Catch unhandled exceptions from a different thread

Question

I am writing an IPC application. I want to catch exceptions from process B silently and then send the exception details as string to process A. I am able to catch exceptions from main thread, but have problems to catch exceptions from a different thread.

procedure TForm1.ApplicationEvents1Exception(Sender: TObject; E: Exception);
begin
  SendExceptionToAnotherProcess(E.ToString);
end;

type
  AThread = class(TThread)
  protected
    procedure Execute; override;
  end;

procedure AThread.Execute; // Main thread cannot catch such runtime exception
var  uq1, uq2: UInt64;
     s1:       Single;
     d1:       Double;
begin
  uq1 := $9000000000000000;
  s1 := uq1;   // no problem here
  // exception class $C0000090 with message 'c0000090 FLOAT_INVALID_OPERATION'.
  uq2 := round(s1);   // but back-conversion crashes
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  T: AThread;
begin
  T := AThread.Create(True);
  T.Start;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  raise Exception.Create('I can catch it'); 
end;

Is there any way to catch exceptions from all threads? The exception might be thrown by 3rd library or ActiveX control in different threads.

Answer 1

I tried madExcept, which is able to catch exception from different thread. After further digging, I found a way to catch exceptions silently with the help of madExcept.

procedure TForm1.HandleUncaughtException(const ExceptIntf: IMEException; var Handled: Boolean);
begin
  SendExceptionToAnotherProcess(ExceptIntf.ExceptMessage);
  Handled := True;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  madExcept.RegisterExceptionHandler(HandleUncaughtException, stTrySyncCallAlways, epMainPhase);
end;

Answer 2

Though I know of MadExcept I have no personal experience with it, but the generic approach to catching exceptions in threads is to have a try...except frame in the thread's Execute method. In the except...end block you should then be able to call Form1.ApplicationEvent1Exception yourself.