Question

I am using TIdTCPClient to get a file list all works well but when i close the client application and open it again i don’t receive any event on TCPServer onExecute though the TIdTCPClient successfully connects to it and i am not able to send the file list.

What am i doing wrong ?

Some code :

procedure TTaifun.csConnected(Sender: TObject);
begin
  cs.IOHandler.WriteLn('FILE_LIST|NOW'); //Sending a request to server for the files
  fname := cs.IOHandler.ReadLn(nil); //Got the file names
  files := ExplodeString(fname,'|'); // Parse the files
end;

procedure TTaifun.svExecute(AContext: TIdContext);
var
  cmds, flist: TStringList;
  i: Integer;
  tmp: string;
  FS : TFileStream;
begin
  CSection.Enter; //Enter critical section
  cmds := ExplodeString(AContext.Connection.IOHandler.ReadLn(nil), '|'); 
  try
    if cmds[0] = 'FILE_LIST' then //Check command received
    begin
      flist := TStringList.Create;
      flist.LoadFromFile(MyPath + 'files.dat');
      tmp := '';
      for i := 0 to flist.Count - 1 do
      begin
          tmp := tmp + flist[i] + ',' + GetFileSize(flist[i]) + ',' +
          BoolToStr(FileExists(MyPath + 'Thumbs\' +
          ChangeFileExt(ExtractFileName(flist[i]), '.thb')),true) + '|'; //Do some parsing
      end;
      AContext.Connection.IOHandler.WriteLn(tmp); //Send the string
    end
 finally
  CSection.Leave; //Leave critical section
 end;
end;

Answer 1

You are not protecting your critical section from exceptions. When the client disconnects, an exception will be raised by either ReadLn() or WriteLn() (depending on timing) to terminate the thread for that client. The next time the OnExecute event is called for a different thread, the critical section will still be locked and cannot be re-entered again, deadlocking your code. Add a try/finally to your code to guard against that, eg:

procedure TTaifun.svExecute(AContext: TIdContext); 
var 
  ...
begin 
  CSection.Enter; //Enter critical section 
  try
    ...
  finally
    CSection.Leave; //Leave critical section 
  end;
end; 

With that said, why are you using a critical section to begin with? The code you showed is thread-safe by itself, it does not need to be protected from concurrent access:

procedure TTaifun.svExecute(AContext: TIdContext);     
var     
  cmds, flist: TStringList;     
  i: Integer;     
  tmp: string;     
begin     
  cmds := ExplodeString(AContext.Connection.IOHandler.ReadLn, '|');      
  if cmds[0] = 'FILE_LIST' then //Check command received     
  begin     
    tmp := '';     
    flist := TStringList.Create;     
    try
      flist.LoadFromFile(MyPath + 'files.dat');     
      for i := 0 to flist.Count - 1 do     
      begin     
        tmp := tmp + flist[i] + ',' + GetFileSize(flist[i]) + ',' +     
          BoolToStr(FileExists(MyPath + 'Thumbs\' +     
          ChangeFileExt(ExtractFileName(flist[i]), '.thb')),true) + '|'; //Do some parsing     
      end;
    finally
      flist.Free;
    end;     
    AContext.Connection.IOHandler.WriteLn(tmp); //Send the string     
  end;
end;

Alternatively:

procedure TTaifun.svExecute(AContext: TIdContext);     
var     
  cmds, flist: TStringList;     
  i: Integer;     
begin     
  cmds := ExplodeString(AContext.Connection.IOHandler.ReadLn, '|');      
  if cmds[0] = 'FILE_LIST' then //Check command received     
  begin     
    flist := TStringList.Create;     
    try
      flist.LoadFromFile(MyPath + 'files.dat');     
      for i := 0 to flist.Count - 1 do     
      begin     
        flist[i] := flist[i] + ',' + GetFileSize(flist[i]) + ',' +     
          BoolToStr(FileExists(MyPath + 'Thumbs\' +     
          ChangeFileExt(ExtractFileName(flist[i]), '.thb')),true); //Do some parsing     
      end;
      flist.Delimiter := '|';
      flist.StrictDelimiter := True;
      AContext.Connection.IOHandler.WriteLn(flist.DelimitedText); //Send the string     
    finally
      flist.Free;
    end;     
  end;
end;