《Java ConcurrentHashMap 源码：线程安全的底层逻辑》（968）
# 《Java ConcurrentHashMap 源码：线程安全的底层逻辑》🔍
在Java并发编程中，`ConcurrentHashMap`是线程安全哈希表的典范实现🌟。它通过精妙的设计避免了全局锁的性能瓶颈，让我们深入探究其底层逻辑。
## 分段锁设计 🧩
JDK7采用**分段锁(Segment)**机制，将整个Map分成16个Segment，每个Segment独立加锁🔒。这种设计允许多线程同时操作不同Segment，大幅提升并发性能🚀。
## CAS与synchronized优化 ⚡
JDK8进行了革命性改进：
1. 抛弃分段锁，改用**Node+CAS+synchronized**组合拳
2. 首次插入时使用CAS保证原子性
3. 哈希冲突时对链表头节点加synchronized锁
```java
// JDK8 putVal方法核心逻辑
if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null, new Node<K,V>(hash, key, value)))
break; // CAS成功插入新节点
}
```
## 扩容机制 📈
采用**多线程协同扩容**策略：
- 维护`transferIndex`指针记录扩容进度
- 线程可以协助迁移其他桶的数据
- 扩容期间查询操作无需阻塞
## 迭代器弱一致性 🔄
`ConcurrentHashMap`的迭代器具有**弱一致性**特点：
- 不保证反映所有最新修改
- 但保证不会抛出`ConcurrentModificationException`
这种设计在并发性能与数据一致性间取得了精妙平衡⚖️，是Java并发容器中的经典之作🎯。
5G.okatady141.asia/PoSt/1125_581669.HtM
5G.okatady140.asia/PoSt/1125_044958.HtM
5G.okatady139.asia/PoSt/1125_845433.HtM
5G.okatady138.asia/PoSt/1125_612328.HtM
5G.okatady137.asia/PoSt/1125_838602.HtM
5G.okatady136.asia/PoSt/1125_667312.HtM
5G.okatady135.asia/PoSt/1125_560185.HtM
5G.okatady134.asia/PoSt/1125_378955.HtM
5G.okatady133.asia/PoSt/1125_524390.HtM
5G.okatady132.asia/PoSt/1125_221581.HtM
5G.okatady141.asia/PoSt/1125_559345.HtM
5G.okatady140.asia/PoSt/1125_816079.HtM
5G.okatady139.asia/PoSt/1125_339518.HtM
5G.okatady138.asia/PoSt/1125_453874.HtM
5G.okatady137.asia/PoSt/1125_350084.HtM
5G.okatady136.asia/PoSt/1125_778907.HtM
5G.okatady135.asia/PoSt/1125_615676.HtM
5G.okatady134.asia/PoSt/1125_607599.HtM
5G.okatady133.asia/PoSt/1125_864274.HtM
5G.okatady132.asia/PoSt/1125_904825.HtM
5G.okatady141.asia/PoSt/1125_261011.HtM
5G.okatady140.asia/PoSt/1125_791898.HtM
5G.okatady139.asia/PoSt/1125_957240.HtM
5G.okatady138.asia/PoSt/1125_651261.HtM
5G.okatady137.asia/PoSt/1125_120273.HtM
5G.okatady136.asia/PoSt/1125_362456.HtM
5G.okatady135.asia/PoSt/1125_865426.HtM
5G.okatady134.asia/PoSt/1125_541012.HtM
5G.okatady133.asia/PoSt/1125_012018.HtM
5G.okatady132.asia/PoSt/1125_297417.HtM
5G.okatady141.asia/PoSt/1125_562015.HtM
5G.okatady140.asia/PoSt/1125_071633.HtM
5G.okatady139.asia/PoSt/1125_595453.HtM
5G.okatady138.asia/PoSt/1125_751958.HtM
5G.okatady137.asia/PoSt/1125_618757.HtM
5G.okatady136.asia/PoSt/1125_552745.HtM
5G.okatady135.asia/PoSt/1125_515285.HtM
5G.okatady134.asia/PoSt/1125_042026.HtM
5G.okatady133.asia/PoSt/1125_410247.HtM
5G.okatady132.asia/PoSt/1125_207500.HtM
5G.okatady141.asia/PoSt/1125_858368.HtM
5G.okatady140.asia/PoSt/1125_645834.HtM
5G.okatady139.asia/PoSt/1125_661760.HtM
5G.okatady138.asia/PoSt/1125_643809.HtM
5G.okatady137.asia/PoSt/1125_187525.HtM
5G.okatady136.asia/PoSt/1125_223142.HtM
5G.okatady135.asia/PoSt/1125_475578.HtM
5G.okatady134.asia/PoSt/1125_156901.HtM
5G.okatady133.asia/PoSt/1125_725739.HtM
5G.okatady132.asia/PoSt/1125_407157.HtM
5G.okatady141.asia/PoSt/1125_766188.HtM
5G.okatady140.asia/PoSt/1125_233858.HtM
5G.okatady139.asia/PoSt/1125_216982.HtM
5G.okatady138.asia/PoSt/1125_445961.HtM
5G.okatady137.asia/PoSt/1125_053038.HtM
5G.okatady136.asia/PoSt/1125_510886.HtM
5G.okatady135.asia/PoSt/1125_103236.HtM
5G.okatady134.asia/PoSt/1125_177255.HtM
5G.okatady133.asia/PoSt/1125_271073.HtM
5G.okatady132.asia/PoSt/1125_660306.HtM
5G.okatady131.asia/PoSt/1125_016932.HtM
5G.okatady130.asia/PoSt/1125_040042.HtM
5G.okatady129.asia/PoSt/1125_156941.HtM
5G.okatady128.asia/PoSt/1125_467561.HtM
5G.okatady127.asia/PoSt/1125_664908.HtM
5G.okatady126.asia/PoSt/1125_827763.HtM
5G.okatady125.asia/PoSt/1125_590981.HtM
5G.okatady124.asia/PoSt/1125_993862.HtM
5G.okatady123.asia/PoSt/1125_267199.HtM
5G.okatady122.asia/PoSt/1125_710483.HtM
5G.okatady131.asia/PoSt/1125_927928.HtM
5G.okatady130.asia/PoSt/1125_077274.HtM
5G.okatady129.asia/PoSt/1125_151448.HtM
5G.okatady128.asia/PoSt/1125_968966.HtM
5G.okatady127.asia/PoSt/1125_982970.HtM
5G.okatady126.asia/PoSt/1125_882019.HtM
5G.okatady125.asia/PoSt/1125_791309.HtM
5G.okatady124.asia/PoSt/1125_433683.HtM
5G.okatady123.asia/PoSt/1125_048367.HtM
5G.okatady122.asia/PoSt/1125_655868.HtM
查看15道真题和解析