.Net 提供了一個NetworkStream 用于TCP 的讀寫，實際使用時發(fā)現(xiàn)直接操作效率很低，哪怕把TCP 的發(fā)送緩存和接受緩存設(shè)置很大也沒有太大提高。后來在對 NetworkStream 讀寫前設(shè)置了緩存，性能一下子提高了很多。
從實際測試結(jié)果看設(shè)置自己的寫緩存，對性能的提升最為顯著。我分析了一下，其原因很可能是在向NetworkStream 序列化對象時，序列化程序調(diào)用了大量的Write 方法向NetworkStream寫入數(shù)據(jù)，每次向NetworkStream寫入數(shù)據(jù)，數(shù)據(jù)被首先寫入TCP的發(fā)送緩存，并且由調(diào)用線程設(shè)置一個信號通知.Net framework 內(nèi)部的TCP線程發(fā)送緩沖區(qū)中已經(jīng)有數(shù)據(jù)，TCP線程被激活并讀取發(fā)送緩沖區(qū)中的數(shù)據(jù)，組包并向網(wǎng)卡寫入數(shù)據(jù)。頻繁的調(diào)用 NetworkStream.Write 寫入小塊數(shù)據(jù)將導(dǎo)致調(diào)用線程和TCP線程反復(fù)切換，并大量觸發(fā)網(wǎng)卡中斷，導(dǎo)致發(fā)送效率低下。如果我們在發(fā)送前將數(shù)據(jù)緩存并按較大的數(shù)據(jù)塊發(fā)送給TCP線程，則大大減少線程切換和網(wǎng)卡中斷數(shù)量，從而大大提高傳輸效率。
問題到這里還沒有結(jié)束，我們發(fā)送的對象往往較大，如果我們將發(fā)送對象全部序列化到buffer中再發(fā)送，那么勢必占用大量內(nèi)存，實際上我們無法忍受這種對內(nèi)存無限制申請的行為，試想一個1G大小的對象，我們在發(fā)送前為它另外再開辟1個G的內(nèi)存來緩存，對于系統(tǒng)來說簡直是無法忍受。由于我們用.net 發(fā)送數(shù)據(jù),我們在發(fā)送時需要將對象序列化到流中，而不能像 C/C++那樣直接通過指針來讀取數(shù)據(jù)（當(dāng)然你也可以用unsafe代碼，但這種方式會帶來其他問題，而且并不為大家所推薦），所以我們需要開發(fā)一個專門用 TCP 發(fā)送緩存的流來處理讀寫前的緩存。為此我開發(fā)了一個 TcpCacheStream 類，這個類被用在讀寫 NetworkStream 前先進(jìn)行緩存。
調(diào)用方法很簡單
- 發(fā)送過程
object msg;//初始化 msg 過程省略System.Net.Sockets.NetworkStream _ClientStream;
//初始化 _ClientStream 過程省略//創(chuàng)建TcpCacheStream TcpCacheStream tcpStream = new TcpCacheStream(_ClientStream);//二進(jìn)制序列化 msg 對象到 TcpCacheStream IFormatter formatter = new BinaryFormatter();formatter.Serialize(tcpStream, msg);
//將緩存中最后一包的數(shù)據(jù)發(fā)送出去tcpStream.Flush();
- 接收過程
System.Net.Sockets.NetworkStream _ClientStream;
//初始化 _ClientStream 過程省略//創(chuàng)建TcpCacheStream TcpCacheStream tcpStream = new TcpCacheStream(_ClientStream);//從 TcpCacheStream 二進(jìn)制反序列化IFormatter formatter = new BinaryFormatter();objcet result = formatter.Deserialize(tcpStream);
TcpCacheStream 類為調(diào)用者封裝了緩存的過程，這個緩存過程實際并不復(fù)雜，發(fā)送時數(shù)據(jù)先寫入TcpCacheStream的buf中，當(dāng)buf滿后才向NetworkStream 寫入數(shù)據(jù)，否則只緩存。由于最后一包不能保證正好填滿buf，我們在寫入數(shù)據(jù)后一定要調(diào)用 Flush 方法，將所有數(shù)據(jù)都發(fā)送出去。接收的過程反過來，如果buf中沒有數(shù)據(jù)，就先將數(shù)據(jù)讀入到buf中，然后再COPY給調(diào)用者，如果已經(jīng)有數(shù)據(jù)則直接COPY給調(diào)用者。
TcpCacheStream 的代碼如下：
[Serializable]
public class TcpCacheStream : Stream
{ #region Private fieldsconst int BUF_SIZE = 4096;
private byte[] _Buf = new byte[BUF_SIZE];
private MemoryStream _CacheStream = new MemoryStream(BUF_SIZE);
private NetworkStream _NetworkStream;private int _BufLen = 0;
#endregion #region Private properties private MemoryStream CacheStream {get
{ return _CacheStream;}
}
#endregion #region Public properties /// <summary> /// get or set the Network Stream /// </summary> public NetworkStream NetworkStream {get
{ return _NetworkStream;}
}
#endregion public TcpCacheStream(NetworkStream networkStream) {_NetworkStream = networkStream;
}
#region Implement stream class
public override bool CanRead
{get
{return true;
}
}
public override bool CanSeek
{get
{return false;
}
}
public override bool CanWrite
{get
{return true;
}
}
public override void Flush()
{NetworkStream.Write(_Buf, 0, _BufLen);
NetworkStream.Flush();
}
public override long Length
{get
{throw new Exception("This stream can not seek!");
}
}
public override long Position
{get
{throw new Exception("This stream can not seek!");
}
set
{throw new Exception("This stream can not seek!");
}
}
public override int Read(byte[] buffer, int offset, int count)
{ int len = 0; //If cache is not empty, read from cache if (CacheStream.Length > CacheStream.Position) {len = CacheStream.Read(buffer, offset, count);
return len;}
//Fill cachelen = NetworkStream.Read(_Buf, 0, BUF_SIZE);
if (len == 0) { return 0;}
CacheStream.Position = 0;
CacheStream.Write(_Buf, 0, len);
CacheStream.SetLength(len);
CacheStream.Position = 0;
len = CacheStream.Read(buffer, offset, count);
return len;}
public override long Seek(long offset, SeekOrigin origin)
{throw new Exception("This stream can not seek!");
}
public override void SetLength(long value)
{throw new Exception("This stream can not seek!");
}
public override void Write(byte[] buffer, int offset, int count)
{ if (offset + count > buffer.Length) {throw new ArgumentException("Count + offset large then buffer.Length");
}
int remain = count - (BUF_SIZE - _BufLen); if (remain < 0) {Array.Copy(buffer, offset, _Buf, _BufLen, count);
_BufLen = BUF_SIZE + remain;
}
else {Array.Copy(buffer, offset, _Buf, _BufLen, BUF_SIZE - _BufLen);
NetworkStream.Write(_Buf, 0, _Buf.Length);
Array.Copy(buffer, offset + BUF_SIZE - _BufLen, _Buf, 0, remain);
_BufLen = remain;
}
}
#endregion}
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