldelete($olddir);
                }
            }
        }
    }
    return $status;
}

 protected function tearDown()
 {
     global $CFG;
     if (empty($CFG->keeptempdirectoriesonbackup)) {
         fulldelete("{$CFG->tempdir}/backup/{$this->tempdir}");
     }
 }

function delete_certificate_files($certificate = '')
{
    global $CFG;
    require_once $CFG->libdir . '/filelib.php';
    $dir = $CFG->dataroot . '/' . $certificate->course . '/' . $CFG->moddata . '/certificate/' . $certificate->id . '/' . $user->id;
    if ($certificateid) {
        $dir .= '/' . $certificateid;
    }
    return fulldelete($dir);
}

/**
 * Invalidate all server and client side caches.
 *
 * This method deletes the physical directory that is used to cache the theme
 * files used for serving.
 * Because it deletes the main theme cache directory all themes are reset by
 * this function.
 */
function theme_reset_all_caches()
{
    global $CFG;
    require_once "{$CFG->libdir}/filelib.php";
    $next = time();
    if (isset($CFG->themerev) and $next <= $CFG->themerev and $CFG->themerev - $next < 60 * 60) {
        // This resolves problems when reset is requested repeatedly within 1s,
        // the < 1h condition prevents accidental switching to future dates
        // because we might not recover from it.
        $next = $CFG->themerev + 1;
    }
    set_config('themerev', $next);
    // time is unique even when you reset/switch database
    fulldelete("{$CFG->cachedir}/theme");
}

function webquest_delete_instance($id)
{
    /// Given an ID of an instance of this module,
    /// delete the instance and any data that depends on it.
    global $CFG;
    if (!($webquest = get_record("webquest", "id", "{$id}"))) {
        return false;
    }
    $result = true;
    if (!delete_records("webquest", "id", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_resources", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_tasks", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_rubrics", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_grades", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_teams", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if (!delete_records("webquest_team_members", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    if ($submissions = get_records("webquest_submissions", "webquestid", "{$webquest->id}")) {
        foreach ($submissions as $submission) {
            $dirpath = "{$CFG->dataroot}/{$webquest->course}/{$CFG->moddata}/webquest/{$submission->id}";
            fulldelete($dirpath);
        }
    }
    if (!delete_records("webquest_submissions", "webquestid", "{$webquest->id}")) {
        $result = false;
    }
    return $result;
}

 public function execute()
 {
     global $CFG, $DB;
     if ($this->expandedOptions['flush']) {
         if (isset($CFG->trashdir)) {
             $trashdir = $CFG->trashdir;
         } else {
             $trashdir = $CFG->dataroot . '/trashdir';
         }
         require_once $CFG->libdir . '/filelib.php';
         fulldelete($trashdir);
         exit(0);
     }
     if ($this->expandedOptions['stdin']) {
         while ($line = fgets(STDIN)) {
             $this->fileDelete($line);
         }
     } else {
         foreach ($this->arguments as $argument) {
             $this->fileDelete($argument);
         }
     }
 }

 /**
  * Deletes an assignment activity
  *
  * Deletes all database records, files and calendar events for this assignment.
  * @param $assignment object The assignment to be deleted
  * @return boolean False indicates error
  */
 function delete_instance($assignment)
 {
     global $CFG;
     $assignment->courseid = $assignment->course;
     $result = true;
     if (!delete_records('assignment_submissions', 'assignment', $assignment->id)) {
         $result = false;
     }
     if (!delete_records('assignment', 'id', $assignment->id)) {
         $result = false;
     }
     if (!delete_records('event', 'modulename', 'assignment', 'instance', $assignment->id)) {
         $result = false;
     }
     // delete file area with all attachments - ignore errors
     require_once $CFG->libdir . '/filelib.php';
     fulldelete($CFG->dataroot . '/' . $assignment->course . '/' . $CFG->moddata . '/assignment/' . $assignment->id);
     assignment_grade_item_delete($assignment);
     return $result;
 }

