Coroutine Countdown Timer being extremely slow - unity3d

Question

Hey guys so just as a disclaimer I'm relatively new to programming so if I'm making some super obvious mistake please go easy on me
So I'm trying to create a higher customizable Countdown timer for my game, and I want it to be able to be accurate to 0.01 Seconds. I decided I would use the Coroutine method for creating my timer instead of the delta-time one I have seen a couple of times, thinking that this would be a more efficient approach. My game is not very intensive and thus easily runs on hundreds of frames per second, so I thought that using Waitforseconds(0.01) is going to work better because it only needs to be called 100 times every second rather than multiple hundreds. however, I have come into a major issue with my timer. It is EXTREMELY slow. I ran the countdown timer on google and mine side by side starting at 25 seconds and it beat mine out by ten seconds. I even tried adding a artifical delay thinking the waitforseconds function was overshooting, so I would have the time tick down 0.01 seconds when a bit less then that had passed, but my results ended up being sort of inconsistent. Here is my code
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class TimerScript : MonoBehaviour
{
public Text textDisplay;
private double secondsLeft = 30;
public bool takingAway = false;
private string Texttodisplay;
public int Milisecondsdigits = 2;
void Start()
{
textDisplay = GetComponent<Text>();
Texttodisplay = "00:" + secondsLeft;
if(Milisecondsdigits == 0)
{
Milisecondsdigits = -1;
}
}
void Update()
{
if (takingAway == false && secondsLeft > 0)
{
StopAllCoroutines();
StartCoroutine(TimerTake());
}
if(Texttodisplay.Length > 8 - (Mathf.Abs(Milisecondsdigits -2)))
{
Texttodisplay = Texttodisplay.Substring(0,8- (Mathf.Abs(Milisecondsdigits -2)));
}
textDisplay.text = Texttodisplay;
}
IEnumerator TimerTake()
{
takingAway = true;
yield return new WaitForSeconds(0.01f);
secondsLeft -= 0.01;
if(secondsLeft < 10)
{
Texttodisplay = "00:0" + secondsLeft;
}
else
{
Texttodisplay = "00:" + secondsLeft;
}
takingAway = false;
}
}
could somebody please let me know how I could cause this to become more accurate or why it's acting extremely inaccurate currently :/

Answer 1

Coroutine events like WaitForSeconds trigger at a defined point in Unity's event cycle, which takes place after Update() is processed (see
https://docs.unity3d.com/Manual/ExecutionOrder.html). This defined execution point might not line up exactly with the timer delay. This means it may wait longer than you want it to.
In your example, you tell it to wait for 0.01 seconds. Let's say that you are running a game at 30 frames per second. The frame time for 30 frames per second is 1/30 seconds, or approximately 0.0333 seconds. WaitForSeconds will then wait for the next frame, and 0.0333 seconds passes until the next frame. Then the next WaitForSeconds event cycle, it sees that the delay has passed and triggers, but you actually waited over 3 times as long as you wanted to because of the delay between event cycles. Since your code assumes that WaitForSeconds had only waited for 0.01 seconds, you will end up waiting longer than you intended to. This normally doesn't matter in a lot of applications, but when accumulating with frequent short delays it certainly does.
To solve this, you have two choices:
Accumulate time manually using Time.deltaTime in Update().
Coroutines likely check their completion status per frame in a
similar way in the yield WaitForSeconds event. If coroutines
check if they need to continue every frame, doing this manually with
Time.deltaTime might not be any less efficient at all than a
coroutine. You will have to benchmark to find out, because coroutines being more efficient isn't a safe assumption.
Use Time.time (or Time.realtimeSinceStartup if you want it unscaled) to measure the actual span of time that elapsed after the WaitForSeconds trigger, and use that as what you subtract from your remaining time.
There is also an additional consideration here that if you want your
text display to update at specific regular intervals, you will want
to dynamically adjust what value you pass into WaitForSeconds to
compensate for its drift.

Answer 2

Do you try to do it without Corroutine in a fixed update? Fixed update refresh every 0.02 seconds by default but you can settup to run in 0.01 seconds in Edit > Settings > Time > Fixed Timestep.
Replace the corroutine with a function in FixedUpdate
There is a link with better explation how works fixedupdate.
FixedUpdate Unity