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.activemq.transport.amqp.client;
  
  import java.nio.charset.StandardCharsets;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.Set;
  
  /**
   * Utility class that can generate and if enabled pool the binary tag values used to identify transfers over an AMQP
   * link.
   */
  public final class AmqpTransferTagGenerator {
  
     public static final int DEFAULT_TAG_POOL_SIZE = 1024;
  
     private long nextTagId;
     private int maxPoolSize = DEFAULT_TAG_POOL_SIZE;
  
     private final Set<byte[]> tagPool;
  
     public AmqpTransferTagGenerator() {
        this(false);
     }
  
     public AmqpTransferTagGenerator(boolean pool) {
        if (pool) {
           this.tagPool = new LinkedHashSet<>();
        } else {
           this.tagPool = null;
        }
     }
  
     /**
      * Retrieves the next available tag.
      *
      * @return a new or unused tag depending on the pool option
      */
     public byte[] getNextTag() {
        byte[] rc;
        if (tagPool != null && !tagPool.isEmpty()) {
           final Iterator<byte[]> iterator = tagPool.iterator();
           rc = iterator.next();
           iterator.remove();
        } else {
           rc = Long.toHexString(nextTagId++).getBytes(StandardCharsets.UTF_8);
        }
        return rc;
     }
  
     /**
      * When used as a pooled cache of tags the unused tags should always be returned once the transfer has been settled.
      *
      * @param data a previously borrowed tag that is no longer in use.
      */
     public void returnTag(byte[] data) {
        if (tagPool != null && tagPool.size() < maxPoolSize) {
           tagPool.add(data);
        }
     }
  
     /**
      * Gets the current max pool size value.
      *
      * @return the current max tag pool size
      */
     public int getMaxPoolSize() {
        return maxPoolSize;
     }
  
     /**
      * Sets the max tag pool size.  If the size is smaller than the current number of pooled tags the pool will drain
      * over time until it matches the max.
      *
      * @param maxPoolSize the maximum number of tags to hold in the pool.
      */
     public void setMaxPoolSize(int maxPoolSize) {
        this.maxPoolSize = maxPoolSize;
     }
  }
  