Java并发编程系列23:Executors框架和ThreadPoolExecutor实现类了解

ThreadPoolExecutor实现类、ScheduledThreadPoolExecutor实现类、Future接口、Runnable接口、Callable接口和Executors。

java.util.concurrent.Executor : 负责线程的使用与调度的根接口 
　|–ExecutorService：Executor的子接口，线程池的主要接口 
　　　|–ThreadPoolExecutor：ExecutorService的实现类 
　　　|–ScheduledExecutorService：ExecutorService的子接口，负责线程的调度 
　　　　　|–ScheduledThreadPoolExecutor：既继承了ThreadPoolExecutor，同时实现了ScheduledExecutorService

ThreadPoolExecutor实现类了解:

构造方法:

    public ThreadPoolExecutor(int corePoolSize,

                              int maximumPoolSize,

                              long keepAliveTime,

                              TimeUnit unit,

                              BlockingQueue workQueue) {

        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,

             Executors.defaultThreadFactory(), defaultHandler);

    }    

public ThreadPoolExecutor(int corePoolSize,

                              int maximumPoolSize,

                              long keepAliveTime,

                              TimeUnit unit,

                              BlockingQueue workQueue,

                              ThreadFactory threadFactory) {

        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,

             threadFactory, defaultHandler);

    }

参数介绍:

int corePoolSize, 核心线程大小int maximumPoolSize,最大线程大小long keepAliveTime, 超过corePoolSize的线程多久不活动被销毁时间TimeUnit unit,时间单位BlockingQueue workQueue 任务队列ThreadFactory threadFactory 线程池工厂RejectedExecutionHandler handler 拒绝策略

以下介绍三种类型的ThreadPoolExecutor：SingleThreadExecutor、FixedThreadPool和CachedThreadPool。

这3种线程池都是创建了ThreadPollExecutor对象，只是传递的参数不一样，传入的workQueue 都是默认，即最大可添加Integer.MAX_VALUE个任务，这也就是阿里巴巴java开发规范禁止直接使用java提供的默认线程池的原因。

参考：https://blog.csdn.net/weixin_41888813/article/details/90769126

1、FixedThreadPool

线程数量固定的线程池(定长线程池)，可控制线程最大并发数，超出的线程会在队列中等待。

它适用于为了满足资源管理的需求，而需要限制当前线程数量的应用场景，它适用于负载比较重的服务器。

    public static ExecutorService newFixedThreadPool(int nThreads) {

        return new ThreadPoolExecutor(nThreads, nThreads,

                                      0L, TimeUnit.MILLISECONDS,

                                      new linkedBlockingQueue());

}

public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {

        return new ThreadPoolExecutor(nThreads, nThreads,

                                      0L, TimeUnit.MILLISECONDS,

                                      new linkedBlockingQueue(),

                                      threadFactory);

}

初始线程数为：nThreads最大线程数为：nThreads超时时间为：0毫秒阻塞队列采用的是：linkedBlockingQueue

线程池最大线程数量maxmumPoolSize和核心线程池的数量corePoolSize设置为相等，使用LinkedBlockingQueue作为阻塞队列。

2、SingleThreadExecutor

只有一个线程的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。

它适用于需要保证顺序地执行各个任务；并且在任意时间点，不会有多个线程是活动的应用场景。

    public static ExecutorService newSingleThreadExecutor() {

        return new FinalizableDelegatedExecutorService

            (new ThreadPoolExecutor(1, 1,

                                    0L, TimeUnit.MILLISECONDS,

                                    new linkedBlockingQueue()));

}

    public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {

        return new FinalizableDelegatedExecutorService

            (new ThreadPoolExecutor(1, 1,

                                    0L, TimeUnit.MILLISECONDS,

                                    new linkedBlockingQueue(),

                                    threadFactory));

    }

初始线程数为：1最大线程数为：1超时时间为：0毫秒阻塞队列采用的是：linkedBlockingQueue

3、newCachedThreadPool

一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。

它适用于执行很多的短期异步任务的小程序，或者是负载较轻的服务器。

    public static ExecutorService newCachedThreadPool() {

        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,

                                      60L, TimeUnit.SECONDS,

                                      new SynchronousQueue());

}

    public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {

        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,

                                      60L, TimeUnit.SECONDS,

                                      new SynchronousQueue(),

                                      threadFactory);

    }

初始线程数为：0最大线程数为： Integer.MAX_VALUE(int的最大值)超时时间为：1分钟阻塞队列采用的是：SynchronousQueue

参考：https://www.cnblogs.com/xiondun/p/14764096.html

参考：https://blog.csdn.net/tongdanping/article/details/79625109

参考：https://blog.csdn.net/qq_43040688/category_9910156.html

参考：https://blog.csdn.net/qq_43040688/article/details/106046629

参考：关于阿里规范禁止使用Executors创建线程池的分析