APC测试小问题

[扬帆886]

DWORD WINAPI WorkThread(PVOID pParam)
{
   HANDLE Event = (HANDLE)pParam;
    for(;;)
    {
    DWORD dwRet = WaitForSingleObjectEx(Event, INFINITE, TRUE);
    if(dwRet == WAIT_OBJECT_0)
    {
      printf("event signed");
      break;
    }
    
    else if(dwRet == WAIT_IO_COMPLETION)
    printf("WAIT_IO_COMPLETION\n");
    }
    return 0;
}

VOID CALLBACK APCProc(DWORD dwParam)
{
   printf("%s", (PVOID)dwParam);
}

void TestAPC(BOOL bFast)
{
   HANDLE QuitEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
  HANDLE hThread = CreateThread(NULL,  0,  WorkThread,  (PVOID)QuitEvent,  0,  NULL);
  Sleep(100); // Wait for WorkThread initialized.
  for( int i=5; i>0; i--)
  {
  char a[20]={0};
  itoa(i,a,10);
  strcat(a,"APC HERE\n");

  QueueUserAPC(APCProc, hThread, (DWORD)(PVOID)a);
  if(!bFast)
  Sleep(1000);     /*bFAST = false   投递一个APC,
                   sleep引起hThread 被调度，执行APC，输出结果1
                  bFAST =true    5次投递APC,一次hThread被调度
                     后APC队列中的5个被执行，输出结果2，
                     我想问的是为  什么不是结果3   */
}
   SetEvent(QuitEvent);
   WaitForSingleObject(hThread, INFINITE);
   CloseHandle(hThread);
}

int main(int argc, char* argv[])
{
   TestAPC(true);
   //TestAPC(false);
   getchar();
   return 0;
}

结果1：
5APC HERE
WAIT_IO_COMPLETION
4APC HERE
WAIT_IO_COMPLETION
3APC HERE
WAIT_IO_COMPLETION
2APC HERE
WAIT_IO_COMPLETION
1APC HERE
WAIT_IO_COMPLETION
event signed

结果2：
1APC HERE
1APC HERE
1APC HERE
1APC HERE
1APC HERE
WAIT_IO_COMPLETION
event signed

结果3：
5APC HERE
4APC HERE
3APC HERE
2APC HERE
1APC HERE
WAIT_IO_COMPLETION
event signed