Is a timestamp in microseconds always unique?

Question

uniqid() in PHP generates a unique ID based on the current timestamp in microseconds. Is that really a foolproof way to generate a unique ID?

Even assuming there\'s

Answer 1

Ask yourself why you need uniqid in the first place. For instance, I use uniquid as the filename of uploads to my website. There can be any number of users who upload at the same time so what I am concerned with is two or more files having the same id, BUT I know that a single user can only upload one file at a time. So, I prepend the username in front and will always have uniqueness.

echo uniqid('username-'); // username-5621e3335ac0c

Of course, you should always ask yourself if you need to use uniquid in the first place. If you know the reason you are creating the id can only happen every x seconds, minutes, etc then you can create an id the same way just use time :

echo 'username-'.time(); // username-1445062025