package org.eclipse.aether.synccontext;
   
   /*
    * 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 java.util.Collection;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  import javax.annotation.Priority;
  import javax.inject.Named;
  import javax.inject.Singleton;
  
  import org.eclipse.aether.RepositorySystemSession;
  import org.eclipse.aether.SyncContext;
  import org.eclipse.aether.artifact.Artifact;
  import org.eclipse.aether.impl.SyncContextFactory;
  import org.eclipse.aether.metadata.Metadata;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * A singleton factory to create synchronization contexts using a global lock based on
   * {@link ReentrantReadWriteLock}. Explicit artifacts and metadata passed are ignored.
   * <p>
   * <strong>Note: This component is still considered to be experimental, use with caution!</strong>
   */
  @Named
  @Priority( Integer.MAX_VALUE )
  @Singleton
  public class GlobalSyncContextFactory
      implements SyncContextFactory
  {
      private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
  
      public SyncContext newInstance( RepositorySystemSession session, boolean shared )
      {
          return new GlobalSyncContext( shared ? lock.readLock() : lock.writeLock(), shared );
      }
  
      static class GlobalSyncContext
          implements SyncContext
      {
          private static final Logger LOGGER = LoggerFactory.getLogger( GlobalSyncContext.class );
  
          private final Lock lock;
          private final boolean shared;
          private int lockHoldCount;
  
          private GlobalSyncContext( Lock lock, boolean shared )
          {
              this.lock = lock;
              this.shared = shared;
          }
  
          public void acquire( Collection<? extends Artifact> artifact, Collection<? extends Metadata> metadata )
          {
              LOGGER.trace( "Acquiring global {} lock (currently held: {})",
                            shared ? "read" : "write", lockHoldCount );
              lock.lock();
              lockHoldCount++;
          }
  
          public void close()
          {
              while ( lockHoldCount > 0 )
              {
                  LOGGER.trace( "Releasing global {} lock (currently held: {})",
                                shared ? "read" : "write", lockHoldCount );
                  lock.unlock();
                  lockHoldCount--;
              }
          }
  
      }
  
  }