线程池技术简单实现

如上一篇数据库链接池看到，由于没有使用线程池技术，需要频繁的创建和销毁线程，这无疑十分消耗和浪费系统的资源，正式基于这个，我们可以探索，摸索线程池的原理，自己建立个简单的demo来解惑。

线程池接口

package chapter04.connection_pool.thread_pool;/** * Created by tianjun on 2017/11/4. */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);    //渐少工作者线程    void removeWorker(int num);    //获得正在等待执行的任务数    int getJobSize();}

线程池实现

package chapter04.connection_pool.thread_pool;import java.util.*;import java.util.concurrent.atomic.AtomicLong;/** * Created by tianjun on 2017/11/4. */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;    // 线程池默认的数量    private static final int      DEFAULT_WORKER_NUMBERS = 5;    // 线程池最小的数量    private static final int      MIN_WORKER_NUMBERS     = 1;    // 这是一个工作列表，将会向里面插入工作    private final LinkedList<Job> jobs                   = new LinkedList<Job>();    // 工作者列表    private final List<Worker>    workers                = Collections.synchronizedList(new ArrayList<Worker>());    // 工作者线程的数量    private int                   workerNum              = DEFAULT_WORKER_NUMBERS;    // 线程编号生成    private AtomicLong            threadNum              = new AtomicLong();    public DefaultThreadPool() {        initializeWokers(DEFAULT_WORKER_NUMBERS);    }    public DefaultThreadPool(int num) {        workerNum = num > MAX_WORKER_NUMBERS ? MAX_WORKER_NUMBERS : num < MIN_WORKER_NUMBERS ? MIN_WORKER_NUMBERS : num;        initializeWokers(workerNum);    }    public void execute(Job job) {        if (job != null) {            // 添加一个工作，然后进行通知            synchronized (jobs) {                jobs.addLast(job);                jobs.notify();            }        }    }    public void shutdown() {        for (Worker worker : workers) {            worker.shutdown();        }    }    public void addWorkers(int num) {        synchronized (jobs) {            // 限制新增的Worker数量不能超过最大值            if (num + this.workerNum > MAX_WORKER_NUMBERS) {                num = MAX_WORKER_NUMBERS - this.workerNum;            }            initializeWokers(num);            this.workerNum += num;        }    }    public void removeWorker(int num) {        synchronized (jobs) {            if (num >= this.workerNum) {                throw new IllegalArgumentException("beyond workNum");            }            // 按照给定的数量停止Worker            int count = 0;            while (count < num) {                workers.get(count).shutdown();                count++;            }            this.workerNum -= count;        }    }    public int getJobSize() {        return jobs.size();    }    // 初始化线程工作者    private void initializeWokers(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();        }    }    // 工作者，负责消费任务    class Worker implements Runnable {        // 是否工作        private volatile boolean running = true;        public void run() {            while (running) {                Job job = null;                synchronized (jobs) {                    // 如果工作者列表是空的，那么就wait                    while (jobs.isEmpty()) {                        try {                            jobs.wait();                        } catch (InterruptedException ex) {                            // 感知到外部对WorkerThread的中断操作，返回                            Thread.currentThread().interrupt();                            return;                        }                    }                    // 取出一个Job                    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;        }    }}