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.ReentrantReadWriteLock;
  12 import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
  13 import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;
  14
  15 import org.opendaylight.yangtools.concepts.Delegator;
  16
  17 import com.google.common.base.Preconditions;
  18
  19 public class AbstractLockableDelegator<T> implements Delegator<T> {
  20
  21     private final ReentrantReadWriteLock delegateLock = new ReentrantReadWriteLock();
  22     private final ReadLock delegateReadLock = delegateLock.readLock();
  23     private final WriteLock delegateWriteLock = delegateLock.writeLock();
  24
  25
  26     protected Lock getDelegateReadLock() {
  27         return delegateReadLock;
  28     }
  29
  30     private T delegate;
  31
  32     public AbstractLockableDelegator() {
  33         // NOOP
  34     }
  35
  36     public AbstractLockableDelegator(T initialDelegate) {
  37         delegate = initialDelegate;
  38     }
  39
  40     @Override
  41     public T getDelegate() {
  42         try {
  43             delegateReadLock.lock();
  44             return delegate;
  45         } finally {
  46             delegateReadLock.unlock();
  47         }
  48     }
  49
  50     public T retrieveDelegate() {
  51         try {
  52             delegateReadLock.lock();
  53             Preconditions.checkState(delegate != null,"Delegate is null");
  54             return delegate;
  55         } finally {
  56             delegateReadLock.unlock();
  57         }
  58     }
  59
  60     /**
  61      *
  62      * @param newDelegate
  63      * @return oldDelegate
  64      */
  65     public final T changeDelegate(T newDelegate) {
  66         try {
  67             delegateWriteLock.lock();
  68             T oldDelegate = delegate;
  69             delegate = newDelegate;
  70             onDelegateChanged(oldDelegate, newDelegate);
  71             return oldDelegate;
  72         } finally {
  73             delegateWriteLock.unlock();
  74         }
  75     }
  76
  77
  78     protected void onDelegateChanged(T oldDelegate, T newDelegate) {
  79         // NOOP in abstract calss;
  80     }
  81 }