创建我自己的自定义线程池执行器

Question

我在创建自己的自定义线程池执行器时遇到了一个问题。我正在尝试在不使用任何执行器服务库的情况下实现相同的目的，以便为 java 面试做准备。我可以在下面的服务中编写代码。

import java.util.LinkedList;
import java.util.Queue;

class Worker extends Thread {
    private final Queue<Runnable> taskQueue;
    private volatile boolean isStopped = false;

    public Worker(Queue<Runnable> taskQueue) {
        this.taskQueue = taskQueue;
    }

    public void run() {
        while (!isStopped) {
            Runnable task = null;
            synchronized (taskQueue) {
                while (taskQueue.isEmpty() && !isStopped) {
                    try {
                        taskQueue.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                if (!taskQueue.isEmpty()) {
                    task = taskQueue.poll();
                }
            }
            if (task != null) {
                task.run();
            }
            if(isStopped)
            return;
        }
    }

    public void stopThread() {
        isStopped = true;
        interrupt(); // Interrupt the thread if it's waiting
    }
}

public class CustomThreadPool {
    private final int poolSize;
    private final Queue<Runnable> taskQueue;
    private final Worker[] workers;

    public CustomThreadPool(int poolSize) {
        this.poolSize = poolSize;
        taskQueue = new LinkedList<>();
        workers = new Worker[poolSize];
        for (int i = 0; i < poolSize; i++) {
            workers[i] = new Worker(taskQueue);
            workers[i].start();
        }
    }

    public void execute(Runnable task) {
        synchronized (taskQueue) {
            taskQueue.offer(task);
            taskQueue.notifyAll(); // Notify all waiting threads to start executing the task
        }
    }

    public void shutdown() {
        for (Worker worker : workers) {
            worker.stopThread();
        }
    }

    public static void main(String[] args) {
        CustomThreadPool threadPool = new CustomThreadPool(3);

        // Submit tasks to the thread pool
        for (int i = 1; i <= 5; i++) {
            int num = i;
            threadPool.execute(() -> {
                int result = calculateFactorial(num);
                System.out.println("Factorial of " + num + " is " + result + " - Thread: " + Thread.currentThread().getName());
            });
        }

        // Shutdown the thread pool
        threadPool.shutdown();
    }

    private static int calculateFactorial(int n) {
        int factorial = 1;
        for (int i = 1; i <= n; i++) {
            factorial *= i;
        }
        return factorial;
    }
}

下面是上面代码的输出。

Factorial of 1 is 1 - Thread: Thread-0
Factorial of 2 is 2 - Thread: Thread-1
Factorial of 3 is 6 - Thread: Thread-2

这里的问题是我向执行器提交了 5 个任务，我也可以在任务队列中看到相同的任务，但只有 3/5 任务正在执行，因为线程池大小保持为 3。我希望这 3 个线程以某种方式运行这 5 个任务。我需要帮助来理解我做错了什么以及如何强制相同的 3 个线程执行队列中的所有预配任务。

Answer 1

threadPool.shutdown()

调用会杀死所有正在运行的线程，即使它们有待处理的工作。

尝试这样做：

将以下方法添加到您的 CustomThreadPool 中：

    public void join() throws InterruptedException {
        for (Worker worker : workers) {
            worker.join();
        }
    }

然后，而不是

threadPool.shutdown();

使用

        try {
            threadPool.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

join()

将等待所有工作线程完成其任务然后返回。