No route to host (was: Multiplexed Server-nClient architecture)
lazarus / 38-Networking and Web Programming

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Ocye · 2012-03-23 12:41

I was running a server with multiple threaded clients corresponding to
Synapse's echo demo for some time. But due to changes in data
management (and since Linux supports IMHO a maximum of 40 threads per
default) I want to change to a multiplexed design. Registration and
simple pass through messages work fine. But client's free isn't called
until server shutdown.

Am I completely wrong with my approach?

Code: [Select]TClient=class(TClientInfo)
    private
      FClientSocket: TTCPBlockSocket;//Synapse
      procedure DoStatus(Sender: TObject; Reason: THookSocketReason;
const Value: string);
    protected
      ParentList  : TList; //link to server.clients
    public
      constructor Create(aSocket:TSocket; aParentList:TList);
      destructor Destroy; override;
    end;

constructor TClient.Create(aSocket: TSocket; aParentList:TList);
begin
  inherited Create('');
  Release:='0.0';
  FClientSocket:=TTCPBlockSocket.Create;
  FClientSocket.Socket:=aSocket;
  FClientSocket.OnStatus:=@DoStatus;
  ParentList:=aParentList;
end;

destructor TClient.Destroy;
var
  i:integer;
begin
  writeln(DateTimeToStr(Now),': ',PlayerName,' freed');
  FreeAndNil(FClientSocket);
  i:=ParentList.IndexOf(self);
  if i>-1 then
    ParentList.Delete(i);
  inherited Destroy;
end;

procedure TClient.DoStatus(Sender: TObject; Reason: THookSocketReason;
const Value: string);
begin
  if (Reason=HR_SocketClose) then //and assigned(FClientSocket) then
  begin
    Free;
  end;
end;

Code: [Select]  TCustomTCPServer=class(TThread)
    private
      FClients  : TList;
      FServerSocket  : TTCPBlockSocket;
//      FRecvMsg=class(TStringList) ->
Values='Sender','Receiver','MessageType','Content' etc.
    protected
    public
      constructor Create(aPort:string);
      procedure Execute; override;
      property Clients : TList read FClients write FClients;
    end;

constructor TCustomTCPServer.Create(aPort:string);
begin
  inherited Create(true);
  FServerSocket:=TTCPBlockSocket.Create;
//  FServerSocket.EnableReuse(true);
  FreeOnTerminate:=true;
  FClients:=TList.Create;
  Start;//Resume;
end;

procedure TCustomTCPServer.Execute;
var
  i,j:integer;
  aSender,aReceiver:TClient;
begin
  FServerSocket.Bind('0.0.0.0', FPort);
  //FServerSocket.SetLinger(true, 10);
  if FServerSocket.LastError=0 then
  begin
    FServerSocket.Listen;
    while not Terminated do
    begin
      if FServerSocket.CanRead(100) then
      begin
        aSender:=TClient.Create(FServerSocket.Accept, FClients);
        FClients.Add(aSender);
      end;
      for i:=0 to FClients.Count-1 do
      begin
        aSender:=TClient(FClients[i]);
        if aSender.ClientSocket.CanRead(10) then
        begin
         
FRecvMsg.DelimitedText:=aSender.ClientSocket.RecvString(1000);
          DoSomeThingWithMsg();
          for j:=0 to FClients.Count-1 do
          begin
            aReceiver:=TClient(FClients[j]);
           
aReceiver.ClientSocket.SendString(FRecvMsg.DelimitedText+CRLF);
          end;//for to j
        end;
      end; //for to i
    end;//Terminated
  end else
    Terminate;//FSocket.LastError<>0
end;

Code: [Select]type
  TTCPServer=class(TCustomTCPServer)
  private
    mysql stuff
end;

  with TTCPServer.Create(cPort,_user,_passwd,_database) do
  try
    repeat
      sleep(10);
    until KeyPressed;
  finally
    Free; //TCPServer
  end;

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marcov · 2012-03-23 13:11

I don't know synapse very well, but how long did you wait? TCP/IP
timeouts are typically 8-10 minutes.

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Ocye · 2012-03-23 14:11

Client's socket fires HR_SocketClose² event which is connected 
(FClientSocket.OnStatus:=@DoStatus;). That was working well in
threaded environment.

[2] Ararat doc

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ludob · 2012-03-23 20:11

The HR_SocketClose is triggered when the socket is closed. In TClient
you wait for HR_SocketClose to close the socket which will never
happen. When the remote closes its side of the connection you'll get
an error status when trying to send or receive something on the
second. This error condition does not trigger a HR_SocketClose.
Canread calls select which doesn't not return error information but
when a the remote side closes the connection, it will trigger the
select for that socket. The next recv will return 0 however and
synapse will report WSAECONNRESET .
What you need to do is to check for WSAECONNRESET after
aSender.ClientSocket.RecvString(1000) and close the socket if true.
You should also test for the same error after
aReceiver.ClientSocket.SendString(FRecvMsg.DelimitedText+CRLF) because
there you can also encounter closed sockets.

