Wait if code execution finished before a time limit and abort if didn't finish within limit

Question

I have for loop and I need each iteration to take exactly 5 milliseconds. ie if the code finishes before the 5 milliseconds the iteration should wait until the 5 milliseconds pass, and if it takes more than 5 milliseconds the loop should ignore it and go to next iteration.

I tried this code but it is not accurate and it doesn't help to abort to next iteration if it takes more time

import time

for i in range(N):
    now = time.time_ns()
    do_something(i)
    time.sleep(0.005 - (time.time_ns() - now -3)*1e-9)

I used time_ns() as I assumed it would be more accurate than time() but it didn't help much

Answer 1

Save init time at the beginning

and use in your computations. Here's my example

import random
import time

N = 10
D = 0.5
T0 = time.time()

def do_something(msg):
    """Sleep 0 to 1 seconds"""
    time.sleep(random.random())
    print(msg)

for i in range(N):
    # check if we're overtime
    if T0 + (i+1)*D < time.time():
        continue

    do_something(i)

    # use modulo to compute sleep duration
    time.sleep(
        D - (time.time() - T0) % D
    )

And the output. Notice some numbers are missing and that it takes 10×0.5 = 5 seconds.

$ time python3 aly.py 
0
1
3
5
6
8

real    0m5.030s
user    0m0.028s
sys     0m0.004s

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About time_ns : time.sleep needs float , so using integer nanoseconds is meaningless.