ConcurrentHashMap与Hashtable、Collections.synchronizedMap(map)比较
ConcurrentHashMap是对HashMap的高并发实现
压力测试方法：
/* * boolean retrieve : 是否获取，true获取和插入，false只插入 */ public static void pressureTest(final Map<String, Integer> map, int threshold, boolean retrieve) throws InterruptedException { System.out.println("Start pressure testing the map ["+map.getClass()+"] use the threshold ["+threshold+"],retrieve=" + retrieve); long totalTime = 0L; final int MAX_THRESHOLD = 2500000; for(int i = 0; i < 5; i++) { long startTime = System.nanoTime(); ExecutorService executorService = Executors.newFixedThreadPool(threshold); for(int j = 0; j < threshold; j++) { executorService.execute(new Runnable() { @Override public void run() { for(int i = 0; i < MAX_THRESHOLD; i++) { Integer randomNumber = (int) Math.ceil(Math.random() * 600000); if(retrieve) { map.get(String.valueOf(randomNumber)); } map.put(String.valueOf(randomNumber), randomNumber); } } }); } executorService.shutdown(); executorService.awaitTermination(2, TimeUnit.HOURS); long endTime = System.nanoTime(); long period = (endTime - startTime) / 1000000L; System.out.println(threshold * MAX_THRESHOLD + " element insert/retrieved in " + period + " ms."); totalTime += period; } System.out.println("For the map ["+map.getClass()+"] the average time is " + (totalTime/5) + " ms."); }
main方法：
public static void main(String[] args) throws InterruptedException { /* * 比较在多线程中的性能差距 * Start pressure testing the map [class java.util.Hashtable] use the threshold [5],retrieve=false 2500000 element insert/retrieved in 1600 ms. 2500000 element insert/retrieved in 1166 ms. 2500000 element insert/retrieved in 1126 ms. 2500000 element insert/retrieved in 1191 ms. 2500000 element insert/retrieved in 1260 ms. For the map [class java.util.Hashtable] the average time is 1268 ms. Start pressure testing the map [class java.util.Hashtable] use the threshold [5],retrieve=true 2500000 element insert/retrieved in 2411 ms. 2500000 element insert/retrieved in 2412 ms. 2500000 element insert/retrieved in 2450 ms. 2500000 element insert/retrieved in 2393 ms. 2500000 element insert/retrieved in 2470 ms. ----------------------------------- For the map [class java.util.Hashtable] the average time is 2427 ms. Start pressure testing the map [class java.util.Collections$SynchronizedMap] use the threshold [5],retrieve=false 2500000 element insert/retrieved in 1474 ms. 2500000 element insert/retrieved in 1483 ms. 2500000 element insert/retrieved in 1468 ms. 2500000 element insert/retrieved in 1615 ms. 2500000 element insert/retrieved in 1395 ms. For the map [class java.util.Collections$SynchronizedMap] the average time is 1487 ms. Start pressure testing the map [class java.util.Collections$SynchronizedMap] use the threshold [5],retrieve=true 2500000 element insert/retrieved in 2379 ms. 2500000 element insert/retrieved in 2339 ms. 2500000 element insert/retrieved in 2393 ms. 2500000 element insert/retrieved in 2347 ms. 2500000 element insert/retrieved in 2358 ms. For the map [class java.util.Collections$SynchronizedMap] the average time is 2363 ms. ----------------------------------- Start pressure testing the map [class java.util.concurrent.ConcurrentHashMap] use the threshold [5],retrieve=false 2500000 element insert/retrieved in 965 ms. 2500000 element insert/retrieved in 830 ms. 2500000 element insert/retrieved in 660 ms. 2500000 element insert/retrieved in 805 ms. 2500000 element insert/retrieved in 605 ms. For the map [class java.util.concurrent.ConcurrentHashMap] the average time is 773 ms. Start pressure testing the map [class java.util.concurrent.ConcurrentHashMap] use the threshold [5],retrieve=true 2500000 element insert/retrieved in 832 ms. 2500000 element insert/retrieved in 779 ms. 2500000 element insert/retrieved in 674 ms. 2500000 element insert/retrieved in 778 ms. 2500000 element insert/retrieved in 748 ms. For the map [class java.util.concurrent.ConcurrentHashMap] the average time is 762 ms. end... 