// restored copy of the module
$newcmid = null;
$tasks = $rc->get_plan()->get_tasks();
foreach ($tasks as $task) {
    if (is_subclass_of($task, 'restore_activity_task')) {
        if ($task->get_old_contextid() == $cmcontext->id) {
            $newcmid = $task->get_moduleid();
            break;
        }
    }
}
// if we know the cmid of the new course module, let us move it
// right below the original one. otherwise it will stay at the
// end of the section
if ($newcmid) {
    $newcm = get_coursemodule_from_id('', $newcmid, $course->id, true, MUST_EXIST);
    moveto_module($newcm, $section, $cm);
    moveto_module($cm, $section, $newcm);
}
$rc->destroy();
if (empty($CFG->keeptempdirectoriesonbackup)) {
    fulldelete($backupbasepath);
}
echo $output->header();
if ($newcmid) {
    echo $output->confirm(get_string('duplicatesuccess', 'core', $a), new single_button(new moodle_url('/course/modedit.php', array('update' => $newcmid, 'sr' => $sectionreturn)), get_string('duplicatecontedit'), 'get'), new single_button(course_get_url($course, $cm->sectionnum, array('sr' => $sectionreturn)), get_string('duplicatecontcourse'), 'get'));
} else {
    echo $output->notification(get_string('duplicatesuccess', 'core', $a), 'notifysuccess');
    echo $output->continue_button(course_get_url($course, $cm->sectionnum, array('sr' => $sectionreturn)));
}
echo $output->footer();

         echo "<form action=\"coursefiles.php\" method=\"get\">\n";
         echo " <input type=\"hidden\" name=\"id\" value=\"{$id}\" />\n";
         echo " <input type=\"hidden\" name=\"wdir\" value=\"{$wdir}\" />\n";
         echo " <input type=\"hidden\" name=\"action\" value=\"cancel\" />\n";
         echo " <input type=\"submit\" value=\"{$strcancel}\" />\n";
         echo "</form>\n";
         echo "</td>\n</tr>\n</table>\n";
     }
     html_footer();
     break;
 case "delete":
     if ($confirm and confirm_sesskey()) {
         html_header($course, $wdir);
         foreach ($USER->filelist as $file) {
             $fullfile = $basedir . $file;
             if (!fulldelete($fullfile)) {
                 echo "<br />Error: Could not delete: {$fullfile}";
             }
         }
         clearfilelist();
         displaydir($wdir);
         html_footer();
     } else {
         html_header($course, $wdir);
         if (setfilelist($_POST)) {
             echo "<p align=center>" . get_string("deletecheckwarning") . ":</p>";
             print_simple_box_start("center");
             printfilelist($USER->filelist);
             print_simple_box_end();
             echo "<br />";
             $frameold = $CFG->framename;

 public function cleanup() {
     return fulldelete($this->directory);
 }

 /**
  * Processes this restore stage
  * @return bool
  * @throws restore_ui_exception
  */
 public function process()
 {
     global $CFG;
     if ($this->filename) {
         $archivepath = $CFG->tempdir . '/backup/' . $this->filename;
         if (!file_exists($archivepath)) {
             throw new restore_ui_exception('invalidrestorefile');
         }
         $outcome = $this->extract_file_to_dir($archivepath);
         if ($outcome) {
             fulldelete($archivepath);
         }
     } else {
         $fs = get_file_storage();
         $storedfile = $fs->get_file_by_hash($this->pathnamehash);
         if (!$storedfile || $storedfile->get_contenthash() !== $this->contenthash) {
             throw new restore_ui_exception('invalidrestorefile');
         }
         $outcome = $this->extract_file_to_dir($storedfile);
     }
     return $outcome;
 }

/**
 * Invalidate all server and client side JS caches.
 * @return void
 */
function js_reset_all_caches()
{
    global $CFG;
    require_once "{$CFG->libdir}/filelib.php";
    set_config('jsrev', empty($CFG->jsrev) ? 1 : $CFG->jsrev + 1);
    fulldelete("{$CFG->dataroot}/cache/js");
}

