为什么jdk中没有ConcurrentLinkedHashMap类？ [英] Why there is no ConcurrentLinkedHashMap class in jdk?

问题描述

此问题直接从我之前的这个问题在这里。我认为我的第二个问题的答案是否定的。所以我想了解为什么java.util.concurrent包中没有ConcurrentLinkedHashMap？我的意思是有一个ConcurrentHashMap，但没有ConcurrentLinkedHashMap。在并发环境中有这样一个课程是否没有任何意义？我的意思是这里的主要技术原因是不可用的？在Guava / Apache Commons中有类似的东西吗？

This question follows directly from my previous question here in SO . I think the answer to my second question is no . So I would like understand why there is no ConcurrentLinkedHashMap in java.util.concurrent package ? I mean there is a ConcurrentHashMap but no ConcurrentLinkedHashMap . Does it not make any sense at all to have such a class in Concurrent environments ? I mean what is the main technical reason here for its non availabalility ? Is there something similar in Guava/ Apache Commons ?

推荐答案

为什么jdk中没有ConcurrentLinkedHashMap类？

Why there is no ConcurrentLinkedHashMap class in jdk?

你需要问Oracle Java的人，但我想象它是一个组合：

You would need to ask the Oracle Java guys that, but I imagine it it is a combination of:

• 一种认为没有多少人需要它的感觉，而


• 在高度并发的用例中实现具有良好性能的数据结构的固有困难。
  

• a perception that not many people would need it, and
• the inherent difficulties in implementing data structures with good performance properties in highly concurrent use cases.

在这种情况下，在我看来，实现集合类，以便迭代键/值/条目集不是一个并发的瓶颈。 ..嗯...很难（即使人们想要做到这一点，事实仍然是，设计和实现和证明通用高度并发的数据结构和算法的正确性很困难。）

In this case, it seems to me that implementing the collection class so that iterating the key/value/entry sets is not a concurrency bottleneck would be ... um ... difficult. (And even if people have figured a way to do it, the fact remains that designing and implementing and proving the correctness of general purpose highly concurrent data structures and algorithms is hard.)

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