一、核心构造方法讲解
| 参数名 | 作用 |
| corePoolSize | 核心线程池大小 |
| maximumPoolSize | 最大线程池大小 |
| keepAliveTime | 线程池中超过corePoolSize数目的空闲线程最大存活时间；可以allowCoreThreadTimeOut(true)使得核心线程有效时间 |
| TimeUnit | keepAliveTime时间单位 |
| workQueue | 阻塞任务队列 |
| threadFactory | 新建线程工厂 |
| RejectedExecutionHandler | 当提交任务数超过maxmumPoolSize+workQueue之和时，任务会交给RejectedExecutionHandler来处理 |
其中比较容易让人误解的是：corePoolSize，maximumPoolSize，workQueue之间关系。
1.当线程池小于corePoolSize时，新提交任务将创建一个新线程执行任务，即使此时线程池中存在空闲线程。
2.当线程池达到corePoolSize时，新提交任务将被放入workQueue中，等待线程池中任务调度执行
3.当workQueue已满，且maximumPoolSize>corePoolSize时，新提交任务会创建新线程执行任务
4.当提交任务数超过maximumPoolSize时，新提交任务由RejectedExecutionHandler处理
5.当线程池中超过corePoolSize线程，空闲时间达到keepAliveTime时，关闭空闲线程
6.当设置allowCoreThreadTimeOut(true)时，线程池中corePoolSize线程空闲时间达到keepAliveTime也将关闭
二、线程管理机制图示：
三、Executors提供的线程池配置方案
1、构造一个固定线程数目的线程池，配置的corePoolSize与maximumPoolSize大小相同，同时使用了一个无界LinkedBlockingQueue存放阻塞任务，因此多余的任务将存在再阻塞队列，不会由RejectedExecutionHandler处理
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
2、构造一个缓冲功能的线程池，配置corePoolSize=0，maximumPoolSize=Integer.MAX_VALUE，keepAliveTime=60s,以及一个无容量的阻塞队列 SynchronousQueue，因此任务提交之后，将会创建新的线程执行；线程空闲超过60s将会销毁
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
3、构造一个只支持一个线程的线程池，配置corePoolSize=maximumPoolSize=1，无界阻塞队列LinkedBlockingQueue；保证任务由一个线程串行执行
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
4、构造有定时功能的线程池，配置corePoolSize，无界延迟阻塞队列DelayedWorkQueue；有意思的是：maximumPoolSize=Integer.MAX_VALUE，由于DelayedWorkQueue是无界队列，所以这个值是没有意义的
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
return new ScheduledThreadPoolExecutor(corePoolSize);
}
public static ScheduledExecutorService newScheduledThreadPool(
int corePoolSize, ThreadFactory threadFactory) {
return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}
public ScheduledThreadPoolExecutor(int corePoolSize,
ThreadFactory threadFactory) {
super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,
new DelayedWorkQueue(), threadFactory);
}
四、定制属于自己的非阻塞线程池
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class CustomThreadPoolExecutor {
private ThreadPoolExecutor pool = null;
/**
* 线程池初始化方法
*
* corePoolSize 核心线程池大小----10
* maximumPoolSize 最大线程池大小----30
* keepAliveTime 线程池中超过corePoolSize数目的空闲线程最大存活时间----30+单位TimeUnit
* TimeUnit keepAliveTime时间单位----TimeUnit.MINUTES
* workQueue 阻塞队列----new ArrayBlockingQueue<Runnable>(10)====10容量的阻塞队列
* threadFactory 新建线程工厂----new CustomThreadFactory()====定制的线程工厂
* rejectedExecutionHandler 当提交任务数超过maxmumPoolSize+workQueue之和时,
* 即当提交第41个任务时(前面线程都没有执行完,此测试方法中用sleep(100)),
* 任务会交给RejectedExecutionHandler来处理
*/
public void init() {
pool = new ThreadPoolExecutor(
10,
30,
30,
TimeUnit.MINUTES,
new ArrayBlockingQueue<Runnable>(10),
new CustomThreadFactory(),
new CustomRejectedExecutionHandler());
}
public void destory() {
if(pool != null) {
pool.shutdownNow();
}
}
public ExecutorService getCustomThreadPoolExecutor() {
return this.pool;
}
private class CustomThreadFactory implements ThreadFactory {
private AtomicInteger count = new AtomicInteger(0);
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
String threadName = CustomThreadPoolExecutor.class.getSimpleName() + count.addAndGet(1);
System.out.println(threadName);
t.setName(threadName);
return t;
}
}
private class CustomRejectedExecutionHandler implements RejectedExecutionHandler {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
// 记录异常
// 报警处理等
System.out.println("error.............");
}
}
// 测试构造的线程池
public static void main(String[] args) {
CustomThreadPoolExecutor exec = new CustomThreadPoolExecutor();
// 1.初始化
exec.init();
ExecutorService pool = exec.getCustomThreadPoolExecutor();
for(int i=1; i<100; i++) {
System.out.println("提交第" + i + "个任务!");
pool.execute(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("running=====");
}
});
}
// 2.销毁----此处不能销毁,因为任务没有提交执行完,如果销毁线程池,任务也就无法执行了
// exec.destory();
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
