JDK1.7.0_45文档中对System.currentTimeMills()的描述：
Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.
Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.
See the description of the class Date for a discussion of slight discrepancies that may arise between "computer time" and coordinated universal time (UTC).
- Returns:
- the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
可见这个方法获取的是当前系统时间与1970.1.1 0:0:0的时间差的毫秒数，最后一句提到这个时间是UTC的，所以在C#中应该如此实现：
long t = (long)(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1)).TotalMilliseconds);