Long Sleeps In Python

July 15, 2009 by Isaac

There is a portion of my test infrastructure that requires long sleep periods for stability soak testing purposes. So far the longest stability test run was 9 days. Originally, I simply used the time.sleep() method from the Python library. However, and I attribute this to VMware, I found that extremely inaccurate for long sleep durations. My test controller is running in a VM and although I have nothing to confirm this I suspect that VMware is doing funny stuff under the covers with the OS timer and that is throwing off the accuracy of time.sleep(). Anyway, here is my solution to the problem.

import time
from datetime import datetime, timedelta
 
def longsleep(minutes):
    """
    The normal time.sleep() method is not very accurate from inside
    VMware when sleeping for long periods of time.  This method is
    accurate to within +/- 5 seconds of the desired sleep time period.
    For long periods on the order of hours or days this small inaccuracy
    is acceptable.
    """
    sleepTimeSec = 60 * minutes
    now = datetime.utcnow()
    td = timedelta(seconds=sleepTimeSec)
    endTime = now + td
    while now <= endTime:
        time.sleep(5)
        now = datetime.utcnow()