HashMap和ConcurrentHashMap的并发性能测试

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先看看代码吧，模拟1000个并发，每个测试1000次操作，循环测试10轮。分别测试Put和Get操作

    import java.util.Collections;    import java.util.HashMap;    import java.util.Hashtable;    import java.util.Map;    import java.util.concurrent.ConcurrentHashMap;    public class T {      static final int threads = 1000;      static final int NUMBER = 1000;      public static void main(String[] args) throws Exception {        Map<String, Integer> hashmapSync = Collections            .synchronizedMap(new HashMap<String, Integer>());//同步的hashmap        Map<String, Integer> concurrentHashMap = new ConcurrentHashMap<String, Integer>();        Map<String, Integer> hashtable = new Hashtable<String, Integer>();        long totalA = 0;        long totalB = 0;        long totalC = 0;        for (int i = 0; i <= 10; i++) {          totalA += testPut(hashmapSync);          totalB += testPut(concurrentHashMap);          totalC += testPut(hashtable);        }        System.out.println("Put time HashMapSync=" + totalA + "ms.");        System.out.println("Put time ConcurrentHashMap=" + totalB + "ms.");        System.out.println("Put time Hashtable=" + totalC + "ms.");        totalA = 0;        totalB = 0;        totalC = 0;        for (int i = 0; i <= 10; i++) {          totalA += testGet(hashmapSync);          totalB += testGet(concurrentHashMap);          totalC += testGet(hashtable);        }        System.out.println("Get time HashMapSync=" + totalA + "ms.");        System.out.println("Get time ConcurrentHashMap=" + totalB + "ms.");        System.out.println("Get time Hashtable=" + totalC + "ms.");      }      public static long testPut(Map<String, Integer> map) throws Exception {        long start = System.currentTimeMillis();        for (int i = 0; i < threads; i++) {          new MapPutThread(map).start();        }        while (MapPutThread.counter > 0) {          Thread.sleep(1);        }        return System.currentTimeMillis() - start;      }      public static long testGet(Map<String, Integer> map) throws Exception {        long start = System.currentTimeMillis();        for (int i = 0; i < threads; i++) {          new MapPutThread(map).start();        }        while (MapPutThread.counter > 0) {          Thread.sleep(1);        }        return System.currentTimeMillis() - start;      }    }    class MapPutThread extends Thread {      static int counter = 0;      static Object lock = new Object();      private Map<String, Integer> map;      private String key = this.getId() + "";      MapPutThread(Map<String, Integer> map) {        synchronized (lock) {          counter++;        }        this.map = map;      }      public void run() {        for (int i = 1; i <= T.NUMBER; i++) {          map.put(key, i);        }        synchronized (lock) {          counter--;        }      }    }    class MapGetThread extends Thread {      static int counter = 0;      static Object lock = new Object();      private Map<String, Integer> map;      private String key = this.getId() + "";      MapGetThread(Map<String, Integer> map) {        synchronized (lock) {          counter++;        }        this.map = map;      }      public void run() {        for (int i = 1; i <= T.NUMBER; i++) {          map.get(key);        }        synchronized (lock) {          counter--;        }      }    }

运行结果：
Put time HashMapSync=3966ms.
Put time ConcurrentHashMap=1892ms.
Put time Hashtable=3892ms.
Get time HashMapSync=3812ms.
Get time ConcurrentHashMap=1828ms.
Get time Hashtable=3985ms.

结论：
ConcurrentHashMap的性能比同步的HashMap快一倍左右
同步的HashMap和Hashtable的性能相当

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