java编程实战

线程池为什么要有它：

线程创建要开辟虚拟机栈，释放线程要垃圾回收的。

server端要并发访问数据库的。

服务器启动有线程池放着。

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线程池的概念：

1.任务队列

2.拒绝策略(抛出异常，直接丢弃，阻塞，放在临时队列)

3.初始化值init(min),初始线程池大小

3.active

5.max线程池线程的最大个数

min<=active<=max

quartz:定时任务

代码：

package chapter13;

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

public class SimpleThreadPoolMy {

private final int size;

private final static int DEFAULT_SIZE = 10;

private static volatile int seq = 0;

private final static String THREAD_PREFIX = "SIMPLE_THREAD_POOL-";

private final static ThreadGroup GROUP = new ThreadGroup("Pool_Group");

private final static List<WorkerTask> THREAD_QUEUE = new ArrayList<>();

/**

* task queue

*/

private final static LinkedList<Runnable> TASK_QUEUE = new LinkedList<>();

public SimpleThreadPoolMy() {

this(DEFAULT_SIZE);

}

public SimpleThreadPoolMy(int size) {

this.size = size;

init();

}

private void init() {

for (int i = 0; i < size; i++) {

createWorkTask();

}

}

private void createWorkTask() {

WorkerTask task = new WorkerTask(GROUP, THREAD_PREFIX + (seq++));

task.start();

THREAD_QUEUE.add(task);

}

private enum TaskState {

FREE, RUNNING, BLOCKEED, DEAD

}

public void submit(Runnable runnable) {

synchronized (TASK_QUEUE) {//别的方法有读的操作，这里有写的操作，所以你要加锁的

TASK_QUEUE.addLast(runnable);

TASK_QUEUE.notifyAll();

}

}

/**

* Thread in ThreadPool

*/

private static class WorkerTask extends Thread {//为什么定义为private呢就是为了不想让别人知道我是什么

private volatile TaskState taskState = TaskState.FREE;

public WorkerTask(ThreadGroup group, String name) {//构造方法，调用了Thread的构造

super(group, name);

}

public TaskState getTaskState() {

return this.taskState;

}

public void close() {

this.taskState = TaskState.DEAD;

}

public void run() {//重写外汇返佣保证执行完之后不能挂掉

OUTER:

while (this.taskState != TaskState.DEAD) {//当前的线程没有死掉

Runnable runnable;

synchronized (TASK_QUEUE) {//去任务队列调取任务

while (TASK_QUEUE.isEmpty()) {

try {

taskState = TaskState.BLOCKEED;

TASK_QUEUE.wait();//没有任务就释放锁，这个线程在TASK_QUEUE上等待 wait会被打断  打断的话就break出来

} catch (InterruptedException e) {

break OUTER;//https://blog.csdn.net/zhaoheng2017/article/details/78385973  被打断了就接着去调取任务

}

}

runnable = TASK_QUEUE.removeFirst();//队列 先进先出 任务队列只被消费一次 比如数据库线程池，取出来我执行连接就可以了

}

if (runnable != null) {

taskState = TaskState.RUNNING;

runnable.run();

taskState = TaskState.FREE;

}

}

}

}

}

原文链接：https://blog.csdn.net/qq_28764557/article/details/103575987