Running time exceeded (Help with Token Usage)

Question

I have looked through a number of the questions asked on this particular question however none of the solutions I have seen appear to apply to what I am working on.

I have a script which is attached to a spreadsheet, the goal is to run this script each night to generate a master file listing of all files in the drive and present them on a spreadsheet. Due to the number of files in folders, sub-folders, sub-sub-folders (you get the idea) it is unable to complete the update to the spreadsheet within the specified time frame.

function clear_spreadsheet() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  sheet.clear();
  sheet.appendRow(['Name', 'Folder','Link', 'Last Updated']);
 }

function listFolders(folder) {
folder = folder || DriveApp.getRootFolder();
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();

var file;
var name;
var urllink;
var row;
var currentfolder;
var lastupdated;
var files = folder.getFiles();

while ( files.hasNext() ) {
 file = files.next();
 name = file.getName();
 urllink = file.getUrl();
 currentfolder = file.getParents();
 lastupdated = file.getLastUpdated();
 sheet.appendRow( [name, folder, urllink, lastupdated]);
}

var subfolders = folder.getFolders();

while (subfolders.hasNext()) {
listFolders(subfolders.next());
}

};

function Run_Update(Folder) {
clear_spreadsheet();
listFolders();
}

Any thoughts as to how I can either streamline the code to run faster, or more likely find a way to generate a placeholder within the script and continue to run after a specified time frame until it comes to the end of its search?

EDIT: I've seen that you can utilize tokens and timers to facilitate this however its not something I am familiar with. Does anyone know the process for calling this type of function in this manner?

EDIT 2 See below for the final code which resolved the issue of exceeding the run time in this particular instance.

function Start_Up() {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = spreadsheet.getActiveSheet();
  sheet.clear();
  sheet.appendRow(['Name', 'Folder', 'URL', 'Updated'])

  var start_time = new Date();
    MailApp.sendEmail({
      to: 'add your email',
      subject: "Master File Update - Complete",
      htmlBody: "The update of the master equipment document spreadsheet was started at: " + start_time});

  var Script_Properties = PropertiesService.getScriptProperties();
  Script_Properties.deleteAllProperties();
  Iterate_Files();
}

function Delete_Triggers() {
  var Triggers = ScriptApp.getProjectTriggers();
  for (var i = 0; i < Triggers.length; i++) {
    ScriptApp.deleteTrigger(Triggers[i]);    
  }
}

function Iterate_Files() {
  var Script_Properties = PropertiesService.getScriptProperties();
  var continuationToken = Script_Properties.getProperty('C_Token');

  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = spreadsheet.getActiveSheet();

  Delete_Triggers();

  var Start_Time = new Date().getTime();
  var Seconds = 0; 

  if (continuationToken) {
    var files = DriveApp.continueFileIterator(continuationToken);
  } else {
    var files = DriveApp.getFiles();
  }

  var output = [];

  while (files.hasNext() && Seconds < 240) {
    var file = files.next();
    var Current_Time = new Date().getTime();
    var Seconds = Math.floor((Current_Time - Start_Time)/1000);

    var file_name = file.getName();
    if (file.getParents().hasNext()) {
      var folder_name = file.getParents().next().getName();
    } else {
      folder_name = 'Root';
    }
    var file_url = file.getUrl();
    var file_last_updated = file.getLastUpdated();
    output.push([file_name, folder_name , file_url, file_last_updated]);
  }
  if (output.length) {
    var last_row = sheet.getLastRow();
    sheet.getRange(last_row +1, 1, output.length, 4).setValues(output);
  }

  if (files.hasNext()) {
    var triggerID = null;
    continuationToken = files.getContinuationToken();
    Script_Properties.setProperty('C_Token', continuationToken);
    ScriptApp.newTrigger('Iterate_Files')
    .timeBased()
    .after(1 * 60 * 1000)
    .create();
  } else {
    Script_Properties.deleteAllProperties();
    var end_time = new Date();
    MailApp.sendEmail({
      to: 'add your email',
      subject: "Master File Update - Complete",
      htmlBody: "The update of the master equipment document spreadsheet was completed at: " + end_time});

    ScriptApp.newTrigger('Start_Up')
    .timeBased()
    .everyDays(1)
    .atHour(0)
    .create();
  }
}

Answer 1

You may be able to improve the performance by replacing individual row insertions in a loop by a batch operation post-loop (as Google themselves recommend):

var output = []; 
while (files.hasNext() ) {
 file = files.next();
 name = file.getName();
 urllink = file.getUrl();
 currentfolder = file.getParents();
 lastupdated = file.getLastUpdated();
 output.push([name, folder, urllink, lastupdated]);
}
if (output.length) {
  var lastRow = sheet.getRange.getLastRow();
  sheet.getRange(lastRow + 1, 1, output.length, 4).setValues(output);
}

Apart from that, you could try to split the task into smaller one: for example, "process the folders where the first character of the name is in the range A-E". Then set separate triggers for such functions, for different times. However, the algorithm gets a bit complicated since one should go through the subfolders under a folder that itself isn't a part of the currently processed range.

As a last resort, there's a way stop/resume the execution of a script, see this answer. You can try storing folder Id in script properties and resuming with that folder. But this also gets complicated because of the nested structure: there are file/folder iterators that you can't simply store and renew.