thread pool classes hierarchy
java thread pool class hierarchy
Executor (java.util.concurrent)
|---ExecutorService (java.util.concurrent)
|---AbstractExecutorService (java.util.concurrent)
| |---ForkJoinPool (java.util.concurrent)
| |---ThreadPoolExecutor (java.util.concurrent)
| | |---ScheduledThreadPoolExecutor (java.util.concurrent)
|---DelegatedExecutorService in Executors (java.util.concurrent)
|---ScheduledExecutorService (java.util.concurrent)
three thread pool interfaces
Executor, a simple interface that supports launching new tasks.
ExecutorService, a sub-interface of Executor, which adds features that help manage the life cycle, both of the
individual tasks and of the executor itself.
ScheduledExecutorService, a sub-interface of ExecutorService, supports future and/or periodic execution of tasks.
common thread pool implements
ThreadPoolExecutor是 thread pool 最常用的实现。一般通过Executors静态工厂方法来创建。
//Executors.newFixedThreadPool
//Executors.newCachedThreadPool
//Executors.newSingleThreadExecutor
//同样的，Executors 还提供了 ScheduledExecutorService 的工具方法
//Executors.newSingleThreadScheduledExecutor
/**
* corePoolSize - 保留存活的线程个数
* maximumPoolSize - 最大线程个数
* keepAliveTime - 线程数超过 corePoolSize 时，空闲线程存活时间
* unit - keepAliveTime 的单位，毫秒秒分等
* workQueue – 任务队列，只保存通过 execute() 方法提交的 Runnable 任务
* threadFactory – 给自己创建一个线程的工厂方法
* handler – 当线程池达到数量限制或者任务队列满了，对新任务提交的处理策略
*/
class ThreadPoolExecutor {
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {}
}
JDK 默认的拒绝策略 RejectedExecutionHandler 有：
/**
* ThreadPoolExecutor.AbortPolicy - 默认的 handler，抛出一个 RejectedExecutionException
* ThreadPoolExecutor.CallerRunsPolicy - 提交任务的线程自己执行这个任务
* ThreadPoolExecutor.DiscardPolicy - 抛弃这个任务
* ThreadPoolExecutor.DiscardOldestPolicy - 抛弃任务队列中最早提交上来的任务，然后尝试重新提交当前这个任务
*/
任务提交执行流程
fork/join 框架
fork/join和上面ThreadPoolExecutor的区别在于使用了任务窃取算法，工作线程完成自己的任务后可以从其他线程偷取任务，提高整体的任务效率.
核心是一个ForkJoinPool class 和一个扩展的AbstractExecutorService. 执行ForkJoinTask 任务。
在 JDK8 中有个java.util.Arrays.parallelSort()使用的就是 fork/join.