[Python-Dev] Sporadic test failures in Lib/test/test_mimetools.py

[Tim Peters]

choose_boundary() ends likes so:

    timestamp = '%.3f' % time.time()
    seed = `random.randint(0, 32767)`
    return _prefix + '.' + timestamp + '.' + seed

On Windows, time.time() updates fewer than 100 times per second (but more
than 10), so the timestamp format is overly optimistic about how much unique
info it can get out of time.time().  The test in question calls
choose_boundary() 100 times as fast as it can, and on Windows probably no
more than two distinct time.time() values are seen for the duration.  The
chance of a boundary string duplicate is then about the chance of seeing a
duplicate from the randint() in 100 tries, which is non-trivial.

So there are more-or-less obvious flaws in this algorithm, but I don't think
there exist any simple methods to generate a guid that's truly gu.  Using a
threadsafe counter instead of randomization would at least be unique across
a program run.