Executors框架成员：
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<Runnable> workQueue) { ????????this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, ?????????????Executors.defaultThreadFactory(), defaultHandler); ????} ??? public ThreadPoolExecutor(int corePoolSize, ??????????????????????????????int maximumPoolSize, ??????????????????????????????long keepAliveTime, ??????????????????????????????TimeUnit unit, ??????????????????????????????BlockingQueue<Runnable> 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<Runnable> 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<Runnable>()); } public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) { ????????return new ThreadPoolExecutor(nThreads, nThreads, ??????????????????????????????????????0L, TimeUnit.MILLISECONDS, ??????????????????????????????????????new LinkedBlockingQueue<Runnable>(), ??????????????????????????????????????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<Runnable>())); } ????public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) { ????????return new FinalizableDelegatedExecutorService ????????????(new ThreadPoolExecutor(1, 1, ????????????????????????????????????0L, TimeUnit.MILLISECONDS, ????????????????????????????????????new LinkedBlockingQueue<Runnable>(), ????????????????????????????????????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<Runnable>()); } ????public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) { ????????return new ThreadPoolExecutor(0, Integer.MAX_VALUE, ??????????????????????????????????????60L, TimeUnit.SECONDS, ??????????????????????????????????????new SynchronousQueue<Runnable>(), ??????????????????????????????????????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