heartbeat threads blocks process shutdown because its hashed-wheel-timer is non-daemon thread.
* The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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 */
package org.apache.dubbo.remoting.exchange.support.header;
import org.apache.dubbo.common.Constants;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.timer.HashedWheelTimer;
import org.apache.dubbo.remoting.ChannelHandler;
import org.apache.dubbo.remoting.Client;
import org.apache.dubbo.remoting.RemotingException;
import org.apache.dubbo.remoting.exchange.ExchangeChannel;
import org.apache.dubbo.remoting.exchange.ExchangeClient;
import org.apache.dubbo.remoting.exchange.ExchangeHandler;
import org.apache.dubbo.remoting.exchange.ResponseFuture;
import java.net.InetSocketAddress;
import java.util.Collections;
import java.util.concurrent.TimeUnit;
/**
 * DefaultMessageClient
 */
public class HeaderExchangeClient implements ExchangeClient {