CODEWITHSUNDEEP
delphitimeoutdelphi-xe2adoabort
Jerry Dodge
Jerry Dodge

Reputation: 27276

Cancel an ADO Connection's attempt to connect?

I have a TADOConnection inside a thread. In the event that it fails to connect to the database (timeout), when closing the app, the thread is held up and it takes time until the attempt is finished before my app is able to close. I don't want to reduce the connection timeout of the connection, this isn't the issue. Is there any way I can forcefully abort the attempt to connect?

The TADOConnection connects at the beginning of the thread execution and automatically reconnects repeatedly until success. Then, upon closing the app, if the database is failing to connect, the thread hangs until the connection attempt is finished (timed out).

EDIT

This is a sample of how the thread works:

procedure TMyThread.Init;
begin
  CoInitialize(nil);
  FDB:= TADOConnection.Create(nil);
  FDB.LoginPrompt:= False;
  FDB.ConnectionTimeout:= 5;
  FDB.ConnectOptions:= coAsyncConnect;
end;

procedure TMyThread.Uninit;
begin
  if FDB.Connected then
    FDB.Connected:= False;
  FDB.Free;
  CoUninitialize;
end;

function TMyThread.Reconnect: Boolean;
begin
  Result:= False;
  if FDB.Connected then
    FDB.Connected:= False;
  FDB.ConnectionString:= FConnectionString;
  try
    FDB.Connected:= True; //How to abort?
    Result:= True;
  except
    on e: exception do begin
      //MessageDlg(e.Message, mtError, [mbOK], 0);
      FDB.Connected:= False;
      Result:= False;
    end;
  end;
end;

procedure TMyThread.Process;
begin
  if Reconnect then begin //Once connected, keep alive in loop
    while FActive do begin
      if Terminated then Break;
      if not Connected then Break;

      //Do Some Database Work

    end;
  end else begin
    //Log connection failure
  end;
end;

procedure TMyThread.Execute;
begin
  while not Terminated do begin
    if FActive then begin
      Init; //CoInitialize, create DB, etc.
      try
        while (FActive) and (not Terminated) do begin
          try
            Process; //Actual processing procedure
          except
            on e: exception do begin
              //Record error to log
            end;
          end;
        end;
      finally
        Uninit; //CoUninitialize, destroy DB, etc.
      end;
    end;
  end;
end;

(Tried to include just relevant things to the question)

Upvotes: 3

Views: 2541

Answers (1)

NGLN
NGLN

Reputation: 43659

First thing that comes to mind is to reduce connection's timeout. Why do you not want that? And why do you want to establish a connection when closing the application? Especially when you prefer to abort it when it takes more time than expected, why connect at all? Sounds like we could know more background info.

In the special case that you really need it on the condition that it connects quickly, ánd when this issue only applies to application's destruction, then I suggest not to wait for the thread to finish. Just do not free it, terminate the application, and let Windows kill the process including all its threads.

In the case that the connection does succeed, then this approach could backfire, so signal your main thread when the thread dóes connect, and postpone its termination by yet waiting for the thread. You may need another timeout for that again.

Edit:

I suppose the OnWillConnect event will occur every time the attempt to connect is made. Try returning EventStatus := esCancel within its handler.

Upvotes: 2

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