# 给线程池增加自动扩充,闲时自动回收线程的功能 首先我们给SimpleThreadPool定义三个成员属性：最小线程数量，活跃线程数量，最大线程数量。   同样构造方法修改一下：  我们程序默认开启最小线程数量，当他不够用的时候我们扩充到活跃线程数量，当活跃线程数量不够的时候我们扩充到最大线程数量。 那么应该在什么位置控制THREAD_QUEUE呢？当然是由SimpleThreadPool控制了，所以我们用SimpleThreadPool继承Thread来实现他的run方法：  运行效果如下：  全部代码如下： ```java package com.thread.thread22; import java.util.ArrayList; import java.util.Iterator; import java.util.LinkedList; import java.util.List; import java.util.concurrent.atomic.AtomicInteger; import java.util.stream.IntStream; /** * 自定义简单线程池 * 任务队列、拒绝策略 */ public class SimpleThreadPool extends Thread { /** * 最小线程数量 */ private int min; /** * 活跃线程数量 */ private int active; /** * 最大线程数量 */ private int max; /** * 传参线程池大小(当前线程池中线程的数量) */ private int size; /** * 线程队列的大小 */ private final int queueSize; /** * 拒绝策略 */ private final DiscardPolicy discardPolicy; /** * 线程池是否被销毁 */ private volatile boolean destroy = false; /** * 默认最小线程数量 */ private static final int DEFAULT_MIN_SIZE = 4; /** * 默认活跃线程数量 */ private static final int DEFAULT_ACTIVE_SIZE = 8; /** * 默认最大线程数量 */ private static final int DEFAULT_MAX_SIZE = 12; /** * 默认线程队列的大小 */ private static final int DEFAULT_TASK_QUEUE_SIZE = 2000; /** * 默认拒绝策略-抛出异常 */ public static final DiscardPolicy DEFAULT_DISCARD_POLICY = () -> { throw new DiscardException("Discard This Task."); }; /** * 线程名自增序号 */ private static AtomicInteger sequence = new AtomicInteger(); /** * 线程名前缀 */ private static final String THREAD_PREFIX = "SIMPLE_THREAD_POOL-"; /** * 线程组 */ private static final ThreadGroup GROUP = new ThreadGroup("Pool_Group"); /** * 任务队列 */ private static final LinkedList<Runnable> TASK_QUEUE = new LinkedList<>(); /** * 线程队列 */ private static final List<WorkerTask> THREAD_QUEUE = new ArrayList<>(); public SimpleThreadPool() { this(DEFAULT_MIN_SIZE, DEFAULT_ACTIVE_SIZE, DEFAULT_MAX_SIZE, DEFAULT_TASK_QUEUE_SIZE, DEFAULT_DISCARD_POLICY); } /** * 构造方法 * * @param min 最小线程数量 * @param active 活跃线程数量 * @param max 最大线程数量 * @param queueSize 线程队列的大小 * @param discardPolicy 拒绝策略 */ public SimpleThreadPool(int min, int active, int max, int queueSize, DiscardPolicy discardPolicy) { this.min = min; this.active = active; this.max = max; this.queueSize = queueSize; this.discardPolicy = discardPolicy; init(); } @Override public void run() { while (!destroy) { System.out.printf("Pool#Min:%d,Active:%d,Max:%d,Current:%d,QueueSize:%d\n", this.min, this.active, this.max, this.size, TASK_QUEUE.size()); try { Thread.sleep(5_000L); // 任务队列数量过大，线程队列的数量扩充到active if (size < active && active < TASK_QUEUE.size()) { IntStream.range(size, active).forEach(i -> createWorkTask()); size = active; System.out.println("The Pool incremented to active."); } // 任务队列数量过大，线程队列的数量扩充到max else if (size < max && max < TASK_QUEUE.size()) { IntStream.range(active, max).forEach(i -> createWorkTask()); size = max; System.out.println("The Pool incremented to max."); } // 防止新插入任务队列的任务使用线程队列中的线程执行任务。 