Java 并发编程之自定义线程池

Java juc 大约 6753 字

代码

  • 核心线程
  • 阻塞队列
  • 拒绝策略
  • 未实现线程maxSize功能
public class CustomThreadPool {

    public static void main(String[] args) {
        ThreadPool threadPool = new ThreadPool(1, 1000, TimeUnit.MILLISECONDS, 1, (queue, task) -> {
            // 死等
//            queue.put(task);
            // 带超时时间
//            queue.offer(task, 1500, TimeUnit.MILLISECONDS);
            // 让调用者放弃任务执行
//            System.out.println("放弃任务"); // 什么都不用做,表示放弃
            // 让调用者抛出异常
//            throw new RuntimeException("任务执行失败#" + task); // 抛出异常后,之后的任务的都不执行了
            // 让调用者自己执行任务
            task.run();
        });
        for (int i = 0; i < 3; i++) {
            int finalI = i;
            threadPool.execute(() -> {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(finalI);
            });
        }
    }

}

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

class ThreadPool {
    // 任务队列
    private final BlockingQueue<Runnable> taskQueue;
    // 线程集合
    private final HashSet<Worker> workers = new HashSet<>();

    // 核心线程数
    private final int coreSize;

    // 获取任务的超时时间
    private final long timeout;

    private final TimeUnit timeUnit;

    private final RejectPolicy<Runnable> rejectPolicy;

    public void execute(Runnable task) {
        synchronized (workers) {
            // 当任务数没有超过 coreSize 交给 worker 执行
            // 如果任务数超过 coreSize 加入任务队列暂存
            if (workers.size() < coreSize) {
                Worker worker = new Worker(task);
                System.out.println("new worker#" + worker + ", task#" + task);
                workers.add(worker);
                worker.start();
            } else {
                taskQueue.tryPut(rejectPolicy, task);
            }
        }
    }

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

    class Worker extends Thread {

        private Runnable task;

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

        @Override
        public void run() {
            // 当任务不为空,执行任务
            // 当任务为空,从任务队列获取任务并执行
//            while (task != null || (task = taskQueue.take()) != null) {
            while (task != null || (task = taskQueue.poll(timeout, timeUnit)) != null) {
                try {
                    System.out.println(Thread.currentThread() + ", task executing#" + task);
                    task.run();
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    task = null;
                }
            }
            synchronized (workers) {
                System.out.println("remove worker#" + this);
                workers.remove(this);
            }
        }
    }
}

class BlockingQueue<T> {
    // 任务队列
    private final Deque<T> queue = new ArrayDeque<>();

    // 锁
    private final ReentrantLock lock = new ReentrantLock();

    // 生产者消费变量
    private final Condition fullWaitSet = lock.newCondition();

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

    // 容量
    private final int capacity;

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

    // 带超时的阻塞获取
    public T poll(long timeout, TimeUnit unit) {
        lock.lock();
        try {
            long nanos = unit.toNanos(timeout);
            while (queue.isEmpty()) {
                try {
                    if (nanos <= 0) {
                        return null;
                    }
                    nanos = emptyWaitSet.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            T t = queue.removeFirst();
            fullWaitSet.signal();
            return t;
        } finally {
            lock.unlock();
        }
    }

    // 阻塞添加
    public T take() {
        lock.lock();
        try {
            while (queue.isEmpty()) {
                try {
                    emptyWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            T t = queue.removeFirst();
            fullWaitSet.signal();
            return t;
        } finally {
            lock.unlock();
        }
    }

    // 阻塞放入
    public void put(T element) {
        lock.lock();
        try {
            while (size() == capacity) {
                try {
                    System.out.println("wait for adding task#" + element);
                    fullWaitSet.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("add task#" + element);
            queue.addLast(element);
            emptyWaitSet.signal();
        } finally {
            lock.unlock();
        }
    }

    public boolean offer(T task, long timeout, TimeUnit timeUnit) {
        lock.lock();
        try {
            long nanos = timeUnit.toNanos(timeout);
            while (size() == capacity) {
                try {
                    if (nanos <= 0) {
                        return false;
                    }
                    System.out.println("wait for adding task#" + task);
                    nanos = fullWaitSet.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("add task#" + 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 {
            // 队列满
            if (queue.size() == capacity) {
                rejectPolicy.reject(this, task);
            } else {// 有空闲
                System.out.println("add task#" + task);
                queue.addLast(task);
                emptyWaitSet.signal();
            }
        } finally {
            lock.unlock();
        }

    }
}
阅读 88 · 发布于 2021-11-09

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