49.7 days

My Chromecast had been difficult to reach from my Pixel for a little more than a month, and then today it stopped showing up altogether. I tried my iPad and found it was unreachable from there too.

I factory reset the Chromecast. I was able to set it up, but not to use it, and the Google Home app told me to check my WiFi router.

I found it had been running for 83 days and counting. This is a short time in human terms; February 25 wasn’t that long ago. But it’s longer than vendors or developers leave WiFi routers running before rebooting them.

And, specifically, 83 days is longer than 49.7 days.

49.7 days is a magic number: it’s a uint32 of milliseconds. In other words, if you count up once a millisecond, you’ll overflow a 32-bit binary number in 49.7 days. And then weird things happen when time jumps backwards.

People have been writing variants of this bug for at least several decades, with no signs of stopping; I saw two more modern systems have problems at 49.7 days when I was working at Google Fiber.

It’s now my “all bets are off” uptime: the time where issues are likely to have knotty enough root causes they’re only worth fixing if someone is paying me to look. I rebooted my WiFi router, and my Chromecast started working again.