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My users in App Script read their queue number from a Spreadsheet:

    var array = sessionsSheets.getRange(row, 2, 1, 3).getValues()[0];
    var questionNumber = array[2]; //This is the variable of interest, it is an integer signifying the queue
    sessionsSheets.getRange(`D${row}`).setFormula(questionNumber+1); //This is the updated queue

They then update this queue number as seen above. This method works fine most of the time, but if you take two devices and run the script simultaneously, they both receive the same queue, and the script will halt for one of them because you need a unique queue number later on to use Slides API:

    Slides.Presentations.batchUpdate({'requests': requests}, presentationId);

If promises worked, I would have simply put the Slides API line in a try block, and if an error of duplicity pops up, I would then call the same function recursively, up until overlap doesn't occur. However, promises are not supported in App Script, so what should I try instead?

OshiniRB
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Mike Harb
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    Although I'm not sure about your actual situation and the detailed script, is LockService used in your script? [Ref](https://developers.google.com/apps-script/reference/lock) If you have already used the LockService, I apologize. If you have never used the LockService, when you use it, is that the result you expect? – Tanaike Oct 10 '21 at 11:47
  • @Tanaike Very useful mechanism, the only problem is that I have users grouped into sessions. So if 1 user is accessing the script, I do not want to stop users from other sessions from editing their respective row in the document. I just want to stop users from his own session (identified by a token) – Mike Harb Oct 10 '21 at 13:08
  • Thank you for replying. I'm glad your issue was resolved. – Tanaike Oct 10 '21 at 23:01

1 Answers1

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I found a fix for my special case:

I used ScriptProperties in the Properties Services in App Script. When a user opens the application, he looks for the property of the key with his session's token. If it says busy, he waits and recursively tries the same function, if it says free, he changes it to busy, executes his APIs, then at the end changes it to free again.

Code Snippet:

function queueing(comment,name,token,sessionsSheets,row) {

var properties = PropertiesService.getScriptProperties();
var state = properties.getProperty(token);
if (state==null){
  properties.setProperty(token , `busy@0`);
  posting(comment,name,token,sessionsSheets,row,0);
} else if (state.includes("busy")){
  Logger.log('Gotta wait my turn');
  Utilities.sleep(2000);
  queueing(comment,name,token,sessionsSheets,row);
} else if (state.includes("free")){ 
  var questionNumber = state.split('@')[1];
  properties.setProperty(token , `busy@${questionNumber}`);
  posting(comment,name,token,sessionsSheets,row,questionNumber);
}}
Mike Harb
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