在开发大量Socket并发服务器，完成端口加重叠I/O是迄今为止最好的一种解决方案，下面是简单的介绍：
   “完成端口”模型是迄今为止最为复杂的一种I/O模型，特别适合需要同时管理为数众多的套接字，采用这种模型，往往可以达到最佳的系统性能。但是只适合Windows NT和Windows 2000及以上操作系统。因其设计的复杂性，只有在你的应用程序需要同时管理数百乃至上千套接字的时候，而且希望随着系统内安装的CPU数量增多，应用程序的性能也可以线性提升，才考虑采用“完成端口”模型。
    重叠I/O（Overlapped I/O）模型使应用程序达到更佳的系统性能。重叠模型的基本设计原理便是让应用程序使用一个重叠的数据结构，一次投递一个或多个Winsock I/O请求。针对哪些提交的请求，在它们完成之后，应用程序可为它们提供服务。该模型适用于除Windows CE之外的各种Windows平台。
    开发完成端口最具有挑战是线程个数和管理内存，创建一个完成端口后，就需要创建一个或多个“工作者线程”，以便在I/O请求投递给完成端口对象后，为完成端口提供服务。但是到底应创建多少个线程，这实际正是完成端口最为复杂的一个方面，一般采用的是为每一个CPU分配一个线程（有的是CPU个数加1，有的是CPU*2的线程个数）。内存分配效率低是因为应用程序在分配内存的时候，系统内核需要不停的Lock/UnLock，而且在多CPU的情况下，会成为整个程序性能的瓶颈，不能随CPU的个数增加而性能提高，一种比较好的做法一个一次分配多块内存。
    下面是我写一个的完成端口的演示程序，在我的电脑上测试可以达到链接5100个客服端，服务器性能还很好，由于我写的客服端占用资源比较的，最后直接重启了，具体见代码。演示程序主要的瓶颈在于发消息的这一块，在实际应用中应去掉。

（配置：操作系统 Microsoft Windows XP Professional 操作系统 Service Pack 版本 Service Pack 2；CPU：Intel(R) Pentium(R)4 2.40GHz 2.40GHz；内存：2G；主板：华硕P4P800）。

主要源代码：(Delphi 7编写)，下载地址：http://download.csdn.net/source/818039

{*******************************************************}
{                                                       }
{       高性能服务器，这个是一个演示DEMO                }
{                                                       }
{       联系邮箱：[email protected]                   }
{                                                       }
{*******************************************************}

unit IOCPSvr;

interface

uses
 Windows, Messages, WinSock2, Classes, SysUtils, SyncObjs;

const
  {* 每一次发送和接收的数据缓冲池大小 *}
  MAX_BUFSIZE = 4096;
  {* 关闭客户端通知消息 *}
  WM_CLIENTSOCKET = WM_USER + $2000;

type
  {* Windows Socket 消息 *}
  TCMSocketMessage = packed record
    Msg: Cardinal;
    Socket: TSocket;
    SelectEvent: Word;
    SelectError: Word;
    Result: Longint;
  end;

  {* IOCP服务器运行轨迹 *}
  TSocketEvent = (seInitIOPort, seUninitIOPort, seInitThread, seUninitThread,
    seInitSocket, seUninitSocket, seConnect, seDisconnect, seListen, seAccept, seWrite, seRead);
const
  CSSocketEvent: array[TSocketEvent] of string = ('InitIOPort', 'UninitIOPort', 'InitThread', 'UninitThread',
    'InitSocket', 'UninitSocket', 'Connect', 'Disconnect', 'Listen', 'Accept', 'Write', 'Read');
type
  {* 产生错误类型 *}
  TErrorEvent = (eeGeneral, eeSend, eeReceive, eeConnect, eeDisconnect, eeAccept);

  {* 完成端口传递的结构体 *}
  TIOCPStruct = packed record
    Overlapped: OVERLAPPED;
    wsaBuffer: TWSABUF;
    Event: TSocketEvent; //读或写
    Buffer: array [0..MAX_BUFSIZE - 1] of Char;
    Assigned: Boolean;  //表示已经分配给某个客户端
    Active: Boolean;    //客服端内部使用，表示是否正在使用
  end;
  PIOCPStruct = ^TIOCPStruct;

