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上节回顾

在上一节当中，已经实现了一个线程池，在本节当中，我们需要添加拒绝策略。这里使用到了策略模式的设计模式，因为拒绝策略是多种的，我们需要将这个权利下放给调用者（由调用者来指定我要采取哪种策略），而线程池只需要调用拒绝的接口即可。

步骤

（1）定义拒绝策略接口
（2）在线程池中加入拒绝策略参数
（3）自行调用测试

1.定义接口类

@FunctionalInterface
interface RejectPolicy<T>{//注意传递参数void reject(BlockQueue<T> queue,Runnable task);
}

2.线程池中添加接口以及调用方法

@Slf4j
class ThreadPool {//任务队列private BlockQueue<Runnable> taskQueue;//线程集合 我们需要对线程做一个包装private HashSet<Worker> workers = new HashSet<>();//核心线程数量private long coreSize;//超时时间private long timeout;//时间单位private TimeUnit timeUnit;//自定义拒绝策略private RejectPolicy<Runnable> rejectPolicy;public ThreadPool(int queueCapacity,long coreSize,long timeout,TimeUnit timeUnit){this.taskQueue = new BlockQueue<>(queueCapacity);this.coreSize = coreSize;this.timeout = timeout;this.timeUnit = timeUnit;this.rejectPolicy = (queue, task) -> {throw new RuntimeException();};}public ThreadPool(int queueCapacity,long coreSize,long timeout,TimeUnit timeUnit,RejectPolicy<Runnable> rejectPolicy){taskQueue = new BlockQueue<>(queueCapacity);this.coreSize = coreSize;this.timeout = timeout;this.timeUnit = timeUnit;this.rejectPolicy = rejectPolicy;}//执行任务public void execute(Runnable task){//当任务数量尚未超过coreSizesynchronized (workers){if (workers.size() < coreSize){log.info("创建工作线程{}",task);Worker worker = new Worker(task);workers.add(worker);worker.start();}else{log.info("加入到任务队列{}",task);//有可能会阻塞在这里 进而将主线程阻塞掉//taskQueue.put(task);//这里会有很多种策略自定义策略//策略模式：操作抽象成接口实现代码是传过来不会写死taskQueue.tryPut(rejectPolicy,task);//rejectPolicy.reject(taskQueue,task);}}}class Worker extends Thread{private Runnable task;public Worker(Runnable task){this.task = task;}@Overridepublic void run() {while (task != null || (task = taskQueue.poll(timeout,timeUnit)) != null){try {log.info("正在执行...{}",task);//执行任务task.run();}catch (Exception e){System.out.println(e.getMessage());}finally {//不要忘记这一步task = null;}}synchronized (workers){log.info("worker被移除{}",this);workers.remove(this);}}}
}

3.main测试

@Slf4j
public class TestPool {//阻塞队列是平衡生产者和消费者之间的中介//任务数量超过任务队列的情况public static void main(String[] args) {ThreadPool threadPool = new ThreadPool(10, 2, 1000, TimeUnit.MICROSECONDS, (queue, task) -> {//1.死等queue.put(task);//2.超时等待queue.offer(task, 1500, TimeUnit.MICROSECONDS);//3.调用者自己放弃// log.debug("放弃{}",task);//4.调用者抛异常//throw new RuntimeException("task执行失败" + task);//5.调用者自己执行task.run();});for (int i = 0; i < 20; i++) {int j = i;//主线程可能会在这里阻塞threadPool.execute(() -> {try {Thread.sleep(30000);} catch (InterruptedException e) {throw new RuntimeException(e);}TestPool.log.debug("{}", j);});}}
}