线程池

为什么要建立线程池？

 

在多线程项目中，如果建立的线程过多，反而可能导致运行速度大大减慢，这是由于线程建立所花费的时间和资源都比较多。
所以我们在多线程中必须很好地来管理线程， 在很好利用多线程能“同步工作”的好处之外，更有效地提高程序运行速度。

 

线程池是什么？

 

线程池是指具有固定数量的线程组成的一种组件。这些线程用来循环执行多个应用逻辑。

 

怎么建立线程池？

 

线程池主要包括4个部分，它们是：
1. 线程管理
 

主要是用来建立，启动，销毁工作线程和把工作任务加入工作线程。

 

2. 工作线程
 

它是真正的线程类，运行工作任务。

 

3. 工作队列
 

它是用来封装线程的容器。

4. 工作任务
 

它是实现应用逻辑的具体类。

 

流程图：

 

 线程管理类：

<SPAN style="COLOR: #3366ff">import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * ThreadPoolManager.java
 *
 */

/**
 * the thread pool manager, is responsible for starting and stopping the work thread.
 *
 * @author  gray
 * @version 1.0
 */
public class ThreadPoolManager {

    private static final int DEFAULT_POOL_SIZE = 4;
    private List<WorkThread> threadPool;
    private Queue<Task> taskQueue;
    private int poolSize;

    public ThreadPoolManager() {
        this(DEFAULT_POOL_SIZE);
    }

    public ThreadPoolManager(int poolSize) {
        if(poolSize <= 0) {
            this.poolSize = DEFAULT_POOL_SIZE;
        }else {
            this.poolSize = poolSize;
        }
        threadPool = new ArrayList<WorkThread>(this.poolSize);
        taskQueue = new ConcurrentLinkedQueue<Task>();
        startup();
    }

    public void startup() {
        System.out.println("start work thread...");
        synchronized(taskQueue) {
            for(int i = 0; i < this.poolSize; i++) {
                WorkThread workThread = new WorkThread(taskQueue);
                threadPool.add(workThread);
                workThread.start();
            }
        }
    }

    public void shutdown() {
        System.out.println("shutdown work thread...");
        synchronized(taskQueue) {
            for(int i = 0; i < this.poolSize; i++) {
                threadPool.get(i).shutdown();
            }

            System.out.println("done...");
        }
    }

    public void addTask(Task task) {
        synchronized(taskQueue) {
            taskQueue.add(task);
            taskQueue.notify();
        }
    }
}</SPAN>

import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * ThreadPoolManager.java
 *
 */

/**
 * the thread pool manager, is responsible for starting and stopping the work thread.
 * 
 * @author  gray
 * @version 1.0
 */
public class ThreadPoolManager {

	private static final int DEFAULT_POOL_SIZE = 4;
	private List<WorkThread> threadPool;
	private Queue<Task> taskQueue;
	private int poolSize;
	
	public ThreadPoolManager() {
		this(DEFAULT_POOL_SIZE);
	}
	
	public ThreadPoolManager(int poolSize) {
		if(poolSize <= 0) {
			this.poolSize = DEFAULT_POOL_SIZE;
		}else {
			this.poolSize = poolSize;
		}
		threadPool = new ArrayList<WorkThread>(this.poolSize);
		taskQueue = new ConcurrentLinkedQueue<Task>();
		startup();
	}
	
	public void startup() {
		System.out.println("start work thread...");
		synchronized(taskQueue) {
			for(int i = 0; i < this.poolSize; i++) {
				WorkThread workThread = new WorkThread(taskQueue);
				threadPool.add(workThread);
				workThread.start();
			}
		}
	}
	
	public void shutdown() {
		System.out.println("shutdown work thread...");
		synchronized(taskQueue) {
			for(int i = 0; i < this.poolSize; i++) {
				threadPool.get(i).shutdown();
			}			
			
			System.out.println("done...");
		}
	}
	
	public void addTask(Task task) {
		synchronized(taskQueue) {
			taskQueue.add(task);
			taskQueue.notify();
		}
	}
}

 

工作线程类：

<SPAN style="COLOR: #3366ff">import java.util.Queue;

/**
 * WorkThread.java
 *
 */

/**
 * the work thread used pull the task of task queue, and execute it.
 *
 * @author  gray
 * @version 1.0
 */
public class WorkThread extends Thread {

    private boolean shutdown = false;
    private Queue<Task> queue;

    public WorkThread(Queue<Task> queue) {
        this.queue = queue;
    }

    public void run() {
        while(!shutdown) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e1) {
                e1.printStackTrace();
            }
            System.out.println(Thread.currentThread() + " is running...");
            synchronized(queue) {
                if(!queue.isEmpty()) {
                    Task task = queue.poll();
                    task.execute();
                }else {
                    try {
                        queue.wait(1000);
                        System.out.println(Thread.currentThread() + " wait...");
                    }catch(InterruptedException e) {

                    }
                }
            }
        }
    }

    public void shutdown() {
        shutdown = true;
    }
}</SPAN>

import java.util.Queue;

/**
 * WorkThread.java
 *
 */

/**
 * the work thread used pull the task of task queue, and execute it.
 * 
 * @author  gray
 * @version 1.0
 */
public class WorkThread extends Thread {

	private boolean shutdown = false;
	private Queue<Task> queue;
	
	public WorkThread(Queue<Task> queue) {
		this.queue = queue;
	}
	
	public void run() {
		while(!shutdown) {
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e1) {
				e1.printStackTrace();
			}
			System.out.println(Thread.currentThread() + " is running...");
			synchronized(queue) {
				if(!queue.isEmpty()) {
					Task task = queue.poll();
					task.execute();
				}else {
					try {
						queue.wait(1000);
						System.out.println(Thread.currentThread() + " wait...");
					}catch(InterruptedException e) {
						
					}
				}
			}
		}
	}
	
	public void shutdown() {
		shutdown = true;
	}
}

 

工作任务接口：

 

<SPAN style="COLOR: #3366ff">/**
 * Task.java
 *
 */

/**
 * The task want to execute.
 *
 * @author  gray
 * @version 1.0
 */
public interface Task {

    public void execute();
}</SPAN>

/**
 * Task.java
 *
 */

/**
 * The task want to execute.
 * 
 * @author  gray
 * @version 1.0
 */
public interface Task {

	public void execute();
}

 

工作任务类：

<SPAN style="COLOR: #3366ff">/**
 * SimpleTask.java
 *
 */

/**
 * @author  gray
 * @version 1.0
 */
public class SimpleTask implements Task {

    /* (non-Javadoc)
     * @see Task#execute()
     */
    public void execute() {
        System.out.println(Thread.currentThread());
    }

}</SPAN>

/**
 * SimpleTask.java
 *
 */

/**
 * @author  gray
 * @version 1.0
 */
public class SimpleTask implements Task {

	/* (non-Javadoc)
	 * @see Task#execute()
	 */
	public void execute() {
		System.out.println(Thread.currentThread());
	}

}

 

线程池测试类：

<SPAN style="COLOR: #3366ff">/**
 * ThreadPoolDemo.java
 *
 */

/**
 * @author  gray
 * @version 1.0
 */
public class ThreadPoolDemo {

    public static void main(String[] args) {
        ThreadPoolManager threadMg = new ThreadPoolManager();

        for(int i = 0; i < 50; i++) {
            threadMg.addTask(new SimpleTask());
        }
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        threadMg.shutdown();
    }
}</SPAN>