ids.py

#!/usr/bin/env python3

from time import sleep
from datetime import datetime, timezone

# Snowflake like ID generator that generates a 53-bit id suitable for sending as a number in JSON.

TIME_BITS    = 40
COUNTER_BITS = 10
MACHINE_BITS = 3

assert TIME_BITS + COUNTER_BITS + MACHINE_BITS <= 53

TIME_MASK    = (2 ** TIME_BITS) - 1
COUNTER_MASK = (2 ** COUNTER_BITS) - 1
MACHINE_MASK = (2 ** MACHINE_BITS) - 1

EPOCH = int(datetime(2016, 11, 8, tzinfo=timezone.utc).timestamp() * 1000)

def since_epoch():
    dt = datetime.utcnow()
    return int(dt.replace(tzinfo=timezone.utc).timestamp() * 1000) - EPOCH

def make_id(time, counter, machine_id):
    assert 0 <= machine_id <= 7, "Invalid machine id: {}".format(machine_id)
    t = (time & TIME_MASK) << (COUNTER_BITS + MACHINE_BITS)
    c = (counter & COUNTER_MASK) << MACHINE_BITS
    return t + c + machine_id

def ids(machine_id):
    counter = 0
    last_ts = 0
    while True:
        ts = since_epoch()
        # Whenever the counter rolls over wait a bit to make sure the
        # timestamp has advanced at least a millisecond.
        if counter == 0:
            while ts == last_ts:
                sleep(0.0001)
                ts = since_epoch()
            last_ts = ts
        yield make_id(ts, counter, machine_id)
        counter += 1
        counter %= (2 ** COUNTER_BITS)

def age(id):
    return id >> (COUNTER_BITS + MACHINE_BITS)

def counter(id):
    return (id >> MACHINE_BITS) & COUNTER_MASK

def machine(id):
    return id & MACHINE_MASK

if __name__ == '__main__':

    g1 = ids(0)
    for _ in range(1030):
        id = next(g1)
        print("{}: age: {}; counter: {}; machine: {}".format(id, age(id), counter(id), machine(id)))