[笔记]Executors框架

框架结构

• 任务：Runnable和Callable
• 任务的执行：Executor接口->ExecutorService接口
  
  • ThreadPoolExecutor
  • ScheduledThreadPoolExecutor
• 异步计算的结果：Future接口->FutureTask类

ThreadPoolExecutor

new ThreadPoolExecutor(corePoolSize,maximumPoolSize,keepAliveTime,timeunit,runnableTaskQueue,handler)

• corePoolSize: 预热到这个线程大小，不再创建新线程，就要放到runnableTaskQueue里面
• maximumPoolSize：只有runnableTaskQueue满了，才会创建新线程，最大线程数不超过这个值
• runnableTaskQueue： 任务队列
• handler：饱和策略
  
  • AbortPolicy：直接抛弃

通常使用工厂类Executors创建：

1.FixedThreadPool：满足资源管理的需求，适合负载比较重的服务器

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

源代码：

public static 

2.SingleThreadPool: 满足保证顺序的执行每个任务，并且在任意时间点，不会有多个线程是活动的场景

public static ExecutorService newSingleThreadPool()public static ExecutorService newSingleThreadPool(ThreadFactory threadFactory)

3.CachedThreadPool:大小无界，适用于很多短期异步的小程序，或者是负载较轻的服务器

public static ExecutorService newCachedThreadPool()public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory)

ScheduledThreadPoolExecutor

使用工厂类Executors创建
1.ScheduledThreadPoolExecutor:

public static ExecutorService newScheduledThreadPool(int nThreads)public static ExecutorService newScheduledThreadPool(int nThreads,ThreadFactory threadFactory)

2.SingleThreadScheduledExecutor:

public static ExecutorService newSingleThreadScheduledExecutor()public static ExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory)

Future接口

当我们把Runnable接口或者Callable接口submit给ThreadPoolExecutor时，会返回一个FutureTask对象，API：

<T> Future<T> submit(Callable<T> Task)<T> Future<T> submit(Runnable Task,T result)Future<?> submit(Runnable Task)

Runnable和Callable接口

Executors提供的：

public static Callable<Object> callable(Runnable task)public static <T>Callable<T> callable(Runnable task,T Result)