用多线程实现一个数字的自增长到1000000,分别用无锁模式和锁模式来实现代码.
1.使用ReentrantLock.
package test; import java.util.concurrent.CountDownLatch; import java.util.concurrent.locks.ReentrantLock; public class ThreadWithLock { private static final int THREAD_COUNT=3; private static volatile int value= 0; private static final ReentrantLock lock = new ReentrantLock(); private static final CountDownLatch startSignal = new CountDownLatch(1); private static final CountDownLatch endSignal = new CountDownLatch(1); public static void main(String[] args) throws InterruptedException{ for(int i=0;i<=THREAD_COUNT;i++){ (new Counter()).start(); } //start to record time.
long start = System.nanoTime(); //send the started signal to all threads.
startSignal.countDown(); //wait for anyone to finish the counting.
endSignal.await(); long end = System.nanoTime(); System.out.println(end-start); } static class Counter extends Thread { @Override public void run() { try { startSignal.await(); while(true){ try { lock.lock(); if(value<1000000){ value++; } else { break; } } finally{ lock.unlock(); } } endSignal.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } } } }
使用CAS模式，这其实是一种乐观锁模式，它默认是没有竞争的，如果存在竞争，失败了让代码重试.
package test; import java.util.concurrent.CountDownLatch; import java.util.concurrent.atomic.AtomicInteger; public class ThreadNoLock { private static final int THREAD_COUNT=3; private static final AtomicInteger value= new AtomicInteger(0); private static final CountDownLatch startSignal = new CountDownLatch(1); private static final CountDownLatch endSignal = new CountDownLatch(1); public static void main(String[] args) throws InterruptedException{ for(int i=0;i<THREAD_COUNT;i++){ (new Counter()).start(); } //start to record time.
long start = System.nanoTime(); //send the started signal to all threads.
startSignal.countDown(); //wait for anyone to finish the counting.
endSignal.await(); long end = System.nanoTime(); System.out.println(end-start); } static class Counter extends Thread { @Override public void run() { try { startSignal.await(); int current; while(true){ if((current = value.get()) <1000000){ value.compareAndSet(current, current+1); } else{ break; } } endSignal.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } } } }
把Thread_count分别设置为1000,300,30,3 得到的性能数据如下,我们可以发现无锁模式的效率更高.
