主题：淘宝面试题：如何充分利用多核CPU，计算很大的List中所有整数的和

最新推荐文章于 2025-08-07 11:47:41 发布

原创最新推荐文章于 2025-08-07 11:47:41 发布 · 173 阅读

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#面试 #thread

本文介绍了一种使用多线程进行大规模整数列表求和的算法实现。该算法通过将任务分配给多个线程并行处理，最终汇总计算结果。文章详细展示了如何设计线程安全的数据结构和同步机制来确保正确性和效率。

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import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

public class MyWorkThread extends Thread {
	private List<integer> list;
	private int start, end;
	private long value;
	private Result result;

	
	public MyWorkThread(List<integer> list, Integer start, Integer end, Result result) {
		this.list = list;
		this.start = start;
		this.end = end;
		this.result = result;
	}


	private void add(int v) {
		if (Long.MAX_VALUE - v &gt; value) {
			value += v;
		} else {
			result.addSum(value);
			value = v;
		}
	}

	public void run() {
		try {
			for(int i = start; i  list = new ArrayList<integer>();
		for (int i = 0; i  threads = new ArrayList<thread>();
		for (;;) {
			end = start + len;
			if (end &gt; list.size()) end = list.size();
			threads.add(new MyWorkThread(list, start, end, result));
			start = end;
			if (start == list.size()) break;
		}
		result.setCountThread(threads.size());
		
		for (Thread thread : threads) {
			thread.start();
		}
		
		synchronized (result) {
			while(!result.isGameOver()) result.wait();
		}
		System.out.println("和为：" + result.getSum());
	}
}

class Result {
	private BigDecimal sum;
	private int countFinish, countThread;
	
	
	public BigDecimal getSum() {
		return sum;
	}
	
	public void setCountThread(int countThread) {
		assert countThread &gt; 0;
		this.countThread = countThread;
	}
	
	
	private void checkGameOver() {
		if (isGameOver()) notifyAll();
	}
	
	public synchronized boolean isGameOver() {
		return countFinish &gt;= countThread;
	}
	
	public synchronized void addSum(long v) {
		sum = sum == null ? new BigDecimal(v) : sum.add(BigDecimal.valueOf(v));
	}
	
	public synchronized void finishA() {
		countFinish++;
		checkGameOver();
	}
}