Why is the LockService is not working as intended? - google-apps-script

Question

I'm having a problem with the same entry begin saved multiple times and I realized it was mostly caused by double clicking. I'm trying to use LockService to avoid it: if the lock is not aquired in a millisecond the script should be aborted(because it's a duplicated operation).
//more code above
var lock = LockService.getScriptLock();
try{
lock.waitLock(1);//get the lock timing out in 1 millisecond
SpreadsheetApp.flush();
ss.insertRowBefore(6);
ss.getRange("A6").setValue(data[0][0]);
ss.getRange("B6").setValue(formatedString);
ss.getRange("C6").setValue(data[1][0]);
ss.getRange("D6").setValue(data[2][0]);
ss.getRange("E6").setValue(data[3][0]);
ss.getRange("F6").setValue(data[ref][0]);
SpreadsheetApp.flush();
Utilities.sleep(10);//This is to make sure it takes at least 1 millisecond
}
catch(e){
return;//It should generate a exception and end the script if the lock is not aquired
}
//more code bellow
The problem is that I still getting duplicated entries(tougth only 2 most of the time, so I believe it's working in part). What I am doing wrong?

Answer 1

Based on your sample sheet, you already read the data in the cells before you lock your succeeding code and clear its content.
Your original code:
var data = ss.getRange("B1:B2").getValues();
if(data[0][0] == "" || data[1][0] == "")
return;
var lock = LockService.getScriptLock();
try{
lock.waitLock(1);//get the lock timing out in 1 millisecond
SpreadsheetApp.flush();
ss.insertRowBefore(7);
ss.getRange("A7").setValue(data[0][0]);
ss.getRange("B7").setValue(data[1][0]);
SpreadsheetApp.flush();
Utilities.sleep(10);//This is to make sure it takes at least 1 millisecond
lock.releaseLock();
ss.getRange("B1:B2").setValue("");
}
catch(e){
return;//It should generate a exception and end the script if the lock is not aquired
}
What it does?
When you click submit button multiple times to execute your code, it will have n-times execution instance. As long as the clearing of cells don't take effect, each execution can write the data read from B1:B2.
Example:
Execution 1 started at 01:00:00.001 - already read the values in `B1:B2`
Execution 2 started at 01:00:00.005 - already read the values in `B1:B2`
Execution 3 started at 01:00:00.010 - already read the values in `B1:B2`
Execution 1 cleared B1:B2 content at 01:00:00.012. Hence you will have 3 copies of the submitted data. The writing of data in a new row was pended using the lock service, but the reading of data to add was not locked.
Solution
function submit() {
Utilities.sleep(1000);//simulate the upper part of the code
var ss = SpreadsheetApp.getActive().getSheetByName("spr1");
var lock = LockService.getScriptLock();
try{
lock.waitLock(1);//get the lock timing out in 1 millisecond
Logger.log("Locked: "+Utilities.formatDate(new Date(),Session.getScriptTimeZone(),"yyyy-MM-dd'T'HH:mm:ss.SSS"));
var data = ss.getRange("B1:B2").getValues();
Logger.log(data);
if(data[0][0] == "" || data[1][0] == "")
return;
SpreadsheetApp.flush();
ss.insertRowBefore(7);
ss.getRange("A7").setValue(data[0][0]);
ss.getRange("B7").setValue(data[1][0]);
Utilities.sleep(10);//This is to make sure it takes at least 1 millisecond
ss.getRange("B1:B2").setValue("");
SpreadsheetApp.flush();
lock.releaseLock();
Logger.log("UnLocked: "+Utilities.formatDate(new Date(),Session.getScriptTimeZone(),"yyyy-MM-dd'T'HH:mm:ss.SSS"));
}
catch(e){
return;//It should generate a exception and end the script if the lock is not acquired
}
Utilities.sleep(1000);//simulate the lower part of the code
}
Changes Done:
Lock the script first before reading the data in B1:B2
Make sure to clear the content of B1:B2 once it was added in a new row using flush() before releasing the lock.
Output:

Answer 2

Try this approach:
let lock = LockService.getScriptLock();
lock.tryLock(10000);
if (lock.hasLock()) {
ss.insertRowBefore(6);
ss.getRange(6, 1, 1, 6).setValues([data[0][0], formatedString, data[1][0], data[2][0]], data[3][0], data[ref][0])
SpreadsheetApp.flush();
lock.releaseLock();
}

Answer 3

I managed to solve my problem by adding a "flag" cell to count the numbers of active submissions. I'm using the lock only around it.
var rep = ss.getRange("C1");//the flag starting with 0
var lock = LockService.getScriptLock();
try{
lock.waitLock(1000);
var vAtual = rep.getValue();
if(vAtual >= 1)
return;//return hopefully if it already have one active submission
rep.setValue(vAtual+1);//increment for each active submit
SpreadsheetApp.flush();
lock.releaseLock();
}
catch(e){
return;
}
It's not pretty but it worked, so far. But I would still like to know why my original lock strategy failed. It can help some other people with similar problems too.