I noticed, that when a tcp server accepts a connection and finally the connection is closed, either when the client disconnects, or the server closes the connection, there remains a file descriptor open! Using lsof, or in /proc/(processID)/fd, I can see the file descriptor. At first I thought that the file descriptor whould be there, as long as the connection would be in TIME_WAIT state, but I was wrong.

Is this behaviour normal?

If the server accepts connections at fast rates, then the result is Too many open files Errors...

I only use one process to handle multiple client connections. I wanted to confirm it and used a very simple similar program and the result is the same...

Here is the code I used to confirm it...

Uses Sockets;
Var
     lSock : LongInt;
     uSock : LongInt;
     sAddr : TInetSockAddr;
     lLen  : LongInt;
     sLine : String;
     SIn   : Text;
     SOut  : Text;
Procedure PError (Const S : String);
Begin
     Writeln (S, SocketError);
     Halt (100);
End;
Begin
     lSock:=Socket (AF_Inet, Sock_Stream, PF_Unspec);
     If SocketError0 Then PError ('Server : Socket : ');
     sAddr.Family:=AF_Inet;
     sAddr.Port  :=lo (3000) shl 8 or hi (3000);
     sAddr.Addr  :=(1 shl 24) or 127;
     If Not Bind (lSock, sAddr, SizeOf (sAddr)) Then PError ('Server : Bind');
     If Not Listen (lSock, 1) Then PError ('Server : Listen : ');
     Repeat
          Writeln ('Accepting connection...');
          lLen :=SizeOf (sAddr);
          uSock:=Accept (lSock, sAddr, lLen);
          If SocketError0 Then PError ('Server : Accept : ');
          Writeln ('Connection accepted...');
          Sock2Text (USock, SIn, SOut);
          Reset (SIn);
          Rewrite (SOut);
          While Not Eof (SIn) Do
          Begin
               ReadLn  (SIn, sLine);
               write   (sout,sline);
               writeln (sline);
          End;
          Close (Sin);
          Close (SOut);
          ShutDown (uSock, 2);
     Until False;
End.

Try adding a close of the socket fd after the shutdown:

fdClose(uSock);

This is normal. The solution to this should be a call to setsockopt() with the SO_REUSEADDR option.

Michael.