I just learned that creating and using a Vcl.TTimer from a worker thread is not thread safe. My worker thread works fine ‘most of the time’ using the Vcl.TTimer. I found a class TTimerThread based on events which works fine also, but I don’t know how to combine both classes that TTimerThread has access to the methods of my worker thread.

ExecuteTimed() will be called when the event occurs (3000ms).

Pseudo code:

uses TimerThread;

type
  TMyTimerThread = class( TTimerThread )
  protected
  procedure ExecuteTimed; override;
[...]



TMQTTClient = class(TThread)
private
  [...]
  fKeepAliveTimer:TTimer;                     // Works, but is ugly.
  fKeepAliveTimerThread:TMyTimerThread;       //  
  [...]


procedure TMyTimerThread.ExecuteTimed;
begin
  beep;   // Works fine!
end;

[...]

constructor TMQTTClient.Create(aHostname: string; aPort: integer; ClientID:String;aKeepAliveSeconds : word);
begin
  //init some stuff...
  fKeepAliveTimer:=TTimer.Create(nil); // ugly
  fKeepAliveTimer.Interval:=fKeepAliveSeconds * 1000;
  fKeepAliveTimer.OnTimer:=DoKeepAlive; // The function pointer which should be called ~ every xxxx ms. Works fine, but no thread safe.

  fKeepAliveTimerThread:=TMyTimerThread.Create();
  fKeepAliveTimerThread.Interval:=3000;
  //fKeepAliveTimerThread.ExecuteTimed := ?; //here I wish to assign a pointer to the ExecuteTimed method of MyTimerThread.

I could imagine solving it using TThread.Synchronize() in ExecuteTimed() which calls the instance of the worker thread like frmMain.myMqttWorkerClass.DoKeepAlive, but I am in doubt if this is the right way.