package org.eclipse.aether.named.support;
   
   /*
    * 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.
   */
  
  import org.eclipse.aether.named.NamedLockFactory;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Objects;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * Support class for {@link NamedLockFactory} implementations providing reference counting.
   */
  public abstract class NamedLockFactorySupport
      implements NamedLockFactory
  {
      protected final Logger logger = LoggerFactory.getLogger( getClass() );
  
      private final ConcurrentMap<String, NamedLockHolder> locks;
  
      public NamedLockFactorySupport()
      {
          this.locks = new ConcurrentHashMap<>();
      }
  
      @Override
      public NamedLockSupport getLock( final String name )
      {
          return locks.compute( name, ( k, v ) ->
          {
              if ( v == null )
              {
                  v = new NamedLockHolder( createLock( k ) );
              }
              v.incRef();
              return v;
          } ).namedLock;
      }
  
      @Override
      public void shutdown()
      {
          // override if needed
      }
  
      public void closeLock( final String name )
      {
          locks.compute( name, ( k, v ) ->
          {
              if ( v != null && v.decRef() == 0 )
              {
                  destroyLock( v.namedLock.name() );
                  return null;
              }
              return v;
          } );
      }
  
  
      @Override
      protected void finalize() throws Throwable
      {
          try
          {
              if ( !locks.isEmpty() )
              {
                  // report leak
                  logger.warn( "Lock leak, referenced locks still exist {}", locks );
              }
          }
          finally
          {
              super.finalize();
          }
      }
  
      /**
       * Implementations shall create and return {@link NamedLockSupport} for given {@code name}, this method must never
       * return {@code null}.
      */
     protected abstract NamedLockSupport createLock( final String name );
 
     /**
      * Implementation may override this (empty) method to perform some sort of implementation specific cleanup for
      * given lock name. Invoked when reference count for given name drops to zero and named lock was removed.
      */
     protected void destroyLock( final String name )
     {
         // override if needed
     }
 
     private static final class NamedLockHolder
     {
         private final NamedLockSupport namedLock;
 
         private final AtomicInteger referenceCount;
 
         private NamedLockHolder( final NamedLockSupport namedLock )
         {
             this.namedLock = Objects.requireNonNull( namedLock );
             this.referenceCount = new AtomicInteger( 0 );
         }
 
         private int incRef()
         {
             return referenceCount.incrementAndGet();
         }
 
         private int decRef()
         {
             return referenceCount.decrementAndGet();
         }
 
         @Override
         public String toString()
         {
             return "[refCount=" + referenceCount.get() + ", lock=" + namedLock + "]";
         }
     }
 }