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
<dependency>
<groupId>org.jctools</groupId>
<artifactId>jctools-core</artifactId>
<version>2.1.0</version>
</dependency>
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;
}
