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ShowMessage in Service halts process

Posted on 2009-03-29
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Last Modified: 2013-11-22
I created a service (i.e. runs as a service, not an application).  I found afterwards it was calling a piece of code which had a showmessage contained in it.  Consequently it was halting continuation.

Short of ensuring my code does not contain any showmessages, are there any alternatives?  A lot of this code is used in win applications.


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Question by:markschenkel
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by:pmunro
pmunro earned 25 total points
ID: 24014479
If you set the service to not interact with the desktop, this should stop the messages popping up and pausing the services running.
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by:btframework
btframework earned 25 total points
ID: 24014727
By default windows NT (4.0, 2000, XP, Vista) has "two" desktops. One is for user and other one is system. You may see the system desktop before login.
So any service in the system by default uses system desktop. You should switch it to user desktop before showing any messages, dialogs or something like that.
Any way, take a look at this please: http://articles.techrepublic.com.com/5100-10878_11-1050538.html
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Assisted Solution

by:Geert Gruwez
Geert Gruwez earned 75 total points
ID: 24018951
create a unit with a ShowMessage procedure/function which you let it call Dialogs when in an ordinary app or logs the message to file when in a service application


unit AppMessenger;
 

interface
 

implementation
 

uses Dialogs, SvcMgr;
 

const

  ServiceAppName = 'ServiceApp';
 

  fServiceApp: integer = 0;

  fEventLogger: TEventLogger = nil;
 

function IsServiceApp: boolean;

begin

  if fServiceApp = 0 then

  begin

    if Assigned(SvcMgr.Application) then

    begin

      fServiceApp := 2;

      fEventLogger := TEventLogger.Create(ServiceAppName);

    end else

      FServiceApp := 1;

  end;

  Result := fServiceApp = 2;

end;
 

procedure ShowMessage(const Msg: string);

begin

  if IsServiceApp then

    fEventLogger.LogMessage(Msg)

  else

    Dialogs.ShowMessage(Msg);

end;
 

end.

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markschenkel earned 0 total points
ID: 24032214
<<If you set the service to not interact with the desktop, this should stop the messages popping up and pausing the services running.>>
I experimented with this setting.  When it is unchecked the service simply hangs (I guess it is probably displaying a message on the desktop btframework alludes to).  But when checked it displays the showmessage on the desktop (and of course halts the app).

I have seen similar like solutions to Geert_Gruwez.  What I was hoping for was a solution which would detect any showmessages at compile time.  Is it possible to detect if ShowMessage is compiled??? (assuming if it is not used the optimizer removes it)

Ultimately I guess this rests with cautious/careful coding practices.  
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LVL 37

Expert Comment

by:Geert Gruwez
ID: 24036745
it will allways be compiled when you use the dialogs unit
the trick is to fool delphi to use your own unit by placing it last in the uses list
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