Allow single user to edit Google Spreadsheet at a time - google-apps-script

Question

I have Google Spreadsheet say "A" that acts as a repository. Other users can read its content. I want to allow other users to run a script from a different spreadsheet to modify content of "A", but I want it to happen one by one so that changes from all users are recorded & not lost.
I tried doing it by having an additional sheet in "A" with its first cell value having current editor's user name & when current editor releases the sheet it sets value of first cell to blank. So that other users in queue can check if its available for edit. They can start editing it by setting first cell to their username. The problem is a waiting script at waiting editor's end is not able to capture a change in the value of first cell. So even if current editor releases "A", others are not able to start editing.
Please help.
Example:
SS - "A"
Its a data repository which contains data w.r.t. each user.
SS - "B"
This is distributed to all users. They can add their information in it & then press Save so that it gets added to "A". Now if two users click save together its possible that one user's updates are overwritten by second user.
I have this code in SS - "B"
It keeps checking for cell A1 in "Lock" sheet to be empty before proceeding with save command.
function savedata(){
var s1 = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
var wb = SpreadsheetApp.openById("XYZ");
var lck = wb.getSheetByName("Lock");
var uname = getUserEmail();
//Code stucks here, even if cell A1 in "Lock" sheet is set to blank if this loop has started it keeps on looping here. Logger continues to report old value of A1 cell.
while(lck.getRange(1,1).getValue()!=""){
Logger.log(lck.getRange(1,1).getValue(), lck.getRange(1,1).getValue());
}
lck.getRange(1,1).setValue(uname);
//Save data commands
lck.getRange(1,1).setValue("");
};

Answer 1

If all the users edit using the same script from the same sheet, you can use Lock service as mentioned here to prevent concurrent access to the code
Modify the code like so:
function savedata(){
var s1 = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Sheet1");
var wb = SpreadsheetApp.openById("XYZ");
var lck = wb.getSheetByName("Lock");
var uname = getUserEmail();
var lock = LockService.getScriptLock();
var success = lock.tryLock(10000); // Try getting lock for 10sec
if (!success) {
Logger.log("Currently Busy, Try again later")
return
} else {
Logger.log(lck.getRange(1,1).getValue(), lck.getRange(1,1).getValue());
}
lck.getRange(1,1).setValue(uname);
//Save data commands
lck.getRange(1,1).setValue("");
lock.releaseLock() //release lock so someone else can update.
};
This question explains how to use lock service in a concise format, if you would like to know.
Hope that helps!