自定义线程池

// 拒绝策略
@FunctionalInterface
interface RejectPolicy<T> {
    void reject(BlockingQueue<T> queue, T task);
}

@Slf4j
public class TestPoll {
    public static void main(String[] args) {
        CustomThreadPool customThreadPool = new CustomThreadPool(1, 1000, TimeUnit.MILLISECONDS, 1, ((queue, task) -> {
            // 死等  queue.put(task);
            // 带超时等待 queue.offer(task, 1500, TimeUnit.MILLISECONDS);
            // 让调用者放弃任务执行  log.debug("{}", task);
            // 让调用者抛出异常 throw new RuntimeException("任务执行失败！" + task);
            // 让调用者自己执行任务 task.run();
        }));

        for (int i = 0; i < 3; i++) {
            int j = i;
            customThreadPool.execute(() -> {
                try {
                    Thread.sleep(1000L);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
                log.debug("{}", j);
            });
        }
    }
}

/**
 * 自定义线程池
 */
@Slf4j
@NoArgsConstructor
@AllArgsConstructor
class CustomThreadPool {

    // 任务队列
    private BlockingQueue<Runnable> taskQueue;

    // 线程集合
    private HashSet<Worker> workers = new HashSet<>();

    // 核心线程数
    private int coreSize;

    // 获取任务时的超时时间
    private long timeout;

    //超时单位时间
    private TimeUnit timeUnit;

    //拒绝策略
    private RejectPolicy<Runnable> rejectPolicy;

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

    // 执行任务
    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("新增 worker{}, {}", worker, task);
                workers.add(worker);
                worker.start();
            } else {
                taskQueue.tryPut(rejectPolicy, task);
            }
        }
    }

    class Worker extends Thread {

        //任务对象
        private Runnable task;

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

        // 执行任务
        @Override
        public void run() {

            // 当任务对象不为空 || 任务队列中不为空
            while (task != null || (task = taskQueue.poll(timeout, timeUnit)) != null) {
                try {
                    log.debug("正在执行...{}", task);
                    task.run();
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    task = null;
                }
            }
            synchronized (workers) {
                log.debug("worker 被移除{}", this);
                workers.remove(this);
            }
        }
    }
}

/**
 * 阻塞队列
 */
@Slf4j
class BlockingQueue<T> {

    // 1. 任务队列
    private Deque<T> queue = new ArrayDeque<>();

    // 2. 可重入锁
    private ReentrantLock lock = new ReentrantLock();

    // 3. 生产者条件变量
    private Condition fullWaitSet = lock.newCondition();

    // 4. 消费者条件变量
    private Condition emptyWaitSet = lock.newCondition();

    // 5. 容量
    private int capcity;

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

    // 带超时阻塞获取
    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 {
                    if (nanos <= 0) {
                        return null;
                    }
                    // 返回值是剩余时间
                    nanos = emptyWaitSet.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            T t = queue.removeFirst();
            fullWaitSet.signal();
            return t;
        } finally {
            lock.unlock();
        }
    }

    // 阻塞获取
    public T take() {
        //添加锁
        lock.lock();
        try {
            while (queue.isEmpty()) {
                try {
                    //使调用该方法的线程等待，直到有其它线程调用了该条件对象的signal方法或者线程被中断了。
                    emptyWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //返回队列第一个元素并删除
            T t = queue.removeFirst();
            //signal方法调用后，会唤醒该Condition对象上的一个等待线程。如果有任何线程在此条件下等待，则选择其中一个线程唤醒。
            fullWaitSet.signal();
            return t;
        } finally {
            //释放锁
            lock.unlock();
        }
    }

    // 阻塞添加
    public void put(T task) {
        lock.lock();
        try {
            while (queue.size() == capcity) {
                try {
                    log.debug("等待加入任务队列 {} ...", task);
                    fullWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            log.debug("加入任务队列 {}", task);
            //添加到最后一个
            queue.addLast(task);
            emptyWaitSet.signal();
        } finally {
            lock.unlock();
        }
    }

    // 带超时时间阻塞添加
    public boolean offer(T task, long timeout, TimeUnit timeUnit) {
        lock.lock();
        try {
            long nanos = timeUnit.toNanos(timeout);
            while (queue.size() == capcity) {
                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("加入任务队列 {}", task);
            queue.addLast(task);
            emptyWaitSet.signal();
            return true;
        } finally {
            lock.unlock();
        }
    }

    public int size() {
        lock.lock();
        try {
            return queue.size();
        } finally {
            lock.unlock();
        }
    }

    public void tryPut(RejectPolicy<T> rejectPolicy, T task) {
        lock.lock();
        try {
            // 判断队列是否满
            if (queue.size() == capcity) {
                rejectPolicy.reject(this, task);
            } else {
                // 有空闲
                log.debug("加入任务队列 {}", task);
                queue.addLast(task);
                emptyWaitSet.signal();
            }
        } finally {
            lock.unlock();
        }
    }
}