 /**
  * This function takes the combined pdf and embeds all the comments and annotations.
  * @param int|\assign $assignment
  * @param int $userid
  * @param int $attemptnumber (-1 means latest attempt)
  * @return stored_file
  */
 public static function generate_feedback_document($assignment, $userid, $attemptnumber)
 {
     $assignment = self::get_assignment_from_param($assignment);
     if (!$assignment->can_view_submission($userid)) {
         \print_error('nopermission');
     }
     if (!$assignment->can_grade()) {
         \print_error('nopermission');
     }
     // Need to generate the page images - first get a combined pdf.
     $file = self::get_combined_pdf_for_attempt($assignment, $userid, $attemptnumber);
     if (!$file) {
         throw new \moodle_exception('Could not generate combined pdf.');
     }
     $tmpdir = \make_temp_directory('assignfeedback_editpdf/final/' . self::hash($assignment, $userid, $attemptnumber));
     $combined = $tmpdir . '/' . self::COMBINED_PDF_FILENAME;
     $file->copy_content_to($combined);
     // Copy the file.
     $pdf = new pdf();
     $fs = \get_file_storage();
     $stamptmpdir = \make_temp_directory('assignfeedback_editpdf/stamps/' . self::hash($assignment, $userid, $attemptnumber));
     $grade = $assignment->get_user_grade($userid, true, $attemptnumber);
     // Copy any new stamps to this instance.
     if ($files = $fs->get_area_files($assignment->get_context()->id, 'assignfeedback_editpdf', 'stamps', $grade->id, "filename", false)) {
         foreach ($files as $file) {
             $filename = $stamptmpdir . '/' . $file->get_filename();
             $file->copy_content_to($filename);
             // Copy the file.
         }
     }
     $pagecount = $pdf->set_pdf($combined);
     $grade = $assignment->get_user_grade($userid, true, $attemptnumber);
     page_editor::release_drafts($grade->id);
     for ($i = 0; $i < $pagecount; $i++) {
         $pdf->copy_page();
         $comments = page_editor::get_comments($grade->id, $i, false);
         $annotations = page_editor::get_annotations($grade->id, $i, false);
         foreach ($comments as $comment) {
             $pdf->add_comment($comment->rawtext, $comment->x, $comment->y, $comment->width, $comment->colour);
         }
         foreach ($annotations as $annotation) {
             $pdf->add_annotation($annotation->x, $annotation->y, $annotation->endx, $annotation->endy, $annotation->colour, $annotation->type, $annotation->path, $stamptmpdir);
         }
     }
     fulldelete($stamptmpdir);
     $filename = self::get_downloadable_feedback_filename($assignment, $userid, $attemptnumber);
     $filename = clean_param($filename, PARAM_FILE);
     $generatedpdf = $tmpdir . '/' . $filename;
     $pdf->save_pdf($generatedpdf);
     $record = new \stdClass();
     $record->contextid = $assignment->get_context()->id;
     $record->component = 'assignfeedback_editpdf';
     $record->filearea = self::FINAL_PDF_FILEAREA;
     $record->itemid = $grade->id;
     $record->filepath = '/';
     $record->filename = $filename;
     // Only keep one current version of the generated pdf.
     $fs->delete_area_files($record->contextid, $record->component, $record->filearea, $record->itemid);
     $file = $fs->create_file_from_pathname($record, $generatedpdf);
     // Cleanup.
     @unlink($generatedpdf);
     @unlink($combined);
     @rmdir($tmpdir);
     return $file;
 }

