JUC学习-线程池部分

标签：JUC task System 学习线程 println pool out

自定义线程池

package com.appletree24;  
  
import java.util.ArrayDeque;  
import java.util.Deque;  
import java.util.HashSet;  
import java.util.concurrent.ExecutionException;  
import java.util.concurrent.TimeUnit;  
import java.util.concurrent.locks.Condition;  
import java.util.concurrent.locks.ReentrantLock;  
  
class Main {  
    public static void main(String[] args) throws ExecutionException, InterruptedException {  
        ThreadPool threadPool = new ThreadPool(2, 1000, TimeUnit.MICROSECONDS, 5, (queue, task) -> {  
            //带超时等待  
//            queue.offer(task,500,TimeUnit.MILLISECONDS);  
        });  
        for (int i = 0; i < 10; i++) {  
            int j = i;  
            threadPool.execute(() -> {  
                try {  
                    Thread.sleep(1000L);  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
                System.out.println(j);  
            });  
        }  
    }  
}  
  
//策略模式接口 此处使用策略模式是因为在实现拒绝策略时，有许多种拒绝的方式，这些方式如果不使用恰当的模式，就需要大量的if..else来编写  
//且方式数量大于4个，会造成类膨胀的问题，推荐使用混合模式  
//https://www.runoob.com/design-pattern/strategy-pattern.html  
@FunctionalInterface  
interface RejectPolicy<T> {  
    void reject(BlockingQueue<T> queue, T task);  
}  
  
class ThreadPool {  
    //任务队列  
    private BlockingQueue<Runnable> taskQueue;  
    //线程集合  
    private HashSet<Worker> workers = new HashSet<>();  
  
    //线程数  
    private int coreSize;  
  
    //超时时间  
    private long timeout;  
  
    private TimeUnit timeUnit;  
    private RejectPolicy<Runnable> rejectPolicy;  
  
    //执行任务  
    public void execute(Runnable task) {  
        //当任务数未超过核心线程数时，直接交给Worker对象执行  
        //如果超过，则加入阻塞任务队列，暂存起来  
        synchronized (workers) {  
            if (workers.size() < coreSize) {  
                Worker worker = new Worker(task);  
                workers.add(worker);  
                worker.start();  
            } else {  
                //第一种选择死等  
//                taskQueue.put(task);  
                //第二种为超时等待  
                //第三种为消费者放弃任务执行  
                //第四种为主线程抛出异常  
                //第五种让调用者自行执行任务  
                taskQueue.tryPut(rejectPolicy, task);  
            }  
        }  
    }  
  
    public ThreadPool(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;  
    }  
  
    class Worker extends Thread {  
        private Runnable task;  
  
        public Worker(Runnable task) {  
            this.task = task;  
        }  
  
        @Override  
        public void run() {  
            //执行任务  
            //1.当传递过来的task不为空，执行任务  
            //2.当task执行完毕，再接着取下一个任务并执行  
            while (task != null || (task = taskQueue.poll(1000, TimeUnit.MILLISECONDS)) != null) {  
                try {  
                    task.run();  
                } catch (Exception e) {  
                    e.printStackTrace();  
                } finally {  
                    task = null;  
                }  
            }  
            synchronized (workers) {  
                workers.remove(this);  
            }  
        }  
    }  
}  
  
class BlockingQueue<T> {  
    //1. 任务队列  
    private final Deque<T> queue = new ArrayDeque<>();  
  
    //2. 锁  
    private final ReentrantLock lock = new ReentrantLock();  
  
    //3. 生产者条件变量  
    private final Condition fullWaitSet = lock.newCondition();  
  
    //4. 消费者条件变量  
    private final Condition emptyWaitSet = lock.newCondition();  
  
    //5. 容量上限  
    private int capcity;  
  
    public BlockingQueue(int capcity) {  
        this.capcity = capcity;  
    }  
  
    //带超时的等待获取  
    public T poll(long timeout, TimeUnit unit) {  
        lock.lock();  
        long nanos = unit.toNanos(timeout);  
        try {  
            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();  
        }  
    }  
  
    //消费者拿取任务的方法  
    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();  
        }  
    }  
  
    //阻塞添加  
    public void put(T task) {  
        lock.lock();  
        try {  
            while (queue.size() == capcity) {  
                try {  
                    fullWaitSet.await();  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
            queue.offerLast(task);  
            //添加完后唤醒消费者等待  
            emptyWaitSet.signal();  
        } finally {  
            lock.unlock();  
        }  
    }  
  
    //带超时时间的阻塞添加  
    public boolean offer(T task, long timeout, TimeUnit unit) {  
        lock.lock();  
        try {  
            long nanos = unit.toNanos(timeout);  
            while (queue.size() == capcity) {  
                try {  
                    if (nanos <= 0) return false;  
                    nanos = fullWaitSet.awaitNanos(nanos);  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
            queue.offerLast(task);  
            //添加完后唤醒消费者等待  
            emptyWaitSet.signal();  
            return true;  
        } finally {  
            lock.unlock();  
        }  
    }  
  
  
    //获取当前阻塞队列大小  
    public int size() {  
        lock.lock();  
        try {  
            return queue.size();  
        } finally {  
            lock.unlock();  
        }  
    }  
  
    public void tryPut(RejectPolicy<T> rejectPolicy, T task) {  
        lock.lock();  
        try {  
            //判断队列是否已满  
            if (queue.size() == capcity) {  
                rejectPolicy.reject(this, task);  
            } else {  
                queue.addLast(task);  
                emptyWaitSet.signal();  
            }  
        } finally {  
            lock.unlock();  
        }  
    }  
}