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Ocye · 2012-03-24 16:48

Quote from: ludob on March 23, 2012, 09:11:22 pmWhat you need to do is
to check for WSAECONNRESET after RecvString(1000)..That works, At
least I recognize when a client has been disconnected gracefully.
Thanks!

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Ocye · 2012-04-15 10:28

I attach my new issue to this thread because I believe its related to
the architecture. With my first multithreaded approach I didn't run
into that trouble.

My service has some hiccups. It runs well for several hours but delays
all traffic for about 10-15min sometimes. My logging points to a
routing problem and some other strange (following) errors.
QuoteScrabble3D [2012-04-14 23:53:05.563 Debug] HR_ReadCount 50
(udostt)
Scrabble3D [2012-04-14 23:53:05.577 Info] : udostt->all: nwRefresh
(13ms)
Scrabble3D [2012-04-15 00:05:08.283 Debug] HR_WriteCount 1222 (PC
WINDOS)
Scrabble3D [2012-04-15 00:05:08.283 Debug] HR_ERROR 113,No route to
host (PC WINDOS)
Scrabble3D [2012-04-15 00:05:08.285 Error] PC WINDOS:No route to host
in 722707ms]
Scrabble3D [2012-04-15 00:05:08.286 Debug] HR_WriteCount 1486 (udostt)
Scrabble3D [2012-04-15 00:05:08.288 Debug] HR_WriteCount 1486
(bummi2005)
Scrabble3D [2012-04-15 00:05:08.289 Debug] HR_ERROR 32,Other Winsock
error (32) (Petronella)
Scrabble3D [2012-04-15 00:05:08.290 Error] Petronella:Other Winsock
error (32) in 1ms]
Scrabble3D [2012-04-15 00:05:08.291 Debug] HR_WriteCount 1486
(Linuxbussinchen)
Scrabble3D [2012-04-15 00:05:08.292 Debug] HR_WriteCount 1486 (opdio)
Scrabble3D [2012-04-15 00:05:08.292 Debug] HR_ERROR 32,Other Winsock
error (32) (Karl_B)
The player with name "PC WINDOS" is located in Tunesia so a "no route
to host" makes sense. But how can I catch this issue before the delay?
And, what does HR_ERROR 32 means? Should I care about? I believe
players have been logged out and in again (they couldn't know whether
server or client is responsible for a hiccup) and socket isn't
available anymore.

Minutes later I got a further delay but I don't have any idea for what
reason.
QuoteScrabble3D [2012-04-15 00:05:10.968 Info] : manou->group:
nwSyncNewGame (1ms)
Scrabble3D [2012-04-15 00:05:10.971 Debug] HR_WriteCount 1148 (manou)
Scrabble3D [2012-04-15 00:05:11.143 Debug] HR_CanRead  (manou)
Scrabble3D [2012-04-15 00:05:11.147 Info] : manou->group:
nwSyncNewGame (2ms)
Scrabble3D [2012-04-15 00:21:27.863 Debug] HR_WriteCount 478 (manou)
Scrabble3D [2012-04-15 00:21:27.864 Debug] HR_ERROR 110,Connection
timed out (manou)
Scrabble3D [2012-04-15 00:21:27.864 Error] manou:Connection timed out
in 976713ms]
Scrabble3D [2012-04-15 00:21:27.868 Debug] HR_CanRead  (Karl_B)
Scrabble3D [2012-04-15 00:21:27.869 Debug] HR_ReadCount 195 (Karl_B)
Scrabble3D [2012-04-15 00:21:27.879 Info] : Karl_B->all: nwRefresh
(9ms)
Scrabble3D [2012-04-15 00:21:27.880 Debug] HR_ERROR 32,Other Winsock
error (32) (Petronella)
Scrabble3D [2012-04-15 00:21:27.882 Error] Petronella:Other Winsock
error (32) in 1ms]
AFAIK manou is French, thus connection should be good. The only
problem I see is an internal question - nwSyncNewGame shouldn't be
sent twice. I add this second observation to question the "no route"
phenomenon.
All other traffic was okay for the last 12 hours.

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Ocye · 2012-04-17 15:58

I found the option SetTimeOut(). With a value of 5000 (I assume
milliseconds) for both server and client socket the connection times
out after 20000ms. Very strange.