为什么将ConcurrentNavigableMap实现为跳过列表？

Question

最近我遇到了ConcurrentSkipListMap,这是一个skip list实现ConcurrentNavigableMap.现在我想知道,为什么它被实现为skip list.

是否skip list"标准"实施的同时通航地图？是什么skip list让它变得特别好？

Answer 1

ConcurrentSkipListMap 源代码记录了原因.

采用这种方法有两个原因而不是通常的基于数组的方法

1. 基于数组的实现似乎遇到了更多的复杂性和开销
2. 对于遍历较多的索引列表,我们可以使用更便宜的算法,而不是可以用于基本列表

这是javadoc

 /*
 * This class implements a tree-like two-dimensionally linked skip
 * list in which the index levels are represented in separate
 * nodes from the base nodes holding data.  **There are two reasons
 * for taking this approach instead of the usual array-based**
 * structure: 1) Array based implementations seem to encounter
 * more complexity and overhead 2) We can use cheaper algorithms
 * for the heavily-traversed index lists than can be used for the
 * base lists.  Here's a picture of some of the basics for a
 * possible list with 2 levels of index:
 *
 * Head nodes          Index nodes
 * +-+    right        +-+                      +-+
 * |2|---------------->| |--------------------->| |->null
 * +-+                 +-+                      +-+
 *  | down              |                        |
 *  v                   v                        v
 * +-+            +-+  +-+       +-+            +-+       +-+
 * |1|----------->| |->| |------>| |----------->| |------>| |->null
 * +-+            +-+  +-+       +-+            +-+       +-+
 *  v              |    |         |              |         |
 * Nodes  next     v    v         v              v         v
 * +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+
 * | |->|A|->|B|->|C|->|D|->|E|->|F|->|G|->|H|->|I|->|J|->|K|->null
 * +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+