Delphi 7 + Indy + Multithread clients - multithreading

Question

My PC is connected to two electronic devices that send data using a TCP connection. I would like to develop a Delphi program able to log all this data. In the following code I create two TCPClients using two threads. I am able to log data from one device using one thread, but when two threads are runnning the application freezes. I don´t have experience programming in Delphi, sorry if there are too many mistakes... I am using Delphi 7. What can I do to avoid freezing the app?
Thanks in advance
//************************************************************************//
type TThreadConn1 = class(TThread)
private
protected
procedure Execute; override;
end;
type TThreadConn2 = class(TThread)
private
protected
procedure Execute; override;
end;
var
Form1: TForm1;
TCP1: TThreadConn1;
TCP2: TThreadConn2;
flag1: bool;
flag2: bool;
implementation
{$R *.dfm}
//******************************Connection 1******************************//
procedure TThreadConn1.Execute; //Connect+loop read buffer+disconnect
begin
Form1.IdTCPClient1.Connect;
While flag1 = false do
Form1.IdTCPClient1.CurrentReadBuffer;
Form1.IdTCPClient1.Disconnect;
end;
procedure TForm1.ButtonConnection1Click(Sender: TObject);
begin
flag1:=false;
TCP1 := TThreadConn1.Create(false); //Launch thread
end;
procedure TForm1.ButtonDisconnection1Click(Sender: TObject);
begin
flag1:=true;
if (TCP1.Terminated = false) then
TCP1.Terminate; //Is it ok to finish this way a thread?
end;
//******************************Connection2******************************//
procedure TThreadConn2.Execute; //Connect+loop read buffer+disconnect
begin
Form1.IdTCPClient2.Connect;
While flag2 = false do
Form1.IdTCPClient1.CurrentReadBuffer;
Form1.IdTCPClient2.Disconnect;
end; { of procedure }
procedure TForm1.ButtonConnection2Click(Sender: TObject);
begin
flag2:=false;
TCP2 := TThreadConn2.Create(false);
end;
procedure TForm1.ButtonDisconnection2Click(Sender: TObject);
begin
flag2:=true;
if (TCP2.Terminated = false) then
TCP2.Terminate;
end;
end.

Answer 1

You don't need to create two separate threads that do the same thing. Create one class and then instantiate multiple copies of it. Try this instead:
type
TThreadConn = class(TThread)
private
FClient: TIdTCPClient;
protected
procedure Execute; override;
public
constructor Create(AClient: TIdTCPClient);
end;
var
TCP1: TThreadConn = nil;
TCP2: TThreadConn = nil;
constructor TThreadConn.Create(AClient: TIdTCPClient);
begin
inherited Create(False);
FClient := AClient;
end;
procedure TThreadConn.Execute;
begin
FClient.Connect;
try
while Terminated = false do
FClient.CurrentReadBuffer;
finally
FClient.Disconnect;
end;
end;
procedure TForm1.ButtonConnection1Click(Sender: TObject);
begin
TCP1 := TThreadConn.Create(TIdTCPClient1);
end;
procedure TForm1.ButtonDisconnection1Click(Sender: TObject);
begin
if (TCP1 <> nil) then
begin
TCP1.Terminate;
TCP1.WaitFor;
FreeAndNil(TCP1);
end;
end;
procedure TForm1.ButtonConnection2Click(Sender: TObject);
begin
TCP2 := TThreadConn.Create(IdTCPClient2);
end;
procedure TForm1.ButtonDisconnection2Click(Sender: TObject);
begin
if (TCP2 <> nil) then
begin
TCP2.Terminate;
TCP2.WaitFor;
FreeAndNil(TCP2);
end;
end;

Answer 2

Apart from the overall design, (which you will probably fix in time, maybe with some more help), in TThreadConn2.Execute, you call Form1.IdTCPClient1.CurrentReadBuffer.
Hints:
If you want to use threads to communicate with several different clients, don't plonk TidTCPClients onto forms. This is inflexible because every time you want to add a new client, you have to plonk another instance onto the form and rebuild. It also makes for a lot of extra work to get your app to shut down cleanly which, I assure you, you will not want.
Dynamically create a TidTCPClient instance in either the TThread descendant ctor or at the top of the 'Execute' method.
Try and declare one class that can be instantiated for each client connection, so you don't have to copy/paste code, edit it and and get it wrong
Oh - for now, don't try and terminate the threads at all. In fact, forever, don't try and terminate the threads at all. In the execute, loop around connect() until successful, then read stuff in a loop, write to log, (in a thread-safe manner). Do that forever. If you wnat to stop the logging, set a 'don't log' boolean so that the thread still runs but simply doesn't bother calling the logger. Again - don't go near trying to terminate the threads.
If I get a chance over the weekend, I'll do a simple example - one form, four TEdits for two pair hostname/port and two TMemos to send data to and display data from the server.