ThreadPoolExecutor的参数理解
一、使用Executors创建线程池
之前创建线程的时候都是用的Executors的newFixedThreadPool(),newSingleThreadExecutor(),newCachedThreadPool()这三个方法。
1. newFixedThreadPool()
创建线程数固定大小的线程池。
2.newSingleThreadPool()
创建线程数为1的线程池,
3.newCachedThreadPool()
创建可缓冲的线程池。没有大小限制
二、使用ThreadPoolExecutor创建线程池
ThreadPoolExecutor的构造函数
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { if (corePoolSize < 0 || maximumPoolSize <= 0 || maximumPoolSize < corePoolSize || keepAliveTime < 0) throw new IllegalArgumentException(); if (workQueue == null || threadFactory == null || handler == null) throw new NullPointerException(); this.corePoolSize = corePoolSize; this.maximumPoolSize = maximumPoolSize; this.workQueue = workQueue; this.keepAliveTime = unit.toNanos(keepAliveTime); this.threadFactory = threadFactory; this.handler = handler; }
参数:
1、corePoolSize核心线程数大小,当线程数<corePoolSize ,会创建线程执行runnable
2、maximumPoolSize 最大线程数, 当线程数 >= corePoolSize的时候,会把runnable放入workQueue中
3、keepAliveTime 保持存活时间,当线程数大于corePoolSize的空闲线程能保持的最大时间。
4、unit 时间单位
5、workQueue 保存任务的阻塞队列
6、threadFactory 创建线程的工厂
7、handler 拒绝策略
任务执行顺序:
1、当线程数小于corePoolSize时,创建线程执行任务。
2、当线程数大于等于corePoolSize并且workQueue没有满时,放入workQueue中
3、线程数大于等于corePoolSize并且当workQueue满时,新任务新建线程运行,线程总数要小于maximumPoolSize
4、当线程总数等于maximumPoolSize并且workQueue满了的时候执行handler的rejectedExecution。也就是拒绝策略。
ThreadPoolExecutor默认有四个拒绝策略:
1、ThreadPoolExecutor.AbortPolicy() 直接抛出异常RejectedExecutionException
2、ThreadPoolExecutor.CallerRunsPolicy() 直接调用run方法并且阻塞执行
3、ThreadPoolExecutor.DiscardPolicy() 直接丢弃后来的任务
4、ThreadPoolExecutor.DiscardOldestPolicy() 丢弃在队列中队首的任务
当然可以自己继承RejectedExecutionHandler来写拒绝策略.
int corePoolSize = 1; int maximumPoolSize = 2; int keepAliveTime = 10; // BlockingQueue<Runnable> workQueue = new LinkedBlockingQueue<Runnable>(); BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>(5); ThreadFactory threadFactory = Executors.defaultThreadFactory(); //线程池和队列满了之后的处理方式 //1.跑出异常 RejectedExecutionHandler handler = new ThreadPoolExecutor.AbortPolicy(); RejectedExecutionHandler handler2 = new ThreadPoolExecutor.CallerRunsPolicy(); RejectedExecutionHandler handler3 = new ThreadPoolExecutor.DiscardPolicy(); RejectedExecutionHandler handler4 = new ThreadPoolExecutor.DiscardOldestPolicy(); ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, workQueue, threadFactory, handler2); for (int j = 1; j < 15; j++) { threadPoolExecutor.execute(new Runnable() { public void run() { try { System.out.println(Thread.currentThread().getName()); TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } } }); } System.out.println(threadPoolExecutor); }