My nginx server has crashed about 4 times over the past 2 days. MySQL, php-cgi, etc continues to run, just the nginx server itself crashes.

When I look in the nginx error logs, I see this line when it crashes:
sigtimedwait() failed (4: Interrupted system call)

Any ideas what this is? I tried searching Google and it came up with a couple foreign sites, so it doesn't seem to be a common issue.