opendaylight/md-sal/sal-common-impl/src/main/java/org/opendaylight/controller/md/sal/common/impl/util/AbstractLockableDelegator.java

   1 /*
   2  * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8 package org.opendaylight.controller.md.sal.common.impl.util;
   9
  10 import java.util.concurrent.locks.Lock;
  11 import java.util.concurrent.locks.ReadWriteLock;
  12 import java.util.concurrent.locks.ReentrantLock;
  13 import java.util.concurrent.locks.ReentrantReadWriteLock;
  14 import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
  15 import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;
  16
  17 import org.opendaylight.yangtools.concepts.Delegator;
  18
  19 import com.google.common.base.Preconditions;
  20
  21 public class AbstractLockableDelegator<T> implements Delegator<T> {
  22
  23     private final ReentrantReadWriteLock delegateLock = new ReentrantReadWriteLock();
  24     private final ReadLock delegateReadLock = delegateLock.readLock();
  25     private final WriteLock delegateWriteLock = delegateLock.writeLock();
  26
  27
  28     protected Lock getDelegateReadLock() {
  29         return delegateReadLock;
  30     }
  31
  32     private T delegate;
  33
  34     public AbstractLockableDelegator() {
  35         // NOOP
  36     }
  37
  38     public AbstractLockableDelegator(T initialDelegate) {
  39         delegate = initialDelegate;
  40     }
  41
  42     @Override
  43     public T getDelegate() {
  44         try {
  45             delegateReadLock.lock();
  46             return delegate;
  47         } finally {
  48             delegateReadLock.unlock();
  49         }
  50     }
  51
  52     public T retrieveDelegate() {
  53         try {
  54             delegateReadLock.lock();
  55             Preconditions.checkState(delegate != null,"Delegate is null");
  56             return delegate;
  57         } finally {
  58             delegateReadLock.unlock();
  59         }
  60     }
  61
  62     /**
  63      *
  64      * @param newDelegate
  65      * @return oldDelegate
  66      */
  67     public final T changeDelegate(T newDelegate) {
  68         try {
  69             delegateWriteLock.lock();
  70             T oldDelegate = delegate;
  71             delegate = newDelegate;
  72             onDelegateChanged(oldDelegate, newDelegate);
  73             return oldDelegate;
  74         } finally {
  75             delegateWriteLock.unlock();
  76         }
  77     }
  78
  79
  80     protected void onDelegateChanged(T oldDelegate, T newDelegate) {
  81         // NOOP in abstract calss;
  82     }
  83 }