java并发初探ConcurrentSkipListMap

ConcurrentSkipListMap以调表这种数据结构以空间换时间获得效率，通过volatile和CAS操作保证线程安全，而且它保证了有序性，比TreeMap比线程安全。

跳表结构

通过level down right可以更快插入和查找元素

     ** 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* +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+  +-+

例子

package com.java.javabase.thread.collection;import lombok.extern.slf4j.Slf4j;import java.security.SecureRandom;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentSkipListMap;/*** @author*/
@Slf4j
public class ConcurrentSkipMapTest {//public static TreeMap<String, Integer> map = new TreeMap();public static ConcurrentSkipListMap<String, Integer> map = new ConcurrentSkipListMap<>();public static int size = 10;public static void main(String[] args) {InnerThread t1 =new InnerThread("t1");InnerThread t2 =new InnerThread("t2");t1.start();t2.start();try {Thread.sleep(1000);printMap(map);} catch (InterruptedException e) {e.printStackTrace();}}static class InnerThread extends Thread {String name;public InnerThread(String name) {super(name);this.name=name;}@Overridepublic void run() {Random random = new Random(System.currentTimeMillis());for (int i = 0; i < size; i++) {String key =String.valueOf(random.nextInt(1000))+name;//Wlog.info(key);map.put(key, Integer.valueOf(i));printMapNone(map);}}}public static void printMap(Map<String, Integer> map) {//Iterator<Map.Entry<K,V>> i = entrySet().iterator();Iterator<Map.Entry<String, Integer>> it = map.entrySet().iterator();while (it.hasNext()) {Map.Entry<String, Integer> entry = it.next();String key = entry.getKey();Integer value = entry.getValue();log.info("key {} value {}", key, value);}}public static void printMapNone(Map<String, Integer> map) {//Iterator<Map.Entry<K,V>> i = entrySet().iterator();Iterator<Map.Entry<String, Integer>> it = map.entrySet().iterator();while (it.hasNext()) {Map.Entry<String, Integer> entry = it.next();String key = entry.getKey();Integer value = entry.getValue();}}
}

run result

019-08-28 19:34:31,919   [main] INFO  ConcurrentSkipMapTest  - key 101t1 value 5
2019-08-28 19:34:31,921   [main] INFO  ConcurrentSkipMapTest  - key 101t2 value 5
2019-08-28 19:34:31,921   [main] INFO  ConcurrentSkipMapTest  - key 131t1 value 7
2019-08-28 19:34:31,921   [main] INFO  ConcurrentSkipMapTest  - key 131t2 value 7
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 180t1 value 3
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 180t2 value 3
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 209t1 value 9
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 209t2 value 9
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 349t1 value 6
2019-08-28 19:34:31,922   [main] INFO  ConcurrentSkipMapTest  - key 349t2 value 6
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 527t1 value 4
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 527t2 value 4
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 655t1 value 1
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 655t2 value 1
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 714t1 value 8
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 714t2 value 8
2019-08-28 19:34:31,923   [main] INFO  ConcurrentSkipMapTest  - key 781t1 value 2
2019-08-28 19:34:31,924   [main] INFO  ConcurrentSkipMapTest  - key 781t2 value 2
2019-08-28 19:34:31,924   [main] INFO  ConcurrentSkipMapTest  - key 797t1 value 0
2019-08-28 19:34:31,924   [main] INFO  ConcurrentSkipMapTest  - key 797t2 value 0