  EMemoryBuffer = class(Exception);
  ESocketError = class(Exception);

  TMemoryManager = class;
  TServerSocket = class;
  TSymmetricalSocket = class;

  TMemoryManager = class
  private
    {* 管理内存使用 *}
    FList: TList;
    {* 分配和释放时候使用的锁 *}
    FLock: TCriticalSection;
    {* 服务器 *}
    FServerSocket: TServerSocket;
    function GetCount: Integer;
    function GetIOCPStruct(AIndex: Integer): PIOCPStruct;
  public
    constructor Create(AServerSocket: TServerSocket; ACount: Integer); overload;
    constructor Create(AServerSocket: TServerSocket); overload;
    destructor Destroy; override;

    {* 分配内存使用权 *}
    function Allocate: PIOCPStruct;
    {* 释放内存使用权 *}
    procedure Release(AValue: PIOCPStruct);
    property Server: TServerSocket read FServerSocket;
    property Count: Integer read GetCount;
    property Item[AIndex: Integer]: PIOCPStruct read GetIOCPStruct;
  end;

  {* 客服端链接服务器触发此事件，如果要拒绝链接，把AConnect := False *}
  TOnBeforeConnect = procedure(ASymmIP: string; AConnect: Boolean) of object;
  {* 链接完成之后触发此事件 *}
  TOnAfterConnect = procedure(ASymmetricalSocket: TSymmetricalSocket) of object;
  {* 断开连接触发事件 *}
  TOnAfterDisconnect = procedure(ASymmetricalSocket: TSymmetricalSocket) of object;
  {* 收到数据会触发此事件 *}
  TOnDataEvent = procedure(ASymmetricalSocket: TSymmetricalSocket; AData: Pointer;
    ACount: Integer) of object;
  {* 错误触发事件 *}
  TOnErrorEvent = procedure(AError: Integer; AErrorString: string; AInfo: string; var AHandleError: Boolean) of object;
  {* 服务器运行LOG *}
  TOnLog = procedure (ASocketEvent: TSocketEvent; AInfo: string) of object;

  {* 服务器，负责建立完成端口，管理内存和管理客服端，及Socket消息循环 *}
  TServerSocket = class
  private
    {* 内存管理 *}
    FMemory: TMemoryManager;
    {* 端口 *}
    FPort: Integer;
    {* 套接字 *}
    FSocket: TSocket;
    {* 完成端口句柄 *}
    FIOCPHandle: THandle;
    {* 消息循环句柄 *}
    FHandle: THandle;
    {* 对等的客服端 *}
    FClients: TList;
    {* 服务器运行线程 *}
    FThreads: TList;
    {* 监听线程 *}
    FAcceptThread: TThread;
    {* 表示是否激活 *}
    FActive: Boolean;
    {* 锁 *}
    FLock: TCriticalSection;
    {* 错误触发事件 *}
    FOnError: TOnErrorEvent;
    {* 书写LOG *}
    FOnLog: TOnLog;
    {* 接收连接事件 *}
    FOnBeforeConnect: TOnBeforeConnect;
    {* 连接成功之后的事件 *}
    FOnAfterConnect: TOnAfterConnect;
    {* 断开连接事件 *}
    FOnAfterDisconnect: TOnAfterDisconnect;
    {* 接收数据 *}
    FOnRead: TOnDataEvent;

