为什么SystemClock.UtcNow.Milliseconds总是0

Question

我将ISystemClock注入我的服务：

public class EventSink
{
    private readonly ISystemClock _systemClock;

    public EventSink(ISystemClock systemClock)
    {
        _systemClock = systemClock;
    }

    private async Task SaveEvent(CancellationToken ct)
    {
        var event = new MyEvent
        {
            Timestamp = _systemClock.UtcNow.DateTime
        };
    }
}

它只是在启动时注册：

services.AddScoped<ISystemClock, SystemClock>();

但是DateTime毫秒属性始终为0。

而且，这个new SystemClock().UtcNow.Millisecond总是返回0。

直接窗口的例子：

DateTime.UtcNow.Millisecond
786
new SystemClock().UtcNow.Millisecond
0
System.DateTimeOffset.UtcNow.Millisecond;
265

​

​

Answer 1

找到答案，这是SystemClock的源代码

        public DateTimeOffset UtcNow
    {
        get
        {
            // the clock measures whole seconds only, to have integral expires_in results, and
            // because milliseconds do not round-trip serialization formats
            var utcNowPrecisionSeconds = new DateTime((DateTime.UtcNow.Ticks / TimeSpan.TicksPerSecond) * TimeSpan.TicksPerSecond, DateTimeKind.Utc);
            return new DateTimeOffset(utcNowPrecisionSeconds);
        }
    }