How to stop the thread created in CImageDecoder?

Dear All,

In my app, I used the CImageDecoder to decode a bmp file with the EOptionAlwaysThread parameter to call the member function Convert() of  CImageDecoder  class. After finish the decoding, the app cannot be terminated exactly.

The following is my code fragment:

class CImageHandler : public CActive
{
public:
   static CImageHandler* NewL(RFs& fs);
  ~CImageHandler();

private:
   CImageHandler(RFs& fs);
   
public:
   // It is the caller's responsobility to delete the return pointer
   CFbsBitmap* LoadFileL(const TDesC& aFilename);

private:
   // Active object interface
   void RunL();
   void DoCancel();

private:
   CImageDecoder* iLoadUtil;
   RFs&           iFs;          
   
};

//////////////////////////
CImageHandler* CImageHandler::NewL(RFs& fs)
{
  CImageHandler* p=new (ELeave) CImageHandler(fs);
  CActiveScheduler::Add(p);
  return p;
}

CImageHandler::CImageHandler(RFs& fs) :
CActive(CActive::EPriorityStandard), iFs(fs)
{
}

CImageHandler::~CImageHandler()
{
   Cancel();
   Deque();
  delete iLoadUtil;
   
}


//the decoder function
CFbsBitmap* CImageHandler::LoadFileL(const TDesC& aFilename)
{
   ASSERT(!IsActive());
   if(IsActive())
       return NULL;

   delete iLoadUtil;
   iLoadUtil = NULL;
   iLoadUtil = CImageDecoder::FileNewL(iFs, aFilename,
                    CImageDecoder::EOptionAlwaysThread);            
   
   // Bitmap
   CFbsBitmap* pBitmap = new CFbsBitmap();
   if(pBitmap)
   {
        //some line to create the CFbsBitmap
        ......
        iLoadUtil->Convert(&iStatus, *pBitmap, 0);
       SetActive();
       User::WaitForRequest(iStatus);
       if(iStatus.Int() != KErrNone)
      {
          delete pBitmap;
          pBitmap = NULL;
       }
               
     }

    return pBitmap;
}


void CImageHandler::RunL()
{

}
   
void CImageHandler::DoCancel()
{
   // Cancel everything possible
   if(iLoadUtil)
       iLoadUtil->Cancel();
}

/////////////////////////////////////////////

I use the User::WaitForRequest(iStatus) function to wait the thread decode the file synchronously.
The app can run in success, but cannot exit.
I had done my best but I still failed to find the reason. Pleas help me.

Thanks in advance.