Github user ahgittin commented on a diff in the pull request:

    https://github.com/apache/brooklyn-server/pull/340#discussion_r80078720
  
    --- Diff: 
core/src/main/java/org/apache/brooklyn/core/config/internal/LazyContainerAndKeyValue.java
 ---
    @@ -0,0 +1,93 @@
    +/*
    + * 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.
    + */
    +package org.apache.brooklyn.core.config.internal;
    +
    +import javax.annotation.Nullable;
    +
    +import org.apache.brooklyn.config.ConfigKey;
    +import org.apache.brooklyn.config.ConfigValueAtContainer;
    +import org.apache.brooklyn.util.guava.Maybe;
    +
    +import com.google.common.base.Function;
    +import com.google.common.base.Preconditions;
    +
    +public class LazyContainerAndKeyValue<TContainer,TValue> implements 
ConfigValueAtContainer<TContainer,TValue> {
    +    
    +    @Nullable private final TContainer container;
    +    @Nullable private final ConfigKey<TValue> key;
    +    private final Function<TContainer,Maybe<Object>> 
lookupResolutionFunction;
    +    private final Function<Maybe<Object>,Maybe<TValue>> conversionFunction;
    +    private Maybe<TValue> resolved;
    +    
    +    public LazyContainerAndKeyValue(@Nullable ConfigKey<TValue> key, 
@Nullable TContainer container, 
    +            Function<TContainer, Maybe<Object>> lookupResolutionFunction,
    +            Function<Maybe<Object>, Maybe<TValue>> conversionFunction) {
    +        this.key = key;
    +        this.container = container;
    +        this.lookupResolutionFunction = 
Preconditions.checkNotNull(lookupResolutionFunction);
    +        this.conversionFunction = 
Preconditions.checkNotNull(conversionFunction);
    +    }
    +
    +    protected synchronized Maybe<TValue> resolve() {
    +        if (resolved==null) { 
    +            resolved = conversionFunction.apply(
    --- End diff --
    
    no one else should synchronize on this so pretty sure it's fine, though i 
take your point


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