Java 实现线程池

ThreadPool 接口

ThreadPool.java

package ThreadPool;

public interface ThreadPool<Job extends Runnable> {
    //执行一个Job,这个Job需要实现Runnable
    void execute(Job job);
    //关闭线程池
    void shutdown();
    //增加工作者线程
    void addWorkers(int num);
    //减少工作者线程
    void removeWorkers(int num);
    //得到正在等待执行的任务数
    int getJobSize();
}

线程池的默认实现

DefaultThreadPool.java

package ThreadPool;

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

public class DefaultThreadPool<Job extends Runnable> implements ThreadPool<Job> {
    //线程池最大限制数
    private static final int MAX_WORKER_NUMBERS = 10;
    //线程池默认线程数量
    private static final int DEFAULT_WORKER_NUMBERS = 5;
    //线程池最小线程数量
    private static final int MIX_WORKER_NUMBERS = 1;
    //任务队列
    private final LinkedList<Job> jobs = new LinkedList<Job>();
    //工作者/线程（执行任务）队列
    private final List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());
    //工作者/线程数
    private int workNum = DEFAULT_WORKER_NUMBERS;
    //线程编号生成
    private AtomicLong threadNum = new AtomicLong();

    public DefaultThreadPool(){
        initializeWorkers(DEFAULT_WORKER_NUMBERS);
    }
    public DefaultThreadPool(int num){
        workNum = num > MAX_WORKER_NUMBERS ? MAX_WORKER_NUMBERS : num < MIX_WORKER_NUMBERS ? MIX_WORKER_NUMBERS : num;
        initializeWorkers(workNum);
    }
    //初始化即添加工作线程
    private void initializeWorkers(int num){
        for (int i = 0; i < num; i++){
            Worker worker = new Worker();
            workers.add(worker);
            Thread thread = new Thread(worker, "ThreadPool-Worker-" + threadNum.incrementAndGet());
            thread.start();
        }
    }
    //执行任务
    @Override
    public void execute(Job job) {
        if (job != null){
            synchronized (jobs){
                //在任务队列添加一个任务，然后通知
                jobs.addLast(job);
                jobs.notify();
            }
        }
    }

    @Override
    public void shutdown() {
        for (Worker worker : workers){
            worker.shutdown();
        }
    }

    @Override
    public void addWorkers(int num) {
        synchronized (jobs){
            if (num + this.workNum > MAX_WORKER_NUMBERS){
                num = MAX_WORKER_NUMBERS - this.workNum;
            }
            initializeWorkers(num);
            this.workNum += num;
        }
    }

    @Override
    public void removeWorkers(int num) {
        synchronized (jobs){
            if (num > this.workNum){
                throw new IllegalArgumentException("beyond workNum");
            }
            int count = 0;
            while (count < num){
                Worker worker = workers.get(count);
                if (workers.remove(worker)){
                    worker.shutdown();
                    count++;
                }
            }
            this.workNum -= count;
        }
    }

    @Override
    public int getJobSize() {
        return jobs.size();
    }
    class Worker implements Runnable{
        private volatile boolean running = true;

        /**
         * When an object implementing interface <code>Runnable</code> is used
         * to create a thread, starting the thread causes the object's
         * <code>run</code> method to be called in that separately executing
         * thread.
         * <p>
         * The general contract of the method <code>run</code> is that it may
         * take any action whatsoever.
         *
         * @see Thread#run()
         */
        @Override
        public void run() {
            while (running){
                Job job = null;
                synchronized (jobs){
                    while (jobs.isEmpty()){
                        try{
                            jobs.wait();
                        }catch (InterruptedException ex){
                            Thread.currentThread().interrupt();
                            return;
                        }
                    }
                    job = jobs.removeFirst();
                }
                if (job != null){
                    try {
                        job.run();
                    }catch (Exception ex){
                        //忽略 Job 执行中的Exception
                    }
                }
            }
        }

        public void shutdown(){
            running = false;
        }
    }
}