//.........这里部分代码省略.........
    foreach ($cleanuplugintypes as $type) {
        if (!empty($callbacks[$type])) {
            foreach ($callbacks[$type] as $pluginfunction) {
                debugging("Callback delete_course is deprecated. Function {$pluginfunction} should be converted " . 'to observer of event \\core\\event\\course_content_deleted', DEBUG_DEVELOPER);
                $pluginfunction($course->id, $showfeedback);
            }
            if ($showfeedback) {
                echo $OUTPUT->notification($strdeleted . get_string('type_' . $type . '_plural', 'plugin'), 'notifysuccess');
            }
        }
    }
    // Delete questions and question categories.
    question_delete_course($course, $showfeedback);
    if ($showfeedback) {
        echo $OUTPUT->notification($strdeleted . get_string('questions', 'question'), 'notifysuccess');
    }
    // Make sure there are no subcontexts left - all valid blocks and modules should be already gone.
    $childcontexts = $coursecontext->get_child_contexts();
    // Returns all subcontexts since 2.2.
    foreach ($childcontexts as $childcontext) {
        $childcontext->delete();
    }
    unset($childcontexts);
    // Remove all roles and enrolments by default.
    if (empty($options['keep_roles_and_enrolments'])) {
        // This hack is used in restore when deleting contents of existing course.
        role_unassign_all(array('contextid' => $coursecontext->id, 'component' => ''), true);
        enrol_course_delete($course);
        if ($showfeedback) {
            echo $OUTPUT->notification($strdeleted . get_string('type_enrol_plural', 'plugin'), 'notifysuccess');
        }
    }
    // Delete any groups, removing members and grouping/course links first.
    if (empty($options['keep_groups_and_groupings'])) {
        groups_delete_groupings($course->id, $showfeedback);
        groups_delete_groups($course->id, $showfeedback);
    }
    // Filters be gone!
    filter_delete_all_for_context($coursecontext->id);
    // Notes, you shall not pass!
    note_delete_all($course->id);
    // Die comments!
    comment::delete_comments($coursecontext->id);
    // Ratings are history too.
    $delopt = new stdclass();
    $delopt->contextid = $coursecontext->id;
    $rm = new rating_manager();
    $rm->delete_ratings($delopt);
    // Delete course tags.
    core_tag_tag::remove_all_item_tags('core', 'course', $course->id);
    // Notify the competency subsystem.
    \core_competency\api::hook_course_deleted($course);
    // Delete calendar events.
    $DB->delete_records('event', array('courseid' => $course->id));
    $fs->delete_area_files($coursecontext->id, 'calendar');
    // Delete all related records in other core tables that may have a courseid
    // This array stores the tables that need to be cleared, as
    // table_name => column_name that contains the course id.
    $tablestoclear = array('backup_courses' => 'courseid', 'user_lastaccess' => 'courseid');
    foreach ($tablestoclear as $table => $col) {
        $DB->delete_records($table, array($col => $course->id));
    }
    // Delete all course backup files.
    $fs->delete_area_files($coursecontext->id, 'backup');
    // Cleanup course record - remove links to deleted stuff.
    $oldcourse = new stdClass();
    $oldcourse->id = $course->id;
    $oldcourse->summary = '';
    $oldcourse->cacherev = 0;
    $oldcourse->legacyfiles = 0;
    if (!empty($options['keep_groups_and_groupings'])) {
        $oldcourse->defaultgroupingid = 0;
    }
    $DB->update_record('course', $oldcourse);
    // Delete course sections.
    $DB->delete_records('course_sections', array('course' => $course->id));
    // Delete legacy, section and any other course files.
    $fs->delete_area_files($coursecontext->id, 'course');
    // Files from summary and section.
    // Delete all remaining stuff linked to context such as files, comments, ratings, etc.
    if (empty($options['keep_roles_and_enrolments']) and empty($options['keep_groups_and_groupings'])) {
        // Easy, do not delete the context itself...
        $coursecontext->delete_content();
    } else {
        // Hack alert!!!!
        // We can not drop all context stuff because it would bork enrolments and roles,
        // there might be also files used by enrol plugins...
    }
    // Delete legacy files - just in case some files are still left there after conversion to new file api,
    // also some non-standard unsupported plugins may try to store something there.
    fulldelete($CFG->dataroot . '/' . $course->id);
    // Delete from cache to reduce the cache size especially makes sense in case of bulk course deletion.
    $cachemodinfo = cache::make('core', 'coursemodinfo');
    $cachemodinfo->delete($courseid);
    // Trigger a course content deleted event.
    $event = \core\event\course_content_deleted::create(array('objectid' => $course->id, 'context' => $coursecontext, 'other' => array('shortname' => $course->shortname, 'fullname' => $course->fullname, 'options' => $options)));
    $event->add_record_snapshot('course', $course);
    $event->trigger();
    return true;
}

