为 NavigableMap 编写同步的线程安全包装器

Writing a synchronized thread-safety wrapper for NavigableMap(为 NavigableMap 编写同步的线程安全包装器)

问题描述

java.util.Collections 目前提供以下实用方法来为各种集合接口创建 synchronized 包装器:

• synchronizedCollection(Collection<T>c)
• synchronizedList(Listlist)
• synchronizedMap(Mapm)
• synchronizedSet(Sets)
• synchronizedSortedMap(SortedMapm)
• synchronizedSortedSet(SortedSets)

类似地，它也有 6 个 unmodifiedXXX 重载.

Analogously, it also has 6 unmodifiedXXX overloads.

这里明显的遗漏是 的实用方法NavigableMap.extends SortedMap 确实如此，但 SortedSet extends Set 和 Set extends Collection 和 Collections 也有SortedSet 和 Set 的专用实用方法.大概 NavigableMap 是一个有用的抽象，否则它一开始就不会存在，但它没有实用方法.

The glaring omission here are the utility methods for NavigableMap<K,V>. It's true that it extends SortedMap, but so does SortedSet extends Set, and Set extends Collection, and Collections have dedicated utility methods for SortedSet and Set. Presumably NavigableMap is a useful abstraction, or else it wouldn't have been there in the first place, and yet there are no utility methods for it.

所以问题是:

• Collections 没有为 NavigableMap 提供实用方法有什么具体原因吗?
• 您将如何为 NavigableMap 编写自己的 synchronized 包装器?
  • 浏览 Collections.java 的 OpenJDK 版本的源代码似乎表明这只是一个机械"过程
    • 是不是一般可以像这样添加synchronized线程安全特性?
    • 如果是这样一个机械过程，能否实现自动化?(Eclipse 插件等)
    • 这种代码重复是必要的，还是可以通过不同的 OOP 设计模式避免?
    • Is there a specific reason why Collections doesn't provide utility methods for NavigableMap?
    • How would you write your own synchronized wrapper for NavigableMap?
      • Glancing at the source code for OpenJDK version of Collections.java seems to suggest that this is just a "mechanical" process
        • Is it true that in general you can add synchronized thread-safetiness feature like this?
        • If it's such a mechanical process, can it be automated? (Eclipse plug-in, etc)
        • Is this code repetition necessary, or could it have been avoided by a different OOP design pattern?

        推荐答案

        这是一个疏忽.修复正在进行中.

        乔希写道:

        他们绝对属于那里.他们的缺席是无意的.
        我们应该尽快把它们放进去."

        "They definitely belong there. Their absence is unintentional.
        We should put them in as soon as possible."

        我同意，尽管我们没有一个工程师期待编写(和测试)所有那些令人麻木的转发方法.发布日期:2006-08-21 00:50:41.0

        I agree, even though none of us engineers are looking forward to writing (and testing) all those mind-numbing forwarding methods. Posted Date : 2006-08-21 00:50:41.0

        这需要一些时间.

        更新:至于手动实现，你可以考虑劫持java.util包，因为你想扩展static class SynchronizedSortedMap 被声明为包私有.否则它将是大量的代码复制粘贴.下面是开场白:

        Update: as to manually implementing it, you may consider to hijack the java.util package since you would like to extend static class SynchronizedSortedMap<K, V> which is declared package private. Else it's going to be a lot of code copypaste. Here's a kickoff:

        package java.util;
        
        import java.util.Collections.SynchronizedSortedMap;
        
        public class NewCollections {
        
            public static <K, V> NavigableMap<K, V> synchronizedNavigableMap(NavigableMap<K, V> m) {
                return new SynchronizedNavigableMap<K, V>(m);
            }
        
            static class SynchronizedNavigableMap<K, V> extends SynchronizedSortedMap<K, V> implements NavigableMap<K, V> {
                private final NavigableMap<K, V> sm;
        
                SynchronizedNavigableMap(NavigableMap<K, V> m) {
                    super(m);
                    sm = m;
                }
        
                SynchronizedNavigableMap(NavigableMap<K, V> m, Object mutex) {
                    super(m, mutex);
                    sm = m;
                }
        
            }
        }
        

        让 IDE 自动生成 NavigableMap 的未实现方法，并以与 SynchronizedSortedMap 相同的方式对它们进行编码.这是一个例子:

        Let the IDE autogenerate the unimplemented methods of NavigableMap and code them the same way as SynchronizedSortedMap does. Here's ONE example:

                @Override
                public K ceilingKey(K key) {
                    synchronized (mutex) { return sm.ceilingKey(key); }
                }
        

        请注意，返回例如 Set 的方法您也需要将其包装在 SynchronizedSet 中.再次，请参阅 SynchronizedMap 和 SynchronizedSortedMap 来源以获得见解:)

        Note that the methods which returns for example Set you'll need to wrap it in SynchronizedSet as well. Again, see the SynchronizedMap and SynchronizedSortedMap sources for insights :)

        我不认为它(能够)是一个机械过程，因为它涉及很多因素.

        I don't expect it to be (able to be) a mechanical process since it involves a lot of factors.

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