Information shows that in version 7.1, DateTime::__construct() can already support milliseconds. And specifically emphasize:

This means that naive comparisons of two newly created instances will now more likely return FALSE instead of TRUE: new DateTime() == new DateTime()

However, in my code, the millisecond part is always "000000", what is the problem:

format('u') != '000000') { file_put_contents('./msec.log', "$i:\t" . $date->format('s.u') . PHP_EOL, FILE_APPEND); // } }

Output:

0: 51.000000 1: 51.000000 2: 51.000000 …… 4999: 51.000000 5000: 51.000000 5001: 51.000000 …… 9997: 51.000000 9998: 51.000000 9999: 51.000000