    procedure WndProc(var AMsg: TMessage);
    {* 激活 *}
    procedure Open;
    {* 关闭 *}
    procedure Close;
    {* 设置激活/关闭 *}
    procedure SetActive(AValue: Boolean);
    {* 触发错误 *}
    function CheckError(AErrorCode: Integer = -1; AInfo: string = ''): Boolean;
    {* 触发LOG *}
    procedure DoLog(ASocketEvent: TSocketEvent; AInfo: string = '');
    {* 设置端口 *}
    procedure SetPort(AValue: Integer);
    {* 注册一个客服端，由于在另外一个线程中调用，需要加锁 *}
    procedure RegisterClient(ASocket: TSymmetricalSocket);
    {* 反注册一个客服端，由于在另外一个线程中调用，需要加锁 *}
    procedure UnRegisterClient(ASocket: TSymmetricalSocket);
    {* 通过Socket句柄查找对等的TSymmetricalSocket *}
    function FindSymmClient(ASocket: TSocket): TSymmetricalSocket;
    {* 客服端关闭消息 *}
    procedure WMClientClose(var AMsg: TCMSocketMessage); message WM_CLIENTSOCKET;
    {* 连接时触发的事件 *}
    function DoConnect(ASocket: TSocket): Boolean;
    {* 连接完成之后触发事件 *}
    procedure DoAfterConnect(ASymSocket: TSymmetricalSocket);
    {* 连接断开触发事件 *}
    procedure DoDisConnect(ASymSocket: TSymmetricalSocket);
    {* 接收数据触发的事件 *}
    procedure DoRead(ASymmetricalSocket: TSymmetricalSocket; AData: Pointer;
      ACount: Integer);
    {* 获得客服端个数 *}
    function GetClientCount: Integer;
    function GetClient(const AIndex: Integer): TSymmetricalSocket;
  public
    constructor Create;
    destructor Destroy; override;
    {* 接收一个客服端，被接收线程调用 *}
    procedure AcceptClient;

    property Port: Integer read FPort write SetPort;
    property Socket: TSocket read FSocket;
    property Handle: THandle read FHandle;
    property Active: Boolean read FActive write SetActive;
    property MemoryManager: TMemoryManager read FMemory;
    {* 事件 *}
    property OnError: TOnErrorEvent read FOnError write FOnError;
    property OnLog: TOnLog read FOnLog write FOnLog;
    property OnRead: TOnDataEvent read FOnRead write FOnRead;
    property OnBeforeConnect: TOnBeforeConnect read FOnBeforeConnect write FOnBeforeConnect;
    property OnAfterConnect: TOnAfterConnect read FOnAfterConnect write FOnAfterConnect;
    property OnAfterDisConnect: TOnAfterDisconnect read FOnAfterDisconnect write FOnAfterDisconnect;
    property ClientCount: Integer read GetClientCount;
    property Client[const AIndex: Integer]: TSymmetricalSocket read GetClient;
  end;

  {* 接收数据、发送数据及管理分配的内存 *}
  TSymmetricalSocket = class
  private
    FSocket: TSocket;
    FServer: TServerSocket;
    FAssignMemory: TList;
    FRemoteAddress, FRemoteHost: string;
    FRemotePort: Integer;

    {* 准备接收数据 *}
    function PrepareRecv(AIOCPStruct: PIOCPStruct = nil): Boolean;
    {* 获得完成端口内存块使用权 *}
    function Allocate: PIOCPStruct;
    {* 处理接收的数据 *}
    function WorkBlock(AIOCPStruct: PIOCPStruct; ACount: DWORD): Integer;
    {* 获得地方IP *}
    function GetRemoteIP: string;
    {* 获得远程机器名 *}
    function GetRemoteHost: string;
    {* 获得远程端口 *}
    function GetRemotePort: Integer;
  public
    constructor Create(ASvrSocket: TServerSocket; ASocket: TSocket);
    destructor Destroy; override;
    {* 发送数据 *}
    function Write(var ABuf; ACount: Integer): Integer;
    function WriteString(const AValue: string): Integer;

    property Socket: TSocket read FSocket;
    property RemoteAddress: string read GetRemoteIP;
    property RemoteHost: string read GetRemoteHost;
    property RemotePort: Integer read GetRemotePort;
  end;

  TSocketThread = class(TThread)
  private
    FServer: TServerSocket;
  public
    constructor Create(AServer: TServerSocket);
  end;

  TAcceptThread = class(TSocketThread)
  protected
    procedure Execute; override;
  end;

  TWorkThread = class(TSocketThread)
  protected
    procedure Execute; override;
  end;

implementation

uses
  RTLConsts;

const
 SHUTDOWN_FLAG = $FFFFFFFF;

