content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * 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
   * limitations under the License.
   */
  package org.apache.kafka.raft;
  
  /**
   * This class is used to serialize inbound requests or responses to outbound requests.
   * It basically just allows us to wrap a blocking queue so that we can have a mocked
   * implementation which does not depend on system time.
   *
   * See {@link org.apache.kafka.raft.internals.BlockingMessageQueue}.
   */
  public interface RaftMessageQueue {
  
      /**
       * Block for the arrival of a new message.
       *
       * @param timeoutMs timeout in milliseconds to wait for a new event
       * @return the event or null if either the timeout was reached or there was
       *     a call to {@link #wakeup()} before any events became available
       */
      RaftMessage poll(long timeoutMs);
  
      /**
       * Add a new message to the queue.
       *
       * @param message the message to deliver
       * @throws IllegalStateException if the queue cannot accept the message
       */
      void add(RaftMessage message);
  
      /**
       * Check whether there are pending messages awaiting delivery.
       *
       * @return if there are no pending messages to deliver
       */
      boolean isEmpty();
  
      /**
       * Wakeup the thread blocking in {@link #poll(long)}. This will cause
       * {@link #poll(long)} to return null if no messages are available.
       */
      void wakeup();
  
  }
  