Delphi - a communication thread

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A communication thread

It is quite common that communication is a sequence of messages where the sequence matters. Communication applications are special in this respect as messages can disappear. This means, it can be a requirement to have the replies of previous messages before issuing the next. This functionality is best done with a thread. The messages to be sent come from various events, timer, buttons, whatver and are gathered with a Queue.

{

formcreate:
 CQ:=TSimpleMsgQueue.create;
 CommThread.queue:=CQ;
 CommThread.sp:=sp;
 Commthread.lostpackets:=0;
 CS:=TCommThread.create(false);
 rxcame:=true;

procedure TForm1.SendMsgClick(Sender: TObject);
var u:TMyMsg;
    s,v:shortstring;
    i,j:integer;
begin
 s:=a_command;
 v:=just_a_header+s;
 calcCRC(v);
 v:=header+v;
 i:=length(v);
 u:=TMyMsg.create(i);
 u.asstring:=v;
 u.delay:=0;
 CQ.queuein(u);
end;

procedure TForm1.MakeDelayClick(Sender: TObject);
var u:TMyMsg;
    i,j:integer;
begin
 u:=TMyMsg.create(0);
 u.delay:=1000;
 CQ.queuein(u);
end;

}

unit CommThread;

interface

uses
  Windows,Classes,StdCtrls,MyMsgQueue,OoMisc,Adport;

const
 //mtimeout=500;
 sleeptime=50;

type
  TCommThread = class(TThread)
  private
    { Private declarations }
  protected
    procedure Execute; override;
    procedure send;
  end;

VAR queue:TSimpleMsgQueue;
 sp: TApdComPort;
 h:shortstring;
 rxcame:boolean;
 rxstring:shortstring;
 rxstate:integer;
 lostpackets:integer;
 mtimeout:integer;
 ErrorLog:TMemo;
 PacketOrigin:integer;

implementation

uses mystrings;

{ Important: Methods and properties of objects in VCL can only be used in a
  method called using Synchronize, for example,

      Synchronize(UpdateCaption);

  and UpdateCaption could look like,

    procedure TCommThread.UpdateCaption;
    begin
      Form1.Caption := 'Updated in a thread';
    end; }

{ TCommThread }

procedure TCommThread.send;
begin
 sp.putstring(h);
end;


procedure TCommThread.Execute;
var p:TMyMsg;
 tcount:integer;
 z:shortstring;
begin
  { Place thread code here }
  tcount:=0;
 while not terminated do begin
  if (queue.count < > 0)and(rxcame) then begin
   p:=queue.queueout;
   h:=p.asstring;
   PacketOrigin:=p.origin;
   if (h < > '') then rxcame:=false; // empty packets are a delay only
   rxstring:='';
   rxstate:=0;
   tcount:=0;
   sleep(p.delay);   // wait before send
   sleep(50);
   synchronize(send);
   p.destroy;
   end;
  sleep(sleeptime);
  if (not rxcame) then begin
   inc(tcount);
   if ((tcount*sleeptime) > mtimeout) then begin
    inc(lostpackets);
    tcount:=0;
    synchronize(send);
    end;
   end;
 end; // while
end;

end.

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last updated: 12.april.04 or perhaps later

Copyright (99,2004) Ing.Büro R.Tschaggelar