synchronized (THREAD_QUEUE) { // 任务队列数量为空，线程队列的数量减少到active if (size > active && TASK_QUEUE.isEmpty()) { System.out.println("=========Reduce========="); int releaseSize = size - active; for (Iterator<WorkerTask> it = THREAD_QUEUE.iterator(); it.hasNext(); ) { if (releaseSize <= 0) { break; } WorkerTask task = it.next(); task.interrupt(); task.close(); it.remove(); releaseSize--; } size = active; } } } catch (InterruptedException e) { e.printStackTrace(); } } } private void init() { IntStream.range(0, this.min).forEach(i -> createWorkTask()); this.size = this.min; this.start(); } private void createWorkTask() { WorkerTask task = new WorkerTask(GROUP, THREAD_PREFIX + (sequence.getAndIncrement())); task.start(); THREAD_QUEUE.add(task); } /** * 提交任务 * * @param runnable 任务 */ public void submit(Runnable runnable) { // 如果线程池被销毁，不能添加任务到任务队列 if (destroy) { throw new IllegalThreadStateException("The thread pool already destroy and not allow submit task."); } synchronized (TASK_QUEUE) { // 任务队列数量超过阈值，则执行拒绝策略 if (TASK_QUEUE.size() > queueSize) { discardPolicy.discard(); } TASK_QUEUE.addLast(runnable); TASK_QUEUE.notifyAll(); } } /** * 关闭线程池中的线程 * * @throws InterruptedException */ public void shutdown() throws InterruptedException { // 当任务队列还有任务，则稍微等待。 while (!TASK_QUEUE.isEmpty()) { Thread.sleep(50); } // 判断线程中有没有正在运行的任务 synchronized (THREAD_QUEUE) { int initVal = THREAD_QUEUE.size(); while (initVal > 0) { for (WorkerTask task : THREAD_QUEUE) { if (task.getTaskState() == TaskState.BLOCKED) { task.interrupt(); task.close(); initVal--; } else { Thread.sleep(10); } } } } System.out.println("Group active count is " + GROUP.activeCount()); this.destroy = true; System.out.println("The thread pool disposed."); } public boolean isDestroy() { return destroy; } public int getMin() { return min; } public int getMax() { return max; } public int getActive() { return active; } public int getSize() { return size; } public int getQueueSize() { return queueSize; } /** * 封装任务类 */ private static class WorkerTask extends Thread { private volatile TaskState taskState = TaskState.FREE; public TaskState getTaskState() { return this.taskState; } public WorkerTask(ThreadGroup group, String name) { super(group, name); } @Override public void run() { OUTER: while (this.taskState != TaskState.DEAD) { Runnable runnable; synchronized (TASK_QUEUE) { // 任务队列为空，则进入阻塞状态 while (TASK_QUEUE.isEmpty()) { try { this.taskState = TaskState.BLOCKED; TASK_QUEUE.wait(); } catch (InterruptedException e) { System.out.println("Closed."); break OUTER; } } // 任务队列不为空，取出任务 runnable = TASK_QUEUE.removeFirst(); } // 任务不为空，则执行任务 if (runnable != null) { this.taskState = TaskState.RUNNING; runnable.run(); this.taskState = TaskState.FREE; } } } public void close() { this.taskState = TaskState.DEAD; } } /** * 线程状态 */ private enum TaskState { FREE, RUNNING, BLOCKED, DEAD } /** * 拒绝策略 */ public interface DiscardPolicy { void discard() throws DiscardException; } /** * 拒绝策略异常 */ public static class DiscardException extends RuntimeException { public DiscardException(String message) { super(message); } } public static void main(String[] args) throws InterruptedException { SimpleThreadPool threadPool = new SimpleThreadPool(); /*SimpleThreadPool threadPool = new SimpleThreadPool(6, 10, SimpleThreadPool.DEFAULT_DISCARD_POLICY);*/ IntStream.rangeClosed(1, 40).forEach(i -> { threadPool.submit(() -> { System.out.printf("The runnable %d be serviced by %s start.\n", i, Thread.currentThread().getName()); try { Thread.sleep(3_000L); } catch (InterruptedException e) { e.printStackTrace(); } System.out.printf("The runnable %d be serviced by %s finished.\n", i, Thread.currentThread().getName()); }); }); Thread.sleep(30_000L); threadPool.shutdown();// 关闭线程池中的线程 /*threadPool.submit(() -> System.out.println("线程池被销毁，不能添加任务到任务队列"));*/ } } ``` java的多线程基础就暂时学完了，后面还要继续学习多线程的设计模式以及jdk并发包的知识。