geode-core/src/main/java/org/apache/geode/internal/tcp/MsgIdGenerator.java

/*
 * 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.geode.internal.tcp;

import org.apache.geode.annotations.internal.MakeNotStatic;
import org.apache.geode.internal.UniqueIdGenerator;

/**
 * MsgId is used to generate unique ids to attach to messages. To get a new id call obtain. When you
 * are done with the id call release. Failure to call release will eventually cause obtain to fail
 * with an exception.
 * <p>
 * Currently ids are in the range 0..32767 inclusive.
 *
 * @since GemFire 5.0.2
 *
 */
public class MsgIdGenerator {
  /**
   * A value that can be used to indicate that a message does not have an id.
   */
  public static final short NO_MSG_ID = -1;
  private static final short MAX_ID = 32767;
  @MakeNotStatic("Possibly safe singleton to share?")
  private static final UniqueIdGenerator uigen = new UniqueIdGenerator(MAX_ID);

  private MsgIdGenerator() {
    // static only; no constructor
  }

  /**
   * Obtains a message id. Callers of this must call release when finished with the id.
   *
   * @throws IllegalStateException if all ids have been obtained
   */
  public static short obtain() {
    return (short) uigen.obtain();
  }

  public static void release(short id) {
    if (id != NO_MSG_ID) {
      uigen.release(id);
    }
  }
}