@Override
    public boolean handleMessage(Message message) {
        boolean handled = true;
        Object removed = null;
        Object key = null;
        switch (message.what) {
            case ID_REMOVE_FRAGMENT_MANAGER:
                android.app.FragmentManager fm = (android.app.FragmentManager) message.obj;
                key = fm;
                removed = pendingRequestManagerFragments.remove(fm);
                break;
            case ID_REMOVE_SUPPORT_FRAGMENT_MANAGER:
                FragmentManager supportFm = (FragmentManager) message.obj;
                key = supportFm;
                removed = pendingSupportRequestManagerFragments.remove(supportFm);
                break;
            default:
                handled = false;
        }
        if (handled && removed == null && Log.isLoggable(TAG, Log.WARN)) {
            Log.w(TAG, "Failed to remove expected request manager fragment, manager: " + key);
        }
        return handled;
    }
Retrieves and returns the RequestManagerRetriever singleton.
core/src/main/java/com/bumptech/glide/manager/RequestManagerRetriever.java