content: /*
   *  Licensed 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.
   *
   *  See the NOTICE file distributed with this work for additional
   *  information regarding copyright ownership.
   */
  
  package org.seaborne.delta.server.system;
  
  import java.util.ArrayList ;
  import java.util.List ;
  import java.util.ServiceLoader ;
  
  /** Implementation of {@link SubsystemRegistry} for use in the simple 
   *  but common case of running Delta as a collection of jars
   *  on the classpath. 
   *  <p>
   *  Uses {@link ServiceLoader} to find sub-systems. 
   */
  public class SubsystemRegistryBasic<T> implements SubsystemRegistry<T> {
      
      private List<T> registry = new ArrayList<>() ;
      private Object registryLock = new Object() ;
      private Class<T> classAtRuntime; 
  
      public SubsystemRegistryBasic(Class<T> cls) {
          classAtRuntime = cls;
      }
       
      @Override
      public void load() {
          synchronized (registryLock) {
              // Find subsystems asking for initialization. 
              ServiceLoader<T> sl = 
                  // Use this->classloader form : better for OSGi 
                  ServiceLoader.load(classAtRuntime, this.getClass().getClassLoader()) ;
              sl.forEach(this::add) ;
          }
      }
  
      @Override
      public void add(T module) {
          synchronized (registryLock) {
              if ( ! registry.contains(module) )
                  registry.add(module);
          }
      }
  
      @Override
      public boolean isRegistered(T module) {
          synchronized (registryLock) {
              return registry.contains(module);
          }
      }
  
      @Override
      public void remove(T module) {
          synchronized (registryLock) {
              registry.remove(module);
          }
      }
  
      @Override
      public int size() {
          synchronized (registryLock) {
              return registry.size();
          }
      }
  
      @Override
      public boolean isEmpty() {
          synchronized (registryLock) {
              return registry.isEmpty();
          }
      }
      
      @Override
      public List<T> snapshot() {
          synchronized (registryLock) {
              return new ArrayList<>(registry) ;
          }
      }
  }