Callable接口以及CyclicBarrier实现list数据求和

public class CountListIntegerWithCallable {
public static void main(String[] args) {
int threadNum = 10;

ExecutorService executorService = Executors.newFixedThreadPool(threadNum);
List<Integer> list = new LinkedList<Integer>();
for (int i = 0; i <100; ++i) {
list.add(i);
}
int len = list.size() / threadNum;
if (0 == len) {
threadNum = list.size();
len = 1;
}

List<Callable<Long>> callableList = new LinkedList<Callable<Long>>();

for (int i = 0; i < threadNum; ++i) {
List<Integer> subList = new LinkedList<Integer>();
if (i == threadNum - 1) {//最后一个线程处理剩下所有任务
subList = list.subList(i * len, list.size());
} else {
subList = list.subList(i * len, (i + 1) * len);
}
final List<Integer> finalSubList = subList;
callableList.add(new Callable<Long>() {
public Long call() throws Exception {
long sum = 0;
for (int j = 0; j < finalSubList.size(); j++) {
sum += finalSubList.get(j);
}
System.out.println("分配给线程："+Thread.currentThread().getName()+" list元素部分计数和为："+sum);
return sum;
}
});
}

try {
//            这个不用自己控制等待，invokeAll执行给定的任务，当所有任务完成时，返回保持任务状态和结果的 Future 列表
List<Future<Long>> futureList = executorService.invokeAll(callableList);
for (Future<Long> future : futureList) {
System.out.println(future.get());
}
} catch (InterruptedException e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
} catch (Exception e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
}

}
}

public class CountSumWithCyclicBarrier {
private CyclicBarrier cyclicBarrier;
private long totalSum;

private long getSum() {
int threadNum = 10;
ExecutorService executorService = Executors.newFixedThreadPool(threadNum);
List<Integer> list = new LinkedList<Integer>();
for (int i = 0; i < 100; ++i) {
list.add(i);
}
int len = list.size() / threadNum;
if (0 == len) {
threadNum = list.size();
len = 1;
}
cyclicBarrier = new CyclicBarrier(threadNum + 1);
List<Integer> subList = new LinkedList<Integer>();
for (int i = 0; i < threadNum; ++i) {
if (i == threadNum - 1) {//最后一个线程处理剩余list中数据
subList = list.subList(i * len, list.size());
} else {
subList = list.subList(i * len, (i + 1) * len);
}
executorService.submit(new TaskDemo(subList, i));

}
try {
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
} catch (BrokenBarrierException e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
}
return totalSum;

}

public static void main(String[] args) {
CountSumWithCyclicBarrier countSumWithCyclicBarrier = new CountSumWithCyclicBarrier();
System.out.print(countSumWithCyclicBarrier.getSum());
}

class TaskDemo implements Runnable {
private List<Integer> subList;
private int i;

public TaskDemo(List<Integer> subList, int i) {
this.subList = subList;
this.i = i;
}

public void run() {
long sum = 0;
for (int j = 0; j < subList.size(); ++j) {
sum += subList.get(j);
}

System.out.println("分配给线程：" + i + " " + Thread.currentThread().getName() + "那一部分List的整数和为Sum:" + sum);
synchronized (TaskDemo.class) {
totalSum += sum;
}
//线程间相互等待，只有所有线程执行完后，才进行下面操作

try {
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
} catch (BrokenBarrierException e) {
e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
}

}
}
}

cyclicBarrier = new CyclicBarrier(threadNum + 1);

threadNum+1 加1会阻塞主线程

countDownLatch和CyclicBarrier区别：

countDownLatch是一个线程，等待其他几个线程完，才继续执行下面代码，例如多人赛跑

CyclicBarrier与CountDownLatch类似，但是可以去完成好几个阶段的任务，比如上述三个人约好去地点A吃饭，到店吃玩饭后继续出发，到下一个目的地，全部到了之后再吃饭。

此时CyclicBarrier可以完成循环等待。

//3个人出发，每个人到店之后报告老板
CyclicBarrier cb =new CyclicBarrier(3);
for(...){
//每个人出发
go(cb);
}

//一个人的行程
go(CyclicBarrier cb){
//到达地点1，等待其他人到齐
cb.await();
//都到了吃饭，然后再出发
eat then <a target=_blank href="http://www.cxyclub.cn/Tag/continue.html" target="_blank" style="outline-style: none; color: rgb(76, 120, 153);">continue</a> going;

//到达地点2，等待其他人到齐
cb.await();
//都到了吃饭
eat;
}