{ TMemoryManager }

constructor TMemoryManager.Create(AServerSocket: TServerSocket;
  ACount: Integer);
var
  i: Integer;
  pIOCPData: PIOCPStruct;
begin
  inherited Create;
  FList := TList.Create;
  FLock := TCriticalSection.Create;
  for i := 1 to ACount do
  begin
    New(pIOCPData);
    FillChar(pIOCPData^, SizeOf(PIOCPStruct), 0);
    {* 下面两句其实由FillChar已经完成，在这写，只是为了强调 *}
    pIOCPData.Assigned := False;
    pIOCPData.Active := False;
    FList.Add(pIOCPData);
  end;
end;

function TMemoryManager.Allocate: PIOCPStruct;
var
  i: Integer;
begin
  FLock.Enter;
  try
    Result := nil;
    for i := 0 to FList.Count - 1 do
    begin
      Result := FList[i];
      if not Result.Assigned then
        Break;
    end;
    if (not Assigned(Result)) or (Result.Assigned) then
    begin
      New(Result);
      FList.Add(Result);
    end;
    FillChar(Result^, SizeOf(TIOCPStruct), 0);
    Result.Assigned := True;
    Result.Active := False;
  finally
    FLock.Leave;
  end;
end;

constructor TMemoryManager.Create(AServerSocket: TServerSocket);
begin
  Create(AServerSocket, 200);
end;

destructor TMemoryManager.Destroy;
var
  i: Integer;
begin
  for i := 0 to FList.Count - 1 do
    FreeMem(FList[i]);
  FList.Clear;
  FList.Free;
  FLock.Free;
  inherited;
end;

function TMemoryManager.GetCount: Integer;
begin
  Result := FList.Count;
end;

function TMemoryManager.GetIOCPStruct(AIndex: Integer): PIOCPStruct;
begin
  Result := nil;
  if (AIndex >= FList.Count) or (AIndex < 0) then
    EMemoryBuffer.CreateFmt(SListIndexError, [AIndex])
  else
    Result := FList[AIndex];
end;

procedure TMemoryManager.Release(AValue: PIOCPStruct);
begin
  FLock.Enter;
  try
    AValue.Assigned := False;
    AValue.Active := False;
  finally
    FLock.Leave;
  end;
end;

{ TServerSocket }

constructor TServerSocket.Create;
begin
  FMemory := TMemoryManager.Create(Self);
  FClients := TList.Create;
  FThreads := TList.Create;
  FSocket := INVALID_SOCKET;
  FLock := TCriticalSection.Create;

  FPort := 6666;
  FAcceptThread := nil;
  FIOCPHandle := 0;
  FHandle := AllocateHWnd(WndProc);
end;

destructor TServerSocket.Destroy;
begin
  //关闭完成端口
  SetActive(False);
  FThreads.Free;
  FClients.Free;
  DeallocateHWnd(FHandle);
  FMemory.Free;
  FLock.Free;
  inherited;
end;

procedure TServerSocket.Open;
var
  SystemInfo: TSystemInfo;
  i: Integer;
  Thread: TThread;
  Addr: TSockAddr;
  WSData: TWSAData;
begin
  try
    if WSAStartup($0202, WSData) <> 0 then
    begin
      raise ESocketError.Create('WSAStartup');
    end;
    DoLog(seInitIOPort);  //初始化完成端口
    FIOCPHandle := CreateIoCompletionPort(INVALID_HANDLE_VALUE, 0, 0, 0);
    if FIOCPHandle = 0 then
      CheckError;

    DoLog(seInitThread); //初始化工作线程
    GetSystemInfo(SystemInfo);
    for i := 0 to SystemInfo.dwNumberOfProcessors * 2 -1 do
    begin
      Thread := TWorkThread.Create(Self);
      FThreads.Add(Thread);
    end;

    DoLog(seInitSocket); //建立套接字
    FSocket := WSASocket(PF_INET, SOCK_STREAM, 0, nil, 0, WSA_FLAG_OVERLAPPED);
    if FSocket = INVALID_SOCKET then CheckError;

