Windows Phone Emulator Time Skew When Computer Sleeps

I was working on my fork of an OAuth library for Windows Phone this weekend, and I ran across a really weird issue. I’m posting this in case someone else Googles this problem, since I couldn’t find anything.

I have a UNIX epoch timestamp generator (necessary for Twitter) class that looks like this:

    public class TimestampGenerator
    {
        public string Generate()
        {
            var unixEpoch = new DateTime(1970, 1, 1, 0, 0, 0);
            var now = DateTime.UtcNow;

            long stamp = ((now.Ticks - unixEpoch.Ticks) / 10000000);

            return stamp.ToString();
        }
    }

I worked for hours on this on my desktop and everything was working fine. Then, when I did a git pull on my laptop, it was suddenly broken. When I’d make a request to the term.ie example OAuth service, it said my timestamp was expired every time. I set breakpoints and compared it to the current epoch timestamp, and it was definitely wrong. I tried many ways of calculating it (that division is to get to seconds from 100 microsecond increments (ticks); I haven’t benchmarked to see which is faster), but nothing made a difference.

I calculated a time difference of about 102 hours from my current time based on the timestamps. I finally figured out that my emulator could have the wrong time, since I was thinking computer time == emulator time. I killed the emulator, hit F5, and it worked like a charm. Then, I thought about the time difference, and it was about the last time I put my laptop to sleep by closing its lid.

Apparently, when the computer comes out of sleep, the computer clock stops matching the emulator clock; the emulator clock freezes when the computer sleeps and just resumes from where it left off. I’m not sure if this is a bug or not, or if it happens on a regular basis. I may try to reproduce it later, but probably not.