线程池（一）

1. Java代码
  1. public ThreadPoolExecutor(int corePoolSize,
  2. int maximumPoolSize,
  3. long keepAliveTime,
  4. TimeUnit unit,
  5. BlockingQueue<Runnable> workQueue,
  6. ThreadFactory threadFactory,
  7. RejectedExecutionHandler handler) {
  8. if (corePoolSize < 0 ||
  9. maximumPoolSize <= 0 ||
  10. maximumPoolSize < corePoolSize ||
  11. keepAliveTime < 0)
  12. throw new IllegalArgumentException();
  13. if (workQueue == null || threadFactory == null || handler == null)
  14. throw new NullPointerException();
  15. this.corePoolSize = corePoolSize;
  16. this.maximumPoolSize = maximumPoolSize;
  17. this.workQueue = workQueue;
  18. this.keepAliveTime = unit.toNanos(keepAliveTime);
  19. this.threadFactory = threadFactory;
  20. this.handler = handler;
  21. }

构造方法参数讲解

参数名	作用
corePoolSize	队列未满时，线程最大并发数；核心线程池大小如：80
maximumPoolSize	队列满后线程能够到达的最大并发数；最大线程池大小如：100
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大于80剩余线程存活的时间
TimeUnit	keepAliveTime时间单位大于80剩余线程存活的时间
workQueue	阻塞任务队列：大于80之后进入该queue 如corePoolSize=5 实际有10个线程，超出的5个将会存放到待队列里
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；如maxmumPoolSize=5，workQueue的size=2，实际最大线程为10>7超出的3个线程将会提交给RejectedExecutionHandler

代码演示：

public class RejectedExecutionHandlerAction implements RejectedExecutionHandler {
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        executor.allowCoreThreadTimeOut(true);
        System.out.println("aaa"+ executor.getActiveCount());
    }
}
 public void test() throws InterruptedException {
        //队列不限定长度 无论实际有多少个线程都不会触发 RejectedExecutionHandler
        LinkedBlockingDeque linkedBlockingDeque = new LinkedBlockingDeque();
        RejectedExecutionHandlerAction action = new RejectedExecutionHandlerAction();
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 5, 5, TimeUnit.SECONDS, linkedBlockingDeque, action );
        for (int i = 0; i < 10; i++) {
            threadPoolExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    System.out.println(" 线程名称：" + Thread.currentThread().getName() + "在" + System.currentTimeMillis() + "进入printA");
                }
            });
        }
        System.out.println(linkedBlockingDeque.size());
        Thread.sleep(20000);
        System.out.println(linkedBlockingDeque.size());
    }

运行结果：

指定队列长度，超出线程触发RejectedExecutionHandler

LinkedBlockingDeque linkedBlockingDeque = new LinkedBlockingDeque(2);

corePoolSize，maximumPoolSize，workQueue之间关系。
1. 当线程池中线程数小于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. 当线程池中线程数达到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workQueue已满，且提交任务数超过maximumPoolSize，任务由RejectedExecutionHandler处理。
5. 当线程池中线程数超过corePoolSize，且超过这部分的空闲时间达到keepAliveTime时，回收这些线程。
6. 当设置allowCoreThreadTimeOut(true)时，线程池中corePoolSize范围内的线程空闲时间达到keepAliveTime也将回收。
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

Java代码

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

Java代码

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

Java代码

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

Java代码

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);
}