    FillChar(Addr, SizeOf(TSockAddr), 0);
    Addr.sin_family := AF_INET;
    Addr.sin_port := htons(FPort);
    Addr.sin_addr.S_addr := htonl(INADDR_ANY);
    CheckError(bind(FSocket, @Addr, SizeOf(TSockAddr)), 'bind');

    DoLog(seListen);  //开始监听
    CheckError(listen(FSocket, 5), 'listen');
    FAcceptThread := TAcceptThread.Create(Self);
  except
    on E: Exception do
    begin
      Close;
      CheckError(GetLastError, E.Message);
    end;
  end;
end;

procedure TServerSocket.Close;
var
  i: Integer;
  Thread: TThread;
begin
  try
    WSACleanup;
    DoLog(seUninitSocket);
    FAcceptThread.Terminate;
    if FSocket <> INVALID_SOCKET then
    begin
      closesocket(FSocket);
      FSocket := INVALID_SOCKET;
    end;

    DoLog(seUninitThread);
    for i := FThreads.Count - 1 downto 0 do
    begin
      Thread := FThreads[i];
      Thread.Terminate;
      PostQueuedCompletionStatus(FIOCPHandle, 0, 0, Pointer(SHUTDOWN_FLAG))
    end;
    FThreads.Clear;

    for i := FClients.Count - 1 downto 0 do
    begin
      TSymmetricalSocket(FClients[i]).Free;
    end;
    FClients.Clear;

    DoLog(seUninitIOPort);
    CloseHandle(FIOCPHandle);
    FIOCPHandle := 0;
  except
    on E: Exception do
    begin
      Close;
      CheckError(-1, E.Message);
    end;
  end;
end;

procedure TServerSocket.SetActive(AValue: Boolean);
begin
  if FActive = AValue then Exit;
  FActive := AValue;
  if FActive then
    Open
  else
    Close;
end;

procedure TServerSocket.WndProc(var AMsg: TMessage);
begin
  try
    Dispatch(AMsg);
  except
    if Assigned(ApplicationHandleException) then
      ApplicationHandleException(Self);
  end;
end;

function TServerSocket.CheckError(AErrorCode: Integer; AInfo: string): Boolean;
var
  HandleError: Boolean;
begin
  Result := True;
  if AErrorCode = 0 then Exit;
  if AErrorCode = -1 then
    AErrorCode := WSAGetLastError;
  if AErrorCode = -1 then
    AErrorCode := GetLastError;
  if (AErrorCode <> WSAEWOULDBLOCK) and (AErrorCode <> ERROR_IO_PENDING) and
    (AErrorCode <> 0) then
  begin
    if Assigned(FOnError) then
    begin
      HandleError := False;
      FOnError(AErrorCode, SysErrorMessage(AErrorCode), AInfo, HandleError);
      if HandleError then Exit;
    end;
    raise ESocketError.CreateFmt(SWindowsSocketError,
       [SysErrorMessage(AErrorCode), AErrorCode, AInfo]);
  end;
end;

procedure TServerSocket.DoLog(ASocketEvent: TSocketEvent; AInfo: string);
begin
  if Assigned(FOnLog) then FOnLog(ASocketEvent, AInfo);
end;

procedure TServerSocket.DoRead(ASymmetricalSocket: TSymmetricalSocket;
  AData: Pointer; ACount: Integer);
begin
  if Assigned(FOnRead) then
    FOnRead(ASymmetricalSocket, AData, ACount);
end;

procedure TServerSocket.SetPort(AValue: Integer);
begin
  if FActive then
    raise ESocketError.Create('IOCP is acitve, cann''t change port');
  FPort := AValue;
end;

procedure TServerSocket.RegisterClient(ASocket: TSymmetricalSocket);
begin
  FLock.Enter;
  try
    if FClients.IndexOf(ASocket) = -1 then
    begin
      FClients.Add(ASocket);
      DoAfterConnect(ASocket);
      {* 注册关闭通知消息 *}
      WSAAsyncSelect(ASocket.Socket, FHandle, WM_CLIENTSOCKET, FD_CLOSE);
    end;
  finally
    FLock.Leave;
  end;
end;

procedure TServerSocket.UnRegisterClient(ASocket: TSymmetricalSocket);
var
  iIndex: Integer;
begin
  FLock.Enter;
  try
    iIndex := FClients.IndexOf(ASocket);
    if iIndex <> -1 then
    begin
      FClients.Delete(iIndex);
      DoDisConnect(ASocket);
    end;
  finally
    FLock.Leave;
  end;
end;

procedure TServerSocket.AcceptClient;
var
  Addr: TSockAddrIn;
  iAddrLen: Integer;
  ClientWinSocket: TSocket;
  SymmSocket: TSymmetricalSocket;
begin
  iAddrLen := SizeOf(TSockAddrIn);
  ClientWinSocket := WinSock2.WSAAccept(Socket, nil, nil, nil, 0);
  if ClientWinSocket <> INVALID_SOCKET then
  begin
    if (not Active) or (not DoConnect(ClientWinSocket)) then
    begin
      closesocket(ClientWinSocket);
      Exit;
    end;
    try
      DoLog(seAccept);
      SymmSocket := TSymmetricalSocket.Create(Self, ClientWinSocket);
      DoLog(seConnect);
    except
      closesocket(ClientWinSocket);
      CheckError;
      Exit;
    end;
    if CreateIoCompletionPort(ClientWinSocket, FIOCPHandle, DWORD(SymmSocket), 0) = 0 then
    begin
      CheckError(GetLastError, 'CreateIoCompletionPort');
      SymmSocket.Free;
    end
    else
      SymmSocket.PrepareRecv;
  end;
end;

procedure TServerSocket.DoAfterConnect(ASymSocket: TSymmetricalSocket);
begin
  if Assigned(FOnAfterConnect) then FOnAfterConnect(ASymSocket);
end;

function TServerSocket.DoConnect(ASocket: TSocket): Boolean;
var
  SockAddrIn: TSockAddrIn;
  Size: Integer;
begin
  Result := True;
  if Assigned(FOnBeforeConnect) then
  begin
    Size := SizeOf(TSockAddrIn);
    CheckError(getpeername(ASocket, SockAddrIn, Size), 'getpeername');
    FOnBeforeConnect(inet_ntoa(SockAddrIn.sin_addr), Result);
  end;
end;

procedure TServerSocket.DoDisConnect(ASymSocket: TSymmetricalSocket);
begin
  if Assigned(FOnAfterDisconnect) then FOnAfterDisconnect(ASymSocket);
end;

function TServerSocket.FindSymmClient(
  ASocket: TSocket): TSymmetricalSocket;
var
  i: Integer;
begin
  Result := nil;
  FLock.Enter;
  try
    for i := 0 to FClients.Count - 1 do
    begin
      Result := FClients[i];
      if ASocket = Result.Socket then
        Break
      else
        Result := nil;
    end;
  finally
    FLock.Leave;
  end;
end;

function TServerSocket.GetClient(const AIndex: Integer): TSymmetricalSocket;
begin
  Result := FClients[AIndex];
end;

function TServerSocket.GetClientCount: Integer;
begin
  Result := FClients.Count;
end;

procedure TServerSocket.WMClientClose(var AMsg: TCMSocketMessage);
var
  ASymmSocket: TSymmetricalSocket;
begin
  if AMsg.SelectEvent = FD_CLOSE then
  begin
    ASymmSocket := FindSymmClient(AMsg.Socket);
    if Assigned(ASymmSocket) then
      ASymmSocket.Free;
  end;
end;

{ TSocketThread }

constructor TSocketThread.Create(AServer: TServerSocket);
begin
  FServer := AServer;
  inherited Create(False);
  FreeOnTerminate := True;
end;

{ TAcceptThread }

procedure TAcceptThread.Execute;
begin
  inherited;
  while not Terminated and FServer.Active do
  begin
    FServer.AcceptClient;
  end;
end;

{ TWorkThread }

procedure TWorkThread.Execute;
var
  ASymSocket: TSymmetricalSocket;
  AIOCPStruct: PIOCPStruct;
  iWorkCount: Cardinal;
begin
  inherited;
  while (not Terminated) and (FServer.Active) do
  begin
    AIOCPStruct := nil;
    iWorkCount := 0;
    ASymSocket := nil;
    if not GetQueuedCompletionStatus(FServer.FIOCPHandle, iWorkCount,
      DWORD(ASymSocket), POVerlapped(AIOCPStruct), INFINITE) then
    begin
      if Assigned(ASymSocket) then
        FreeAndNil(ASymSocket);
      Continue;
    end;

    if Cardinal(AIOCPStruct) = SHUTDOWN_FLAG then Break; //退出标志
    if not FServer.Active then Break; //退出

    {* 客户可能超时 或是断开连接，I/O失败 应放在通知结束的后面 *}
    if iWorkCount = 0 then
    begin
      //FreeAndNil(ASymSocket);  //不在这儿释放，而是接收释放消息来释放
      Continue;
    end;
    FServer.DoLog(AIOCPStruct.Event);
    if ASymSocket.WorkBlock(AIOCPStruct, iWorkCount) = -1 then
    begin
      FreeAndNil(ASymSocket);
    end;
  end;
end;

{ TSymmetricalSocket }

constructor TSymmetricalSocket.Create(ASvrSocket: TServerSocket;
  ASocket: TSocket);
begin
  FServer := ASvrSocket;
  FSocket := ASocket;
  FAssignMemory := TList.Create;
  FServer.RegisterClient(Self);
  //PrepareRecv;
end;

destructor TSymmetricalSocket.Destroy;
var
  i: Integer;
  Linger: TLinger;
begin
  FServer.UnRegisterClient(Self);
  FillChar(Linger, SizeOf(TLinger), 0);     //优雅关闭
  setsockopt(FSocket, SOL_SOCKET, SO_LINGER, @Linger, Sizeof(Linger));
  closesocket(FSocket);
  for i := FAssignMemory.Count - 1 downto 0 do
    FServer.MemoryManager.Release(FAssignMemory[i]);
  FAssignMemory.Free;
  inherited;
end;

function TSymmetricalSocket.Allocate: PIOCPStruct;
var
  i: Integer;
begin
  for i := 0 to FAssignMemory.Count - 1 do
  begin
    Result := FAssignMemory[i];
    if not Result.Active then
    begin
      Result.Active := True;
      Exit;
    end;
  end;
  Result := FServer.MemoryManager.Allocate;
  FAssignMemory.Add(Result);
  Result.Active := True;
end;

function TSymmetricalSocket.PrepareRecv(AIOCPStruct: PIOCPStruct = nil): Boolean;
var
  iFlags, iTransfer: Cardinal;
  ErrCode: Integer;
begin
  if not Assigned(AIOCPStruct) then
    AIOCPStruct := Allocate;
  iFlags := 0;
  AIOCPStruct.Event := seRead;
  FillChar(AIOCPStruct.Buffer, SizeOf(AIOCPStruct.Buffer), 0);
  FillChar(AIOCPStruct.Overlapped, SizeOf(AIOCPStruct.Overlapped), 0);
  AIOCPStruct.wsaBuffer.buf := @AIOCPStruct.Buffer;
  AIOCPStruct.wsaBuffer.len := MAX_BUFSIZE;
  Result := WSARecv(FSocket, @AIOCPStruct.wsaBuffer, 1, @iTransfer, @iFlags, @AIOCPStruct.Overlapped, nil) <> SOCKET_ERROR;
  if not Result then
  begin
    ErrCode := WSAGetLastError;
    Result := ErrCode = ERROR_IO_PENDING;
    if not Result then
      FServer.CheckError(ErrCode, 'WSARecv');
  end;
end;

