Synchronized与ReentrantReadWriteLock性能比较

     在J道看多线程的文章，看到有人说Synchronized与ReentrantReadWriteLock比，性能不如ReentrantReadWriteLock，Synchronized读取数据不加锁，会造成读的时候还未写入，加锁会造成读互斥，不能并发访问，从而影响性能。为此做了一个测试。

     1:Synchronized不加读琐

/** * */ package com.thread; import java.util.ArrayList; import java.util.List; import java.util.concurrent.locks.ReentrantReadWriteLock; /** * 比较synchronized和ReentrantReadWriteLock的性能 * @author Administrator * */ public class SynchronizedAndReentrantReadWriteLock { // 时间记录器 private long timeRecord = System.currentTimeMillis(); /** * @param args */ public static void main(String[] args) { A a = new SynchronizedAndReentrantReadWriteLock().new A(); //B b = new SynchronizedAndReentrantReadWriteLock().new B(); List<A> aaList = new ArrayList<A>(1000); for (int i = 0; i < 1000; i++) { A aa = new SynchronizedAndReentrantReadWriteLock().new A(); aa.setState(-1); aaList.add(aa); } //Thread t1 = new Thread(new SynchronizedAndReentrantReadWriteLock().new Thread1(aaList, null)); //读 Thread t2 = new Thread(new SynchronizedAndReentrantReadWriteLock().new Thread2(aaList, null)); //写 List<Thread> tt = new ArrayList<Thread>(); for (int i = 0; i < 10; i++) { Thread t1 = new Thread(new SynchronizedAndReentrantReadWriteLock().new Thread1(aaList, null)); tt.add(t1); } //long start = System.currentTimeMillis(); //System.out.println("start" + start); //t2.setPriority(Thread.MAX_PRIORITY); for (int i = 0; i < tt.size(); i++) { Thread te = tt.get(i); te.start(); } t2.start(); //System.out.println("end" + (System.currentTimeMillis() - start)); } // synchronized class A { private int state; public synchronized void setState(int a) { this.state = a; } public int getState() { return this.state; } } // ReentrantReadWriteLock class B { private int state; ReentrantReadWriteLock.ReadLock read = new ReentrantReadWriteLock().readLock(); ReentrantReadWriteLock.WriteLock write = new ReentrantReadWriteLock().writeLock(); public void setState(int a) { write.lock(); try { this.state = a; } finally { write.unlock(); } } public int getState() { read.lock(); try { return this.state; } finally { read.unlock(); } } } // read线程 class Thread1 implements Runnable { private A objA; private List<A> objaList; private B objB; public void run() { if (null != objaList) { for (int i = 0; i < objaList.size(); i++) { A aa = objaList.get(i); System.out.println("读线程--" + i + "--:" + aa.getState()); try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } if(i == objaList.size()-1) { long end = System.currentTimeMillis(); System.out.println("读线程耗时：" + (end - timeRecord)); } } } } public A getObjA() { return objA; } public void setObjA(A objA) { this.objA = objA; } public B getObjB() { return objB; } public void setObjB(B objB) { this.objB = objB; } public Thread1(List<A> objaList, B objB) { super(); this.objaList = objaList; this.objB = objB; } public List<A> getObjaList() { return objaList; } public void setObjaList(List<A> objaList) { this.objaList = objaList; } } // write线程 class Thread2 implements Runnable { private A objA; private List<A> objaList; private B objB; public void run() { if (null != objaList) { for (int i = 0; i < objaList.size(); i++) { A aa = objaList.get(i); aa.setState(i+1); System.out.println("写线程--" + i + "--:" + (i+1)); try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } } } } public A getObjA() { return objA; } public void setObjA(A objA) { this.objA = objA; } public B getObjB() { return objB; } public void setObjB(B objB) { this.objB = objB; } public Thread2(List<A> objaList, B objB) { super(); this.objaList = objaList; this.objB = objB; } public List<A> getObjaList() { return objaList; } public void setObjaList(List<A> objaList) { this.objaList = objaList; } } }

控制台输出，结果显示，不加读琐，会有线程读的数据不一致的情况

读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 读线程--0--:-1 写线程--0--:1 读线程--0--:1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 读线程--1--:-1 写线程--1--:2 读线程--1--:2 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 读线程--2--:-1 写线程--2--:3 读线程--2--:3 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:-1 读线程--3--:4 写线程--3--:4 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:-1 读线程--4--:5 写线程--4--:5

 

     2:Synchronized加读琐，耗时15828,ReentrantReadWriteLock加读琐16641   (5000个线程,1W线程ReentrantReadWriteLock跑不起来)

     ReentrantReadWriteLock:1093  Synchronized:1092 (200个线程)

再分别测试了其他情况，发现只有当线程数达到一定数量级，使用ReentrantReadWriteLock才会体现高性能。