我觉得这是一个非常有意思的问题，我使着写了一下：）
closesocket语句的执行效果是与“套接字选项(socket option)”的设置相关的，具体的
是受SO_LINGER 和 SO_DONTLINGER影响效果为(通过查MSDN得到的):
Option Interval Type of close Wait for close?
SO_DONTLINGER Do not care Graceful No
SO_LINGER Zero Hard No
SO_LINGER Nonzero Graceful Yes
我们在关闭套接字时为了处理还未接受到的数据，所以不马上关闭连接(hard方式)
当然你可以强行关闭连接(即以hard方式)。套接字选项(socket option)可以通过方法
setsockopt来设置，该方法在delphi中的原型为：
function setsockopt(s: TSocket; level, optname: Integer; optval: PChar;
optlen: Integer): Integer;
你如果想在连接关闭后马上关闭连结则需设置SO_LINGER的间隔(Interval)为0就可以了
如：
var
t:linger;
t.l_onoff := 1;
t.l_linger := 0;
Re := setsockopt(sckt,SOL_SOCKET,SO_LINGER,@t,sizeof(t)) ;
我写的测试的例子如下，可能乱了一点：
procedure TForm1.Button1Click(Sender: TObject);
var
sckt:TSocket;
WSAData:TWSAData;
addr:TSockAddr;
Re,err:Integer;
Info:string;
t : linger;
begin
if (WSAStartup(MAKEWORD(2,0),WSAData)<>0)then
begin
memo1.Lines.Add('Winsock Init Failed');
exit;
end
else
memo1.Lines.Add('Socket Start');
//-----------------//
sckt:=socket(AF_INET,SOCK_STREAM,0);
if(sckt=INVALID_SOCKET)then
begin
memo1.Lines.Add('Erro:Create socket failed!');
exit;
end;
//--------设置套接字选项-------//
t.l_onoff := 1;
t.l_linger := 0;
Re := setsockopt(sckt,SOL_SOCKET,SO_LINGER,@t,sizeof(t)) ;
//----------以下是相应的错误信息，是直接从MSDN中粘过来的，有点乱------//
if Re = SOCKET_ERROR then
begin
err:=WSAGetLastError();
case err of
WSANOTINITIALISED : Info:='A successful WSAStartup call must occur before using this function.';
WSAENETDOWN : Info:='The network subsystem has failed. ';
WSAEFAULT : Info:='The optval parameter is not in a valid part of the process address space or the optlen parameter is too small. ';
WSAEINPROGRESS : Info:='A blocking Winsock call is in progress, or the service provider is still processing a callback function. ';
WSAEINVAL : Info:='The level parameter is not valid, or the information in optval is not valid. ';
WSAENETRESET : Info:='The connection has timed out when SO_KEEPALIVE is set. ';
WSAENOPROTOOPT : Info:='The option is unknown or unsupported for the specified provider or the socket ';
WSAENOTCONN : Info:='The connection has been reset when SO_KEEPALIVE is set';
WSAENOTSOCK : Info:='The descriptor is not a socket';
end;
end
else
Info:='Set socket option ok!';
memo1.Lines.Add(Info);
//------------//
ZeroMemory(@addr,sizeof(addr));
addr.sin_family:=AF_INET;
addr.sin_addr.S_addr :=inet_addr(Pchar(edit1.Text));
addr.sin_port :=htons(StrToInt(edit2.Text));
Re:=connect(sckt,addr,sizeof(addr));
if(Re<>0)then
begin
memo1.Lines.Add('Connect to server failed');
exit;
end
else
Memo1.Lines.Add('Connect to server Success');
//----------关闭套接字--------//
Re:=closesocket(sckt);
if Re=SOCKET_ERROR then
begin
err:=WSAGetLastError();
case err of
WSANOTINITIALISED : Info:='A successful WSAStartup call must occur before using this function.';
WSAENETDOWN : Info:='The network subsystem has failed. ';
WSAEFAULT : Info:='The optval parameter is not in a valid part of the process address space or the optlen parameter is too small. ';
WSAEINPROGRESS : Info:='A blocking Winsock call is in progress, or the service provider is still processing a callback function. ';
WSAEINTR : Info:='Canceled through WSACancelBlockingCall';
WSAEWOULDBLOCK : Info:='time-out value to large';
end;
end
else
Info:='Close socket success';
memo1.Lines.Add(Info);
WSACleanUP();
end;
当运行上面的例子时，你再用netstat -an来试一下会发现socket是立刻关闭的，如果设置选项为
SOL_DONTLINGER或关闭LINGER(通过设置t.l_onoff=0)则会发想socket会继续等待。并且通过
上面对套接字选项SO_LINGER的说明我们还可以设置wait的时间，如等待1000秒：
t.l_onoff := 1;
t.l_linger := 1000;
//--------设置套接字选项-------//
Re := setsockopt(sckt,SOL_SOCKET,SO_LINGER,@t,sizeof(t)) ;
关于这个等待时间的设置是有问题的，因为通过测试发现与MSDN中的说明不符，好像不起作用.