function TSymmetricalSocket.WorkBlock(AIOCPStruct: PIOCPStruct;
  ACount: DWORD): Integer;
var
  ErrCode: Integer;
  iSend, iFlag: Cardinal;
begin
  Result := 0;
  try
    case AIOCPStruct.Event of
      seRead:  //接收数据
      begin
        FServer.DoRead(Self, @AIOCPStruct.Buffer[0], ACount);
        if PrepareRecv(AIOCPStruct) then
          Result := ACount;
      end;
      seWrite: //发送数据
      begin
        Dec(AIOCPStruct.wsaBuffer.len, ACount);
        if AIOCPStruct.wsaBuffer.len <= 0 then
        begin
          AIOCPStruct.Active := False;
        end
        else
        begin
          FillChar(AIOCPStruct.Overlapped, SizeOf(AIOCPStruct.Overlapped), 0);
          iFlag := 0;
          if SOCKET_ERROR = WSASend(FSocket, @AIOCPStruct.wsaBuffer, 1, @iSend,
            iFlag, @AIOCPStruct.Overlapped, nil) then
          begin
            ErrCode := WSAGetLastError;
            if ErrCode <> ERROR_IO_PENDING then
              FServer.CheckError(ErrCode, 'WSASend');
          end
          else Result := iSend;
        end;
      end;
    end;
  except
    Result := 0;
  end;
end;

function TSymmetricalSocket.Write(var ABuf; ACount: Integer): Integer;
var
  AIOCPStruct: PIOCPStruct;
  ErrCode: Integer;
  iFlag, iSend: Cardinal;
begin
  Result := ACount;
  if Result = 0 then Exit;
  AIOCPStruct := Allocate;
  iFlag := 0;
  AIOCPStruct.Event := seWrite;
  FillChar(AIOCPStruct.Buffer[0], SizeOf(AIOCPStruct.Buffer), 0);
  CopyMemory(@AIOCPStruct.Buffer[0], @ABuf, ACount);
  AIOCPStruct.wsaBuffer.buf := @AIOCPStruct.Buffer[0];
  AIOCPStruct.wsaBuffer.len := Result;

  if SOCKET_ERROR = WSASend(FSocket, @AIOCPStruct.wsaBuffer, 1, @iSend, iFlag,
    @AIOCPStruct.Overlapped, nil) then
  begin
    ErrCode := WSAGetLastError;
    if ErrCode <> ERROR_IO_PENDING then
    begin
      Result := SOCKET_ERROR;
      FServer.CheckError(ErrCode, 'WSASend');
    end;
  end;
end;

function TSymmetricalSocket.WriteString(const AValue: string): Integer;
begin
  Result := Write(Pointer(AValue)^, Length(AValue));
end;

function TSymmetricalSocket.GetRemoteIP: string;
var
  SockAddrIn: TSockAddrIn;
  iSize: Integer;
  HostEnt: PHostEnt;
begin
  if FRemoteAddress = '' then
  begin
    iSize := SizeOf(SockAddrIn);
    FServer.CheckError(getpeername(FSocket, SockAddrIn, iSize), 'getpeername');
    FRemoteAddress := inet_ntoa(SockAddrIn.sin_addr);
  end;
  Result := FRemoteAddress;
end;

function TSymmetricalSocket.GetRemotePort: Integer;
var
  SockAddrIn: TSockAddrIn;
  iSize: Integer;
  HostEnt: PHostEnt;
begin
  if FRemoteAddress = '' then
  begin
    iSize := SizeOf(SockAddrIn);
    FServer.CheckError(getpeername(FSocket, SockAddrIn, iSize), 'getpeername');
    FRemotePort := ntohs(SockAddrIn.sin_port);
  end;
  Result := FRemotePort;
end;

function TSymmetricalSocket.GetRemoteHost: string;
var
  SockAddrIn: TSockAddrIn;
  iSize: Integer;
  HostEnt: PHostEnt;
begin
  if FRemoteAddress = '' then
  begin
    iSize := SizeOf(SockAddrIn);
    FServer.CheckError(getpeername(FSocket, SockAddrIn, iSize), 'getpeername');
    HostEnt := gethostbyaddr(@SockAddrIn.sin_addr.S_addr, 4, PF_INET);
    if HostEnt <> nil then FRemoteHost := HostEnt.h_name;
  end;
  Result := FRemoteHost
end;

end.

http://blog.sina.com.cn/s/blog_562349090100zufs.html