Question

为什么DateTime.Subtract有时返回真正的奇数值？

private ConcurrentDictionary<string, Request> _waitingList = new ConcurrentDictionary<string, Request>();

// send requests in thread #1 and set their SentAt time
_waitingList.TryAdd(macAddress, request);
request.SentAt = DateTime.UtcNow;

// then in a timer tick event in different thread every 5 seconds
private void OnTimerTick(object sender, ElapsedEventArgs e) {
   foreach (var waiting in _waitingList) { // ConcurrentDictionary<string, Request>
      var request = waiting.Value;
      var msSinceSent = DateTime.UtcNow.Subtract(request.SentAt).TotalMilliseconds;
        Debug.WriteLine($"sent *{request.Type}* {msSinceSent} ms ago");
   }
}

sent *PackageUpdate* 336.2019 ms ago
sent *PackageUpdate* 698.1145 ms ago
sent *PackageUpdate* 1059.864 ms ago
sent *PackageUpdate* 63693095680615.5 ms ago

最后一个价值是巨大的，我经常得到这些价值，甚至不知道这怎么可能。

Answer 1

如果request.SentAt被设置为DateTime.MinValue，则将获得该值。我认为您的数据存储区中的值是null或零，并且正在某个地方转换为DateTime.MinValue。

例如，此代码：

Console.WriteLine(DateTime.UtcNow.Subtract(DateTime.MinValue).TotalMilliseconds);

将输出此值：

63693097183442.7

为什么有时DateTime.UtcNow.Subtract会给我大量的信息？

1 个答案: