countDownLatch和cyclicBarrier
《 Effecit In Java 》说过,从java 1.5发现版本开始, 就不建议使用wait和notify,它们使用比较困难,可以使用更高级并发工具来替代。
图一所说的同步器是指那些能使线程等待另一个线程的对象,常用的有cyclicBarrier和倒计数锁存器CountDownLatch和semaphore。
CountDownLatch
一个同步辅助类,在完成一组正在其他线程中执行的操作之前,它允许一个或多个线程一直等待。它的倒计数类似于AutomicInteger的getAndDecrement()。但它还有另一个主要作用类似于 wait和notify。
代码示例:
package com.bbk.u001.handle;
import java.util.concurrent.CountDownLatch;
import javax.annotation.PostConstruct;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;
/**
* CountDownLatch的使用
* @ClassName: StatsSimilarKnowledgeHandle
* @Description: TODO
* @author wasim
* @create at 2015-8-12 下午8:44:51
*
*/
@Component
public class CountDownLatchHandle {
@Autowired
ThreadPoolTaskExecutor executor;
@PostConstruct
public void handleStatsQuestionKnowledge(){
CountDownLatch startSignal = new CountDownLatch(12);
//导出文件
executor.execute(new ExportStats(startSignal));
//导出文件前,需要先循环下面12个线程
for(int i=0;i<12;i++){
executor.execute(new similarKnowledgeHandle(startSignal));
}
}
public class similarKnowledgeHandle implements Runnable{
CountDownLatch startSignal;
public similarKnowledgeHandle(CountDownLatch startSignal) {
this.startSignal =startSignal;
}
@Override
public void run() {
startSignal.countDown();
System.out.println(startSignal.getCount()); //显示当前计数
}
}
public class ExportStats implements Runnable{
CountDownLatch startSignal;
public ExportStats(CountDownLatch startSignal) {
this.startSignal =startSignal;
}
@Override
public void run() {
try {
startSignal.await(); //当计数为0前,导出文件的线程一直处于等待状态
System.out.println("start export.......");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
cyclicBarrier
一个同步辅助类,它允许一组线程互相等待,直到到达某个公共屏障点 (common barrier point)。在涉及一组固定大小的线程的程序中,这些线程必须不时地互相等待,此时 CyclicBarrier 很有用。因为该 barrier 在释放等待线程后可以重用,所以称它为循环 的 barrier。
代码示例:
class Solver {
final int N;
final float[][] data;
final CyclicBarrier barrier;
class Worker implements Runnable {
int myRow;
Worker(int row) { myRow = row; }
public void run() {
while (!done()) {
processRow(myRow);
try {
barrier.await();
} catch (InterruptedException ex) {
return;
} catch (BrokenBarrierException ex) {
return;
}
}
}
}
public Solver(float[][] matrix) {
data = matrix;
N = matrix.length;
barrier = new CyclicBarrier(N,
new Runnable() {
public void run() {
mergeRows(...);
}
});
for (int i = 0; i < N; ++i)
new Thread(new Worker(i)).start();
waitUntilDone();
}
}
cyclicBarrier 和 CountDownLatch 的区别
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