對於Synchronized、ReentrantLock、Atomic、CAS在併發下面的效能比較測試
對於Synchronized、ReentrantLock、Atomic、CAS在併發下面的效能比較，在JDK1.6和JDK1.8下面測試通過。
我們考慮一個最簡單的併發場景，對物件自增欄位在併發下面的處理：
介面：Counter
public interface Counter {
void increment();
long getCounter();
}
執行執行緒：CounterThread
public class CounterThread implements Runnable{
private Counter counter;
private int num;
public CounterThread(Counter counter , int num){
this.counter = counter;
this.num = num;
}
@Override
public void run() {
// TODO Auto-generated method stub
for(int i=0;i<num;i++){
counter.increment();
}
}
}
不考慮執行緒安全的前提下，設計的普通子類：NormalCounter
/**
* @author chenmeiyang
* 普通版本
*/
public class NormalCounter implements Counter{
private long num = 0;
@Override
public void increment() {
// TODO Auto-generated method stub
num++;
}
@Override
public long getCounter() {
// TODO Auto-generated method stub
return num;
}
}
主程式入口：ConcurrencyTest
public class ConcurrencyTest {
public static void main(String[] args)throws Exception{
int threads = 1000;//執行緒數
int increments = 100000;
//Counter c = new ReentrantLockCounter();
Counter c = new NormalCounter();
//Counter c = new SynchronizedCounter();
//Counter c = new AtomicCounter();
ExecutorService pool = Executors.newFixedThreadPool( threads );
long start = System.currentTimeMillis();
for(int i=0;i<threads;i++){
pool.submit(new CounterThread(c , increments));
}
pool.shutdown();
pool.awaitTermination(1, TimeUnit.MINUTES);
System.out.println("=====執行緒池是否已經停止執行："+pool.isTerminated());
System.out.println("===========總共耗時："+(System.currentTimeMillis()-start));
System.out.println("======最終值為："+c.getCounter());
}
}
執行結果：（執行緒不安全，資料不正確）
=====執行緒池是否已經停止執行：true
===========總共耗時：858
======最終值為：94046638
=====執行緒池是否已經停止執行：true
===========總共耗時：751
======最終值為：96394997
=====執行緒池是否已經停止執行：true
===========總共耗時：889
======最終值為：95764624
=====執行緒池是否已經停止執行：true
===========總共耗時：920
======最終值為：97167161
用jdk自帶的關鍵字synchroized加鎖處理：SynchronizedCounter
public class SynchronizedCounter implements Counter {
private long num = 0;
@Override
public synchronized void increment() {
// TODO Auto-generated method stub
num++;
}
@Override
public long getCounter() {
// TODO Auto-generated method stub
return num;
}
}
synchronized執行結果：(執行緒安全，保證了資料的正確性，但是耗時較長)
=====執行緒池是否已經停止執行：true
===========總共耗時：4625
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：4952
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：4558
======最終值為：100000000
下面，用ReentrantLock鎖處理：ReentrantLockCounter
public class ReentrantLockCounter implements Counter{
private long counter = 0;
private ReentrantLock lock = new ReentrantLock();
@Override
public void increment() {
// TODO Auto-generated method stub
try{
lock.lock();
counter++;
}catch(Exception e){
e.printStackTrace();
}finally{
lock.unlock();
}
}
@Override
public long getCounter() {
// TODO Auto-generated method stub
return this.counter;
}
}
執行結果：（執行緒安全，資料正確，而且耗時比synchronized短）
=====執行緒池是否已經停止執行：true
===========總共耗時：3073
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：3058
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：3044
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：3075
======最終值為：100000000
下面，用Atomic試試：AtomicCounter
public class AtomicCounter implements Counter{
private AtomicLong num = new AtomicLong(0);
@Override
public void increment() {
// TODO Auto-generated method stub
num.incrementAndGet();
}
@Override
public long getCounter() {
// TODO Auto-generated method stub
return num.get();
}
}
執行結果，（執行緒安全，資料正確，耗時比ReentrantLock還短）
=====執行緒池是否已經停止執行：true
===========總共耗時：2636
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：2449
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：2558
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：2543
======最終值為：100000000
最後，我們再試下CAS：
public class CASCounter implements Counter{
private volatile long num = 0;
private Unsafe unsafe;
private long offset;
public CASCounter() throws Exception {
unsafe = this.getUnsafe();
offset = unsafe.objectFieldOffset(CASCounter.class.getDeclaredField("num"));
}
private Unsafe getUnsafe()throws Exception{
Field f = Unsafe.class.getDeclaredField("theUnsafe");
f.setAccessible(true);
Unsafe unsafe = (Unsafe) f.get(null);
return unsafe;
}
@Override
public void increment() {
// TODO Auto-generated method stub
long before = num;
while (!unsafe.compareAndSwapLong(this, offset, before, before + 1)) {
before = num;
}
}
@Override
public long getCounter() {
// TODO Auto-generated method stub
return num;
}
}
執行結果：（執行緒安全，資料正確，但是耗時很長）
=====執行緒池是否已經停止執行：true
===========總共耗時：8505
======最終值為：100000000
=====執行緒池是否已經停止執行：true
===========總共耗時：9003
======最終值為：100000000