Question

是否有其他人看过这个或知道如何关闭它？

我有代码定期检查BinaryWriter中流的位置。每次调用BinaryWriter.BaseStream.Position方法都会导致调用该流的Flush方法。

我尝试使用BinaryWriter和StreamWriter，只有BinaryWriter证明了这种行为。

以下示例代码：

namespace FlushaholicStreams
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var stream = new PrivateStream())
            using (var writer = new BinaryWriter(stream))
            {
                var data = "hi there, this is a really long string. Very very very long";

                for (int i = 0; i < 19; i++)
                {
                    data += data;
                }

                for (int j = 0; j < 8; j++)
                {
                    var bytes = Encoding.ASCII.GetBytes(data);
                    writer.Write(bytes);
                    var position = writer.BaseStream.Position;
                    Console.WriteLine("The position was {0}", position);
                }
            }

            Console.WriteLine("All done");
        }
    }

    class PrivateStream : MemoryStream
    {
        public int FlushCount = 0;
        public int CloseCount = 0;

        public override void Close()
        {
            this.CloseCount++;
            Console.WriteLine("Closing the stream");
            base.Close();
        }

        public override void Flush()
        {
            this.FlushCount++;
            Console.WriteLine("Flushing the stream");
            base.Flush();
        }
    }
}

该代码产生输出：

Flushing the stream
The position was 30932992
Flushing the stream
The position was 61865984
Flushing the stream
The position was 92798976
Flushing the stream
The position was 123731968
Flushing the stream
The position was 154664960
Flushing the stream
The position was 185597952
Flushing the stream
The position was 216530944
Flushing the stream
The position was 247463936
Flushed the stream 8 times
Closing the stream
Closing the stream
All done

我正在使用.Net 4.5

Answer 1

看起来BinaryWriter类强制过度刷新，并且无法覆盖它。我将保留对原始流的引用并直接检查它的位置。

我在这里找到了（涉嫌）源代码：

http://reflector.webtropy.com/default.aspx/4@0/4@0/DEVDIV_TFS/Dev10/Releases/RTMRel/ndp/clr/src/BCL/System/IO/BinaryWriter@cs/1305376/BinaryWriter@cs

/* 
* Returns the stream associate with the writer. It flushes all pending
* writes before returning. All subclasses should override Flush to 
* ensure that all buffered data is sent to the stream.
*/
public virtual Stream BaseStream {
  get { 
    Flush();
    return OutStream; 
  } 
}

// Clears all buffers for this writer and causes any buffered data to be
// written to the underlying device.
public virtual void Flush()
{ 
  OutStream.Flush();
}

Answer 2

框架容易出现冲动，是的。这很糟糕，因为它会强制磁盘访问。（主观注意：这是一个设计缺陷。）

给自己写一个包裹另一个流的Stream。在您的包装器类中，您将覆盖必要的方法以在实例字段中维护Position。这样，根本不需要访问包装流的Position成员。

.Net BinaryWriter在检查流位置时自动刷新流

2 个答案: