自定义线程池

1、自定义拒绝策略接口

package com.tk.threadPool;


/**
 * 拒绝策略
 *
 * @author taoke
 * @date 2023/3/23
 */
@FunctionalInterface
public interface RejectPolicy<T> {
    /**
     * 拒绝策略规则
     *
     * @param queue 阻塞队列
     * @param task  任务
     */
    void reject(BlockingQueue<T> queue, T task);
}

2、自定义任务队列

package com.tk.threadPool;

import lombok.extern.slf4j.Slf4j;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 阻塞队列
 *
 * @author taoke
 * @date 2023/3/23
 */
@Slf4j
class BlockingQueue<T> {
    /**
     * 任务队列
     */
    private final Deque<T> queue = new ArrayDeque<>();
    /**
     * 锁
     */
    private final ReentrantLock lock = new ReentrantLock();
    /**
     * 队列满的waitSet
     */
    private final Condition fullWaitSet = lock.newCondition();
    /**
     * 队列为空的waitSet
     */
    private final Condition emptyWaitSet = lock.newCondition();
    /**
     * 队列容量
     */
    private final int capacity;

    public BlockingQueue(int capacity) {
        this.capacity = capacity;
    }

    /**
     * 带超时阻塞获取
     *
     * @param timeout 超时时间
     * @param unit    时间单位
     * @return 任务
     */
    public T poll(long timeout, TimeUnit unit) {
        lock.lock();
        try {
            // 将 timeout 统一转换为 纳秒
            long nanos = unit.toNanos(timeout);
            while (queue.isEmpty()) {
                try {
                    // 返回值是剩余时间
                    if (nanos <= 0) {
                        return null;
                    }
                    nanos = emptyWaitSet.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                }
            }
            T t = queue.removeFirst();
            fullWaitSet.signal();
            return t;
        } finally {
            lock.unlock();
        }
    }

    /**
     * 阻塞获取
     *
     * @return 任务
     */
    public T take() {
        lock.lock();
        try {
            while (queue.isEmpty()) {
                try {
                    emptyWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                }
            }
            T t = queue.removeFirst();
            fullWaitSet.signal();
            return t;
        } finally {
            lock.unlock();
        }
    }

    /**
     * 阻塞添加
     *
     * @param task 任务
     */
    public void put(T task) {
        lock.lock();
        try {
            while (queue.size() == capacity) {
                try {
                    log.debug("等待加入任务队列 {} ...", task);
                    fullWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                }
            }
            log.debug("加入任务队列 {}", task);
            queue.addLast(task);
            emptyWaitSet.signal();
        } finally {
            lock.unlock();
        }
    }

    /**
     * 带超时时间阻塞添加
     *
     * @param task     任务
     * @param timeout  超时时间
     * @param timeUnit 超时单位
     * @return 是否添加成功
     */
    public boolean offer(T task, long timeout, TimeUnit timeUnit) {
        lock.lock();
        try {
            long nanos = timeUnit.toNanos(timeout);
            while (queue.size() == capacity) {
                try {
                    if (nanos <= 0) {
                        return false;
                    }
                    log.debug("等待加入任务队列 {} ...", task);
                    nanos = fullWaitSet.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                }
            }
            log.debug("加入任务队列 {}", task);
            queue.addLast(task);
            emptyWaitSet.signal();
            return true;
        } finally {
            lock.unlock();
        }
    }

    /**
     * 获取队列大小
     *
     * @return 队列大小
     */
    public int size() {
        lock.lock();
        try {
            return queue.size();
        } finally {
            lock.unlock();
        }
    }

    /**
     * 尝试添加任务到队列
     *
     * @param rejectPolicy 拒绝策略
     * @param task         任务
     */
    public void tryPut(RejectPolicy<T> rejectPolicy, T task) {
        lock.lock();
        try {
            // 判断队列已满
            if (queue.size() == capacity) {
                rejectPolicy.reject(this, task);
            } else {
                //队列有空闲
                log.debug("加入任务队列 {}", task);
                queue.addLast(task);
                emptyWaitSet.signal();
            }
        } finally {
            lock.unlock();
        }
    }
}

3、自定义线程池

package com.tk.threadPool;

import lombok.extern.slf4j.Slf4j;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.TimeUnit;

/**
 * 自定义线程池
 *
 * @author taoke
 * @date 2023/3/23
 */
@Slf4j
class ThreadPool {
    /**
     * 任务队列
     */
    private final BlockingQueue<Runnable> taskQueue;
    /**
     * 工作线程集合
     */
    private final Set<Worker> workers = new HashSet<>();
    /**
     * 核心线程数
     */
    private final int coreSize;
    /**
     * 获取任务时的超时时间
     */
    private final long timeout;
    /**
     * 获取任务时的超时时间单位
     */
    private final TimeUnit timeUnit;
    /**
     * 拒绝策略
     */
    private final RejectPolicy<Runnable> rejectPolicy;

    public ThreadPool(int coreSize, int queueCapacity, long timeout, TimeUnit timeUnit, RejectPolicy<Runnable> rejectPolicy) {
        this.coreSize = coreSize;
        this.taskQueue = new BlockingQueue<>(queueCapacity);
        this.timeout = timeout;
        this.timeUnit = timeUnit;
        this.rejectPolicy = rejectPolicy;
    }

    /**
     * 执行任务
     * 工作线程已满可以尝试2种方式
     * 1) 死等 taskQueue.put(task);
     * 2) 带超时等待 taskQueue.tryPut(rejectPolicy, task);
     * 3) 让调用者放弃任务执行  log.debug("放弃{}", task);
     * 4) 让调用者抛出异常  throw new RuntimeException("任务执行失败 " + task);
     * 5) 让调用者自己执行任务  task.run();
     *
     * @param task 任务
     */
    public void execute(Runnable task) {
        // 当任务数没有超过 coreSize 时，直接交给 worker 对象执行
        // 如果任务数超过 coreSize 时，加入任务队列暂存
        synchronized (workers) {
            if (workers.size() < coreSize) {
                Worker worker = new Worker(task);
                log.debug("添加 worker{}, {}", worker, task);
                workers.add(worker);
                worker.start();
            } else {
                taskQueue.tryPut(rejectPolicy, task);
            }
        }
    }

    /**
     * 工作线程
     */
    class Worker extends Thread {
        private Runnable task;

        public Worker(Runnable task) {
            this.task = task;
        }

        /**
         * 执行任务
         * 1) 当 task 不为空，执行任务
         * 2) 当 task 执行完毕，再接着从任务队列获取任务并执行
         */
        @Override
        public void run() {
            while (task != null || (task = taskQueue.poll(timeout, timeUnit)) != null) {
                try {
                    log.debug("正在执行...{}", task);
                    task.run();
                } catch (Exception e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                } finally {
                    task = null;
                }
            }
            //任务执行完毕，移除当前线程
            synchronized (workers) {
                log.debug("worker 被移除{}", this);
                workers.remove(this);
            }
        }
    }
}

4、测试类

package com.tk.threadPool;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.TimeUnit;

/**
 * 测试类
 *
 * @author taoke
 * @date 2023/3/23
 */
@Slf4j
public class ThreadPoolTest {

    /**
     * 拒绝策略，队列中任务数量达到queueCapacity,任然有任务加入队列
     * 1. 死等
     * queue.put(task);
     * 2) 带超时等待
     * queue.offer(task, 2000, TimeUnit.MILLISECONDS);
     * 3) 让调用者放弃任务执行
     * log.debug("放弃{}", task);
     * 4) 让调用者抛出异常
     * throw new RuntimeException("任务执行失败 " + task);
     * 5) 让调用者自己执行任务
     * task.run();
     *
     * @param args 参数
     */
    public static void main(String[] args) {
        ThreadPool threadPool = new ThreadPool(2, 3, 1, TimeUnit.SECONDS, (queue, task) -> {
            boolean offer = queue.offer(task, 2000, TimeUnit.MILLISECONDS);
            log.debug("添加任务到队列是否成功:{}", offer);
        });
        for (int i = 0; i < 6; i++) {
            int j = i;
            threadPool.execute(() -> {
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                    log.debug(e.getMessage(), e);
                }
                log.debug("{}", j);
            });
        }
    }

}