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

   1 package org.opendaylight.controller.md.sal.common.impl.util;
   2
   3 import java.util.concurrent.locks.Lock;
   4 import java.util.concurrent.locks.ReadWriteLock;
   5 import java.util.concurrent.locks.ReentrantLock;
   6 import java.util.concurrent.locks.ReentrantReadWriteLock;
   7 import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
   8 import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;
   9
  10 import org.opendaylight.yangtools.concepts.Delegator;
  11
  12 import com.google.common.base.Preconditions;
  13
  14 public class AbstractLockableDelegator<T> implements Delegator<T> {
  15
  16     private final ReentrantReadWriteLock delegateLock = new ReentrantReadWriteLock();
  17     private final ReadLock delegateReadLock = delegateLock.readLock();
  18     private final WriteLock delegateWriteLock = delegateLock.writeLock();
  19
  20
  21     protected Lock getDelegateReadLock() {
  22         return delegateReadLock;
  23     }
  24
  25     private T delegate;
  26
  27     public AbstractLockableDelegator() {
  28         // NOOP
  29     }
  30
  31     public AbstractLockableDelegator(T initialDelegate) {
  32         delegate = initialDelegate;
  33     }
  34
  35     @Override
  36     public T getDelegate() {
  37         try {
  38             delegateReadLock.lock();
  39             return delegate;
  40         } finally {
  41             delegateReadLock.unlock();
  42         }
  43     }
  44
  45     public T retrieveDelegate() {
  46         try {
  47             delegateReadLock.lock();
  48             Preconditions.checkState(delegate != null,"Delegate is null");
  49             return delegate;
  50         } finally {
  51             delegateReadLock.unlock();
  52         }
  53     }
  54
  55     /**
  56      *
  57      * @param newDelegate
  58      * @return oldDelegate
  59      */
  60     public final T changeDelegate(T newDelegate) {
  61         try {
  62             delegateWriteLock.lock();
  63             T oldDelegate = delegate;
  64             delegate = newDelegate;
  65             onDelegateChanged(oldDelegate, newDelegate);
  66             return oldDelegate;
  67         } finally {
  68             delegateWriteLock.unlock();
  69         }
  70     }
  71
  72
  73     protected void onDelegateChanged(T oldDelegate, T newDelegate) {
  74         // NOOP in abstract calss;
  75     }
  76 }