JCTools简介-白红宇

JCTools简介

阅读量：5865 次

发布时间：2019-06-19

本文共 2297 字，大约阅读时间需要 7 分钟。

序

JCTools是一款对jdk并发数据结构进行增强的并发工具，主要提供了map以及queue的增强数据结构。原来netty还是自己写的MpscLinkedQueueNode，后来新版本就换成使用JCTools的并发队列了。

增强map

ConcurrentAutoTable(后面几个map/set结构的基础)

NonBlockingHashMap

NonBlockingHashMapLong

NonBlockingHashSet

NonBlockingIdentityHashMap

NonBlockingSetInt

增强队列

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)

maven


                
     
      org.jctools
                 
     
      jctools-core
                 
     
      2.1.0

ConcurrentAutoTable

替代AtomicLong，专门为高性能的counter设计的。只有几个方法

public void add( long x );public void decrement();public void increment();public void set( long x );public long get();public int  intValue();public long longValue();public long estimate_get();

对比AtomicLong主要是操作之后没有立即返回

public final long incrementAndGet();public final long decrementAndGet()

NonBlockingHashMap

NonBlockingHashMap是对ConcurrentHashMap的增强，对多CPU的支持以及高并发更新提供更好的性能。

NonBlockingHashMapLong是key为Long型的NonBlockingHashMap。

NonBlockingHashSet是对NonBlockingHashMap的简单包装以支持set的接口。

NonBlockingIdentityHashMap是从NonBlockingHashMap改造来的，使用System.identityHashCode()来计算哈希

NonBlockingSetInt是一个使用CAS的简单的bit-vector

原来是

// --- hash ----------------------------------------------------------------  // Helper function to spread lousy hashCodes.  Throws NPE for null Key, on  // purpose - as the first place to conveniently toss the required NPE for a  // null Key.  private static final int hash(final Object key) {    int h = key.hashCode();     // The real hashCode call    h ^= (h>>>20) ^ (h>>>12);    h ^= (h>>> 7) ^ (h>>> 4);    h += h<<7; // smear low bits up high, for hashcodes that only differ by 1    return h;  }

改为

// --- hash ----------------------------------------------------------------  // Helper function to spread lousy hashCodes  private static final int hash(final Object key) {    int h = System.identityHashCode(key); // The real hashCode call    // I assume that System.identityHashCode is well implemented with a good    // spreader, and a second bit-spreader is redundant.    //h ^= (h>>>20) ^ (h>>>12);    //h ^= (h>>> 7) ^ (h>>> 4);    return h;  }