// for tracking the idle time state
 BOOL bIdle = TRUE;
 LONG lIdleCount = 0;

 // acquire and dispatch messages until a WM_QUIT message is received.
 for (;;)
 {
  // phase1: check to see if we can do idle work
  while (bIdle &&
   !::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE))
  {
   // call OnIdle while in bIdle state
   if (!OnIdle(lIdleCount++))
    bIdle = FALSE; // assume "no idle" state
  }

  // phase2: pump messages while available
  do
  {
   // pump message, but quit on WM_QUIT
   if (!PumpMessage())
    return ExitInstance();

   // reset "no idle" state after pumping "normal" message
   if (IsIdleMessage(&m_msgCur))
   {
    bIdle = TRUE;
    lIdleCount = 0;
   }

  } while (::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE));
 }

 ASSERT(FALSE);  // not reachable
}

BOOL CWinThread::IsIdleMessage(MSG* pMsg)
{
 // Return FALSE if the message just dispatched should _not_
 // cause OnIdle to be run.  Messages which do not usually
 // affect the state of the user interface and happen very
 // often are checked for.

 // redundant WM_MOUSEMOVE and WM_NCMOUSEMOVE
 if (pMsg->message == WM_MOUSEMOVE || pMsg->message == WM_NCMOUSEMOVE)
 {
  // mouse move at same position as last mouse move?
  if (m_ptCursorLast == pMsg->pt && pMsg->message == m_nMsgLast)
   return FALSE;

  m_ptCursorLast = pMsg->pt;  // remember for next time
  m_nMsgLast = pMsg->message;
  return TRUE;
 }

 // WM_PAINT and WM_SYSTIMER (caret blink)
 return pMsg->message != WM_PAINT && pMsg->message != 0x0118;
}
这是SDI处理消息的中心机构，但请注意，它觉对不是核心！
分析一下，在无限循环FOR内部又出现一个WHILE循环
while (bIdle &&
   !::PeekMessage(&m_msgCur, NULL, NULL, NULL, PM_NOREMOVE))
  {
   // call OnIdle while in bIdle state
   if (!OnIdle(lIdleCount++))
    bIdle = FALSE; // assume "no idle" state
  }
这段代码是当你程序进程的消息队列中没有消息时，会调用OnIdle做一些后备工作，
临时对象在这里被删除。当然它是虚函数。其中的PeekMessage，是查看消息队列，如果有消息返回TRUE，如果没有消息返回FALSE，这里指定PM_NOREMOVE，是指查看过后不移走消息队列中刚刚被查看到的消息，也就是说这里的PeekMessage只起到一个检测作用，显然返回FALSE时［即没有消息］，才会进入循环内部，执行OnIdle，当然了，你的OnIdle返回FLASE，会让程序不再执行OnIdle。你可能要问