JCTools, 場景特化的併發類庫，某些程度上能夠提高性能

同上一篇同樣，在jmap -histo中發現MpscChunkedArrayQueue類的實例比較多，javadoc看了下，其原來是出自JC Tools，https://github.com/JCTools/JCTools。

經過官網，咱們能夠看到，它針對實際的場景對JDK自帶的併發隊列作了一些特定的優化，以下：

Java Concurrency Tools for the JVM. This project aims to offer some concurrent data structures currently missing from the JDK:

• SPSC/MPSC/SPMC/MPMC variations for concurrent queues:

  • SPSC - Single Producer Single Consumer (Wait Free, bounded and unbounded)
  • MPSC - Multi Producer Single Consumer (Lock less, bounded and unbounded)
  • SPMC - Single Producer Multi Consumer (Lock less, bounded)
  • MPMC - Multi Producer Multi Consumer (Lock less, bounded)

• SPSC/MPSC linked array queues offer a balance between performance, allocation and footprint

• An expanded queue interface (MessagePassingQueue):

  • relaxedOffer/Peek/Poll: trade off conflated guarantee on full/empty queue state with improved performance.
  • drain/fill: batch read and write methods for increased throughput and reduced contention

不過總體瀏覽了下，文檔較少，benchmark提供了用例但沒有看到結果，真用到的時候，能夠看下到底性能能夠提高多少。有一文章對源碼進行了分析（http://blog.csdn.net/youaremoon/article/details/50351929），不過說實話，不知道如今爲何不少人喜歡share源碼分析，僅僅只是源碼分析，對場景化的適用條件以及原理和實現機制卻是考慮的不多。舉個例子，https://www.qcloud.com/community/article/904925001482373849?utm_source=Community&utm_medium=article904925001482373849&utm_campaign=kyzg就是一篇典型的文章，是爲了說明看過源碼了、仍是理解了。一般，我的認爲理解如何實現、適用場景及優缺點是同等重要的，不然就只顧趕路、卻不關心本身在哪裏了。