add heartbeat, not tested yet.

lichao

2021-04-09 4e5cb7960ce4e7e66d5190be67426aeca8b55c3d

 src/msg.cpp

@@ -78,6 +78,14 @@
   return true;
}

bool MsgI::EnableRefCount(SharedMemory &shm)
{
   if (!IsCounted()) {
      count_ = shm.New<RefCount>();
   }
   return IsCounted();
}

int MsgI::Release(SharedMemory &shm)
{
   if (IsCounted()) {