 /**
  * Return content of all files containing questions,
  * as an array one element for each file found,
  * For each file, the corresponding element is an array of lines.
  * @param string filename name of file
  * @return mixed contents array or false on failure
  */
 public function readdata($filename)
 {
     // Find if we are importing a .txt file.
     if (strtolower(pathinfo($filename, PATHINFO_EXTENSION)) == 'txt') {
         if (!is_readable($filename)) {
             $this->error(get_string('filenotreadable', 'error'));
             return false;
         }
         return file($filename);
     }
     // We are importing a zip file.
     // Create name for temporary directory.
     $uniquecode = time();
     $this->tempdir = make_temp_directory('webct_import/' . $uniquecode);
     if (is_readable($filename)) {
         if (!copy($filename, $this->tempdir . '/webct.zip')) {
             $this->error(get_string('cannotcopybackup', 'question'));
             fulldelete($this->tempdir);
             return false;
         }
         if (unzip_file($this->tempdir . '/webct.zip', '', false)) {
             $dir = $this->tempdir;
             if (($handle = opendir($dir)) == false) {
                 // The directory could not be opened.
                 fulldelete($this->tempdir);
                 return false;
             }
             // Create arrays to store files and directories.
             $dirfiles = array();
             $dirsubdirs = array();
             $slash = '/';
             // Loop through all directory entries, and construct two temporary arrays containing files and sub directories.
             while (false !== ($entry = readdir($handle))) {
                 if (is_dir($dir . $slash . $entry) && $entry != '..' && $entry != '.') {
                     $dirsubdirs[] = $dir . $slash . $entry;
                 } else {
                     if ($entry != '..' && $entry != '.') {
                         $dirfiles[] = $dir . $slash . $entry;
                     }
                 }
             }
             if (($handle = opendir($dirsubdirs[0])) == false) {
                 // The directory could not be opened.
                 fulldelete($this->tempdir);
                 return false;
             }
             while (false !== ($entry = readdir($handle))) {
                 if (is_dir($dirsubdirs[0] . $slash . $entry) && $entry != '..' && $entry != '.') {
                     $dirsubdirs[] = $dirsubdirs[0] . $slash . $entry;
                 } else {
                     if ($entry != '..' && $entry != '.') {
                         $dirfiles[] = $dirsubdirs[0] . $slash . $entry;
                     }
                 }
             }
             return file($dirfiles[1]);
         } else {
             $this->error(get_string('cannotunzip', 'question'));
             fulldelete($this->temp_dir);
         }
     } else {
         $this->error(get_string('cannotreaduploadfile', 'error'));
         fulldelete($this->tempdir);
     }
     return false;
 }

 /**
  * Cleans up stuff after the execution
  *
  * Note that we do not know if the execution was successful or not.
  * An exception might have been thrown.
  */
 protected function destroy()
 {
     global $CFG;
     if (empty($CFG->keeptempdirectoriesonbackup)) {
         fulldelete($this->get_workdir_path());
     }
 }