可以看出ConcurrentHashMap的效率最高 */ pressureTest(new Hashtable<String, Integer>(), 5, false); pressureTest(new Hashtable<String, Integer>(), 5, true); System.err.println("-----------------------------------"); pressureTest(Collections.synchronizedMap(new HashMap<String, Integer>()), 5, false); pressureTest(Collections.synchronizedMap(new HashMap<String, Integer>()), 5, true); System.err.println("-----------------------------------"); pressureTest(new ConcurrentHashMap<String, Integer>(), 5, false); pressureTest(new ConcurrentHashMap<String, Integer>(), 5, true); System.out.println("end..."); /* * 比较在单线程中的性能差距 * Start pressure testing the map [class java.util.Hashtable] use the threshold [1],retrieve=false 2500000 element insert/retrieved in 1522 ms. 2500000 element insert/retrieved in 838 ms. 2500000 element insert/retrieved in 782 ms. 2500000 element insert/retrieved in 844 ms. 2500000 element insert/retrieved in 849 ms. For the map [class java.util.Hashtable] the average time is 967 ms. Start pressure testing the map [class java.util.Hashtable] use the threshold [1],retrieve=true 2500000 element insert/retrieved in 1306 ms. 2500000 element insert/retrieved in 1238 ms. 2500000 element insert/retrieved in 1235 ms. 2500000 element insert/retrieved in 1168 ms. 2500000 element insert/retrieved in 1201 ms. ----------------------------------- For the map [class java.util.Hashtable] the average time is 1229 ms. Start pressure testing the map [class java.util.Collections$SynchronizedMap] use the threshold [1],retrieve=false 2500000 element insert/retrieved in 1189 ms. 2500000 element insert/retrieved in 960 ms. 2500000 element insert/retrieved in 1144 ms. 2500000 element insert/retrieved in 1323 ms. 2500000 element insert/retrieved in 1116 ms. For the map [class java.util.Collections$SynchronizedMap] the average time is 1146 ms. Start pressure testing the map [class java.util.Collections$SynchronizedMap] use the threshold [1],retrieve=true 2500000 element insert/retrieved in 1273 ms. 2500000 element insert/retrieved in 1319 ms. 2500000 element insert/retrieved in 1000 ms. 2500000 element insert/retrieved in 1222 ms. 2500000 element insert/retrieved in 1319 ms. For the map [class java.util.Collections$SynchronizedMap] the average time is 1226 ms.----------------------------------- Start pressure testing the map [class java.util.concurrent.ConcurrentHashMap] use the threshold [1],retrieve=false 2500000 element insert/retrieved in 1030 ms. 2500000 element insert/retrieved in 1028 ms. 2500000 element insert/retrieved in 857 ms. 2500000 element insert/retrieved in 1194 ms. 2500000 element insert/retrieved in 873 ms. For the map [class java.util.concurrent.ConcurrentHashMap] the average time is 996 ms. Start pressure testing the map [class java.util.concurrent.ConcurrentHashMap] use the threshold [1],retrieve=true 2500000 element insert/retrieved in 1292 ms. 2500000 element insert/retrieved in 1126 ms. 2500000 element insert/retrieved in 1249 ms. 2500000 element insert/retrieved in 1176 ms. 2500000 element insert/retrieved in 1310 ms. For the map [class java.util.concurrent.ConcurrentHashMap] the average time is 1230 ms. ----------------------------------- Start pressure testing the map [class java.util.HashMap] use the threshold [1],retrieve=false 2500000 element insert/retrieved in 918 ms. 2500000 element insert/retrieved in 912 ms. 2500000 element insert/retrieved in 1109 ms. 2500000 element insert/retrieved in 884 ms. 2500000 element insert/retrieved in 991 ms. For the map [class java.util.HashMap] the average time is 962 ms. Start pressure testing the map [class java.util.HashMap] use the threshold [1],retrieve=true 2500000 element insert/retrieved in 1066 ms. 2500000 element insert/retrieved in 1327 ms. 2500000 element insert/retrieved in 1103 ms. 2500000 element insert/retrieved in 926 ms. 2500000 element insert/retrieved in 1110 ms. For the map [class java.util.HashMap] the average time is 1106 ms. end... hashMap是现成非安全的，在单线程操作下性能并没有超出太多 */ pressureTest(new Hashtable<String, Integer>(), 1, false); pressureTest(new Hashtable<String, Integer>(), 1, true); System.err.println("-----------------------------------"); pressureTest(Collections.synchronizedMap(new HashMap<String, Integer>()), 1, false); pressureTest(Collections.synchronizedMap(new HashMap<String, Integer>()), 1, true); System.err.println("-----------------------------------"); pressureTest(new ConcurrentHashMap<String, Integer>(), 1, false); pressureTest(new ConcurrentHashMap<String, Integer>(), 1, true); System.err.println("-----------------------------------"); pressureTest(new HashMap<String, Integer>(), 1, false); pressureTest(new HashMap<String, Integer>(), 1, true); System.out.println("end..."); }
