delphi tcp server on multi port hanged on close - delphi

Question

i used a multi port tcp server to receive some connections
like this
procedure TForm2.IdTCPServer1Execute(AContext: TIdContext);
var
aByte: Byte;
i,j , tmBodyFrameLength:integer;
myThread : tthread;
begin
if not Assigned( allOfflineStringList ) then
begin
allOfflineStringList := TStringlist.Create;
end;
allOfflineStringList.Clear;
case AContext.Binding.Port of
55000: begin {offline and image}
AContext.Connection.IOHandler.ReadBytes(data, 1099, False);
rowFrame :='';
for I := 0 to length(data)-1 do
begin
rowFrame := rowFrame + (data[i].ToHexString);
end;
newFrame := copy( rowFrame , 9 , maxInt );
allOfflineStringList.Append( newFrame );
TThread.Synchronize (TThread.CurrentThread,
procedure ()
begin
Label985.caption := 'Offline : ' + allOfflineStringList.Count.ToString ;
//Memo14.Lines.Add( datetimetostr(now) +':'+ newFrame );
form2.AbLED601.Tag := DateTimeToUnix(now);
form2.AbLED601.Checked := true;
end);
end;
55001: begin {tm online}
repeat
aByte := AContext.Connection.IOHandler.ReadByte;
if aByte=$C0 then
begin
SDRtmOnlineRowFrame2 := SDRtmOnlineRowFrame;
SDRtmOnlineRowFrame := '';
TThread.Synchronize (TThread.CurrentThread,
procedure ()
begin
form2.Memo14.Lines.Add('tm:'+ SDRtmOnlineRowFrame2 );
end);
end
else
begin
SDRtmOnlineRowFrame := SDRtmOnlineRowFrame + aByte.ToHexString;
end;
until true;
end;
55003: begin {beacon online}
repeat
aByte := AContext.Connection.IOHandler.ReadByte;
if aByte=$C0 then
begin
SDRtmOnlineBeaconRowFrame2 := SDRtmOnlineBeaconRowFrame;
SDRtmOnlineBeaconRowFrame := '';
TThread.Synchronize (TThread.CurrentThread,
procedure ()
begin
form2.Memo14.Lines.Add('beacon:'+ SDRtmOnlineBeaconRowFrame2 );
end);
end
else
begin
SDRtmOnlineBeaconRowFrame := SDRtmOnlineBeaconRowFrame + aByte.ToHexString;
end;
until true;
end;
end;
end;
every thing working good
but when data is receiving if i close the connection
app will hange and dont responding any more!
enable and disable is like this:
procedure TForm2.CheckBox6Click(Sender: TObject);
var
ic:integer;
allIpList : TStringList;
begin
AbLED412.Checked := CheckBox6.Checked;
if CheckBox6.Checked=true then
begin
IdTCPServer1.Active := False;
IdTCPServer1.Bindings.Clear;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55000;
end;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55001;
end;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55003;
end;
IdTCPServer1.Active := True;
IdTCPServer1.StartListening;
TIdStack.IncUsage;
try
allIpList := TStringList.Create;
GStack.AddLocalAddressesToList( allIpList );
memo14.lines.clear;
for ic := 0 to allIpList.Count-1 do
begin
memo14.lines.Add('Create tcp connection on ip : '+allIpList[ic]+' and port : 55000');
memo14.lines.Add('Create tcp connection on ip : '+allIpList[ic]+' and port : 55001');
memo14.lines.Add('Create tcp connection on ip : '+allIpList[ic]+' and port : 55003');
end;
finally
TIdStack.DecUsage;
end;
end
else
begin
IdTCPServer1.StopListening;
IdTCPServer1.Active := False;
IdTCPServer1.Bindings.Clear;
memo14.lines.clear;
end;
end;
also when data is receiving if i close the app it hanged again
but when sender disconnected closing the app dont make any problem
how can i fix this?

Answer 1

Your TIdTCPServer.OnExecute handler is using multiple variables in a thread-unsafe manner. You are not protecting them from multiple threads accessing them at the same time, thus causing race conditions on their data.
But, more importantly, your use of TThread.Synchronize() is a common cause of deadlock for TIdTCPServer because it is a multi-threaded component. Its OnConnect, OnDisconnect, OnExecute, and OnError events are called in the context of client worker threads, not in the main UI thread. TThread.Synchronize() blocks the calling thread until the main UI thread processes the request. Deactivating TIdTCPServer terminates all running client threads and waits for them to fully terminate. So, if you call TThread.Synchronize() in a client thread while the main UI thread is blocked deactivating the server, then the client thread is waiting on the main UI thread while the main UI thread is waiting on the client thread - deadlock!
You have a few options to solve this:
avoid calling TThread.Synchronize() while deactivating the server. Easier said than done though, as you might already be in a pending TThread.Synchronize() by the time you decide to deactivate TIdTCPServer. And it is a race condition when making the decision whether to call TThread.Synchronize() or not.
deactivate TIdTCPServer in a separate worker thread, leave the main UI thread free to process TThread.Synchronize() and TThread.Queue() requests. If you use a TThread for the deactivation, calling the TThread.WaitFor() method in the main UI thread will process Synchronize()/Queue() requests while it is waiting for the thread to terminate.
Use TThread.Queue() instead of TThread.Synchronize(), especially when performing actions that your client threads don't actually need to wait on, such as UI updates.
On a side note, in your CheckBox6Click():
you should not be calling TIdTCPServer.StartListening() or TIdTCPServer.StopListening() at all. The TIdTCPServer.Active property setter calls them internally for you.
you don't need to call TIdStack.IncUsage() or TIdStack.DecUsage() either, as TIdTCPServer's constructor and destructor call them for you.
you are leaking allIpList as you don't Free() it. And TIdStack.AddLocalAddressesToList() is deprecated anyway, you should be using TIdStack.GetLocalAddressList() instead.
Try this:
procedure TForm2.CheckBox6Click(Sender: TObject);
var
ic: integer;
allIpList : TIdStackLocalAddressList;
begin
AbLED412.Checked := CheckBox6.Checked;
if CheckBox6.Checked then
begin
IdTCPServer1.Active := False;
IdTCPServer1.Bindings.Clear;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55000;
end;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55001;
end;
with IdTCPServer1.Bindings.Add do
begin
//IP := '192.168.1.5';
Port := 55003;
end;
IdTCPServer1.Active := True;
allIpList := TIdStackLocalAddressList.Create;
try
GStack.GetLocalAddressesList( allIpList );
Memo14.Lines.Clear;
{
for ic := 0 to IdTCPServer1.Bindings.Count-1 do
begin
Memo14.Lines.Add('Create tcp connection on ip : ' + IdTCPServer1.Bindings[ic].IP + ' and port : ' + IntToStr(IdTCPServer1.Bindings[ic].Port));
end;
}
for ic := 0 to allIpList.Count-1 do
begin
if allIpList[ic].IPVersion = ID_DEFAULT_IP_VERSION then
begin
Memo14.Lines.Add('Create tcp connection on ip : ' + allIpList[ic].IPAddress + ' and port : 55000');
Memo14.Lines.Add('Create tcp connection on ip : ' + allIpList[ic].IPAddress + ' and port : 55001');
Memo14.Lines.Add('Create tcp connection on ip : ' + allIpList[ic].IPAddress + ' and port : 55003');
end;
end;
finally
allIpList.Free;
end;
end
else
begin
IdTCPServer1.Active := False;
IdTCPServer1.Bindings.Clear;
Memo14.Lines.Clear;
end;
end;