如何返回已完成线程的结果列表？ThreadUnion实现问题排查

• 现有线程分解程序，除results()方法外其余测试均通过，目前仅能收集抛出异常的线程结果，无法统计正常完成的线程。
• 测试失败报错：

org.opentest4j.AssertionFailedError:
Expected :7
Actual :4

核心方法要求 #

1. Thread newThread(Runnable runnable)：创建并注册线程，命名规则为[name]-worker-n，需监控线程执行全过程
2. List results()：返回已完成线程的结果列表，每条结果需包含线程名、结束时间戳、异常（若有）

当前实现代码 #

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

public class ThreadUnionImpl implements ThreadUnion{

    private final String name;
    private final AtomicInteger threadCount = new AtomicInteger(0);
    private final List<FinishedThreadResult> threadList = Collections.synchronizedList(new ArrayList<>());
    private boolean shutdownRequested = false;
    public ThreadUnionImpl(String name) {
        this.name = name;
    }
    @Override
    public int totalSize() {
        return threadCount.get();
    }

    @Override
    public int activeSize() {
        return (int)Thread.getAllStackTraces().keySet().stream()
                .filter(thread -> thread.getName().startsWith(name + "-worker-"))
                .count();
    }

    @Override
    public void shutdown() {
        shutdownRequested = true;
        Thread.getAllStackTraces().keySet().stream()
                .filter(thread -> thread.getName().startsWith(name + "-worker-"))
                .forEach(Thread::interrupt);
        Thread.getAllStackTraces().keySet().stream()
                .filter(thread -> thread.getName().startsWith(name + "-worker-"))
                .forEach(Thread::interrupt);
    }

    @Override
    public boolean isShutdown() {
        return shutdownRequested;
    }

    @Override
    public void awaitTermination() {
        Thread.getAllStackTraces().keySet().stream()
                .filter(thread -> thread.getName().startsWith(name + "-worker-"))
                .forEach(thread -> {
                    try {
                        thread.join();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                });
    }

    @Override
    public boolean isFinished() {
        return shutdownRequested && activeSize() == 0;
    }

    @Override
    public List<FinishedThreadResult> results() {
        return threadList;
    }

    @Override
    public Thread newThread(Runnable r) {
        if (shutdownRequested) throw new IllegalStateException();
        String threadName = this.name + "-worker-" + threadCount.getAndIncrement();
        Thread thread = new Thread(r, threadName);
        thread.setUncaughtExceptionHandler((t, e) -> {
            threadList.add(new FinishedThreadResult(t.getName(), e));
        });
        return thread;
    }
}

问题分析与解决方案 #

当前代码仅通过UncaughtExceptionHandler捕获异常线程的结果，正常完成的线程不会触发该处理器，导致results()返回的结果数量不足。需要用catch-finally包装传入的Runnable，确保无论线程正常结束还是抛出异常，都能将结果写入列表。

修改newThread方法如下：

@Override
public Thread newThread(Runnable r) {
    if (shutdownRequested) throw new IllegalStateException();
    String threadName = this.name + "-worker-" + threadCount.getAndIncrement();
    // 包装原始Runnable，添加监控逻辑
    Runnable wrappedRunnable = () -> {
        Exception exception = null;
        long endTime = 0L;
        try {
            r.run(); // 执行原始任务
        } catch (Exception e) {
            exception = e; // 捕获异常
        } finally {
            endTime = System.currentTimeMillis(); // 记录结束时间戳
            // 将结果加入列表，无论是否异常
            threadList.add(new FinishedThreadResult(threadName, endTime, exception));
        }
    };
    Thread thread = new Thread(wrappedRunnable, threadName);
    // 保留UncaughtExceptionHandler作为兜底，防止未捕获的Error等
    thread.setUncaughtExceptionHandler((t, e) -> {
        long endTime = System.currentTimeMillis();
        threadList.add(new FinishedThreadResult(t.getName(), endTime, new RuntimeException(e)));
    });
    return thread;
}

关键修改点 #

1. 对传入的Runnable进行包装，在try块执行原始任务，catch捕获所有异常，finally块中统一记录结束时间并添加结果到列表
2. 保留UncaughtExceptionHandler作为兜底，处理Error等未被catch捕获的严重异常
3. 确保FinishedThreadResult构造方法支持接收线程名、结束时间戳、异常三个参数（需根据实际定义调整）

这样修改后，正常完成的线程和异常线程的结果都会被收集，results()返回的数量就能匹配预期值。

内容的提问来源于stack exchange，提问作者Kere