//.........这里部分代码省略.........
                            if ($userpref->value > 14 and $userpref->value < 21) {
                                $newvalue = 21;
                            } else {
                                if ($userpref->value > 7 and $userpref->value < 14) {
                                    $newvalue = 14;
                                } else {
                                    $newvalue = $userpref->value;
                                }
                            }
                        }
                    }
                }
            }
            $DB->set_field('user_preferences', 'value', $newvalue, array('id' => $userpref->id));
            // Update progress.
            $i++;
            $pbar->update($i, $total, "Upgrading user preference settings - {$i}/{$total}.");
        }
        $rs->close();
        $transaction->allow_commit();
        upgrade_main_savepoint(true, 2016011901.0);
    }
    if ($oldversion < 2016020200.0) {
        // Define field isstandard to be added to tag.
        $table = new xmldb_table('tag');
        $field = new xmldb_field('isstandard', XMLDB_TYPE_INTEGER, '1', null, XMLDB_NOTNULL, null, '0', 'rawname');
        // Conditionally launch add field isstandard.
        if (!$dbman->field_exists($table, $field)) {
            $dbman->add_field($table, $field);
        }
        // Define index tagcolltype (not unique) to be dropped form tag.
        $index = new xmldb_index('tagcolltype', XMLDB_INDEX_NOTUNIQUE, array('tagcollid', 'tagtype'));
        // Conditionally launch drop index tagcolltype.
        if ($dbman->index_exists($table, $index)) {
            $dbman->drop_index($table, $index);
        }
        // Define index tagcolltype (not unique) to be added to tag.
        $index = new xmldb_index('tagcolltype', XMLDB_INDEX_NOTUNIQUE, array('tagcollid', 'isstandard'));
        // Conditionally launch add index tagcolltype.
        if (!$dbman->index_exists($table, $index)) {
            $dbman->add_index($table, $index);
        }
        // Define field tagtype to be dropped from tag.
        $field = new xmldb_field('tagtype');
        // Conditionally launch drop field tagtype and update isstandard.
        if ($dbman->field_exists($table, $field)) {
            $DB->execute("UPDATE {tag} SET isstandard=(CASE WHEN (tagtype = ?) THEN 1 ELSE 0 END)", array('official'));
            $dbman->drop_field($table, $field);
        }
        // Main savepoint reached.
        upgrade_main_savepoint(true, 2016020200.0);
    }
    if ($oldversion < 2016020201.0) {
        // Define field showstandard to be added to tag_area.
        $table = new xmldb_table('tag_area');
        $field = new xmldb_field('showstandard', XMLDB_TYPE_INTEGER, '1', null, XMLDB_NOTNULL, null, '0', 'callbackfile');
        // Conditionally launch add field showstandard.
        if (!$dbman->field_exists($table, $field)) {
            $dbman->add_field($table, $field);
        }
        // By default set user area to hide standard tags. 2 = core_tag_tag::HIDE_STANDARD (can not use constant here).
        $DB->execute("UPDATE {tag_area} SET showstandard = ? WHERE itemtype = ? AND component = ?", array(2, 'user', 'core'));
        // Changing precision of field enabled on table tag_area to (1).
        $table = new xmldb_table('tag_area');
        $field = new xmldb_field('enabled', XMLDB_TYPE_INTEGER, '1', null, XMLDB_NOTNULL, null, '1', 'itemtype');
        // Launch change of precision for field enabled.
        $dbman->change_field_precision($table, $field);
        // Main savepoint reached.
        upgrade_main_savepoint(true, 2016020201.0);
    }
    if ($oldversion < 2016021500.0) {
        $root = $CFG->tempdir . '/download';
        if (is_dir($root)) {
            // Fetch each repository type - include all repos, not just enabled.
            $repositories = $DB->get_records('repository', array(), '', 'type');
            foreach ($repositories as $id => $repository) {
                $directory = $root . '/repository_' . $repository->type;
                if (is_dir($directory)) {
                    fulldelete($directory);
                }
            }
        }
        // Main savepoint reached.
        upgrade_main_savepoint(true, 2016021500.0);
    }
    if ($oldversion < 2016021501.0) {
        // This could take a long time. Unfortunately, no way to know how long, and no way to do progress, so setting for 1 hour.
        upgrade_set_timeout(3600);
        // Define index userid-itemid (not unique) to be added to grade_grades_history.
        $table = new xmldb_table('grade_grades_history');
        $index = new xmldb_index('userid-itemid-timemodified', XMLDB_INDEX_NOTUNIQUE, array('userid', 'itemid', 'timemodified'));
        // Conditionally launch add index userid-itemid.
        if (!$dbman->index_exists($table, $index)) {
            $dbman->add_index($table, $index);
        }
        // Main savepoint reached.
        upgrade_main_savepoint(true, 2016021501.0);
    }
    return true;
}