Re: Virtual function call

From:

diligent.snail@gmail.com

Newsgroups:

comp.lang.c++

Date:

Mon, 21 Jan 2008 14:23:35 -0800 (PST)

Message-ID:

<459ad68b-01c7-4ff6-9117-105fd28743fc@d70g2000hsb.googlegroups.com>

On Jan 21, 10:43 pm, "Erazem Polutnik" <erazem_polut...@hotmail.com>
wrote:

Hello,
i have a strange problem, when calling virtual function, using SDL Thread
library. Here is situation:

CThread::CThread
{
    SDL_CreateThread(RunProc,this);

}

virtual bool CThread::IsRunning()
{
    return false;

}

int SDLCALL CThread::RunProc(void *pParam)
{
    /*delay 100ms*/

   CThread *pt=(CThread *)pParam;
   while (pt->IsRunning()) {
      pt->DoRun();
   }

}

then I make:

class CMyThread : public CThread
{
    virtual bool IsRunning()
    {
        return true;
    }

};

After new CMyThread() I expect to function IsRunning to return true, but it
returns false as in CThread class
If I add 100ms delay everthing is working ok.

Many thanks
Erazem

I think what is happening is the following: pt->IsRunning() will
invoke virtual CMyThread::IsRunning only when CMyThread is fully
constructed (CThread has to be constructed first). But then you are
calling SDL_CreateThread(RunProc,this), which is asynchronous, from
CThread's constructor, and there is longer guarantee of which will
happen before the other; CMyThread's full construction, or RunProc's
execution.

Regards.