上述的自定义线程池虽然能够执行完毕主线程给予的任务，但任务全部执行结束后，开辟的线程池内核心线程仍然在运行，并没有结束，这是因为目前线程池中的take方法仍然为不会有超时等待的take方法，造成了死等，需要为其加入超时停止的功能。也就是替代take()的poll()

JDK自带线程池

介绍

ThreadPoolExecutor使用int的高三位表示线程池状态，低29位表示线程数量

在ThreadPoolExecutor中，同样也存在拒绝策略。其图结构如下：

其中接口就对应着在自定义线程池中实现的策略模式接口，下面的四个实现类就对应着四种不同的拒绝方式：

利用工具类创建固定大小线程池

利用工具类创建带缓冲的线程池

从源码可以看出，带缓冲的线程池中缓冲队列的使用的是一个名为SynchronousQueue的队列，这个队列的特点如下：队列不具有容量，当没有线程来取时，是无法对其内部放入数据的，例如队列内部已有一个数字1，但此时没有线程取走，则线此队列目前并不能继续存入数据，直到1被取走

利用工具类创建单线程线程池

从源码可以看出，单线程线程池中核心线程数与最大线程数相等，即不存在应急线程。只能解决一个任务
那么这个线程池和我自己创建一个线程的线程池有什么区别呢？区别如下：

ThreadPoolExecutor-submit method

public static void main(String[] args) throws ExecutionException, InterruptedException {  
    ExecutorService pool = Executors.newFixedThreadPool(2);  
    Future<String> result = pool.submit(() -> {  
        System.out.println("running");  
        Thread.sleep(1000);  
        return "ok";  
    });  
    System.out.println(result.get());  
}

submit方法可以传入Runnable和Callable类型的参数，并且将线程内部所执行任务的结果返回，用Future包装

ThreadPoolExecutor-invokeAll

public static void main(String[] args) throws ExecutionException, InterruptedException {  
    ExecutorService pool = Executors.newFixedThreadPool(2);  
    List<Future<String>> results = pool.invokeAll(Arrays.asList(() -> {  
                System.out.println("begin");  
                Thread.sleep(1000);  
                return "1";  
            },  
            () -> {  
                System.out.println("begin");  
                Thread.sleep(500);  
                return "2";  
            }));  
    results.forEach(f -> {  
        try {  
            System.out.printf(f.get());  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        } catch (ExecutionException e) {  
            e.printStackTrace();  
        }  
    });  
}

invokeAll方法可以传入任务的集合，同样的任务的返回值也会以列表形式返回

ThreadPoolExecutor-invokeAny

public static void main(String[] args) throws ExecutionException, InterruptedException {  
    ExecutorService pool = Executors.newFixedThreadPool(2);  
    String result = pool.invokeAny(Arrays.asList(() -> {  
                System.out.println("begin");  
                Thread.sleep(1000);  
                return "1";  
            },  
            () -> {  
                System.out.println("begin");  
                Thread.sleep(500);  
                return "2";  
            }));  
    pool.awaitTermination(1000, TimeUnit.MILLISECONDS);  
    System.out.println(result);  
}

invokeAny方法同样可以传入任务的集合，只不过最后返回的结果并不是任务的结果集合，而是最早完成的那个任务的结果。

ThreadPoolExecutor-shutdown

public static void main(String[] args) throws ExecutionException, InterruptedException {  
    ExecutorService pool = Executors.newFixedThreadPool(2);  
    List<Future<String>> results = pool.invokeAll(Arrays.asList(() -> {  
                System.out.println("begin");  
                Thread.sleep(1000);  
                return "1";  
            },  
            () -> {  
                System.out.println("begin");  
                Thread.sleep(500);  
                return "2";  
            }));  
    pool.shutdown();  
    results.forEach(f -> {  
        try {  
            System.out.println(f.get());  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        } catch (ExecutionException e) {  
            e.printStackTrace();  
        }  
    });  
}

shutdown方法会将线程池的状态变为SHUTDOWN

不会接受新任务
但已提交的任务会执行完
此方法不会阻塞调用线程的执行

ThreadPoolExecutor-shutdownNow

public static void main(String[] args) throws ExecutionException, InterruptedException {  
    ExecutorService pool = Executors.newFixedThreadPool(2);  
    List<Future<String>> results = pool.invokeAll(Arrays.asList(() -> {  
                System.out.println("begin");  
                Thread.sleep(1000);  
                return "1";  
            },  
            () -> {  
                System.out.println("begin");  
                Thread.sleep(500);  
                return "2";  
            }));  
    List<Runnable> runnables = pool.shutdownNow();  
    results.forEach(f -> {  
        try {  
            System.out.println(f.get());  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        } catch (ExecutionException e) {  
            e.printStackTrace();  
        }  
    });  
}

shutdownNow方法会将线程池状态变为STOP

不会接受新任务
会将队列中现有的任务返回
并且用interrupt方法中断正在执行的任务

标签：JUC,task,System,学习,线程,println,pool,out
From： https://www.cnblogs.com/appletree24/p/17142610.html