Java线程池深入理解

最近项目中进行告警模块性能优化，不少地方使用了线程池技术，整理总结如下。

package com.coshaho.threadpool;import java.util.concurrent.BlockingQueue; import java.util.concurrent.Executors; import java.util.concurrent.RejectedExecutionHandler; import java.util.concurrent.ThreadFactory; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit;/*** 线程池学习* @author coshaho*/ public class MyThreadPool {/*** 第一章 线程池初始化*/// 核心线程数量private int corePoolSize;// 最大线程数量private int maximumPoolSize;// 空闲线程存活时间private long keepAliveTime;// 空闲线程存活时间单位private TimeUnit unit;// 线程阻塞队列private BlockingQueue<Runnable> workQueue;/*** 线程创建工厂，一般自定义，用于封装传入ThreadPool的Runnable任务* 默认：Executors.defaultThreadFactory()* public interface ThreadFactory { * Thread newThread(Runnable r); * }*/private ThreadFactory threadFactory;// 线程拒绝机制private RejectedExecutionHandler handler;public void initThreadPoolExecutor(){ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit,workQueue,threadFactory,handler);// 设置线程池核心线程数executor.setCorePoolSize(corePoolSize);// 设置线程池最大线程数executor.setMaximumPoolSize(maximumPoolSize);// 初始化一个核心线程executor.prestartCoreThread();// 初始化所有核心线程executor.prestartAllCoreThreads();// 不会立即终止线程池，而是要等所有任务缓存队列中的任务都执行完后才终止，但再也不会接受新的任务executor.shutdown();// 立即终止线程池，尝试打断正在执行的任务，并且清空任务缓存队列，返回尚未执行的任务executor.shutdownNow();}/*** 第二章 线程池任务处理机制* 来了一个任务后的处理机制* 1、 当线程池线程数量小于corePoolSize时，立即新建一个线程执行任务；* 2、 当线程池线程数量等于corePoolSize，workQueue不满时，任务入workQueue队列，等待调度；* 3、 当workQueue满，线程池线程数量小于maximumPoolSize时，新建线程执行任务；* 4、 当线程池线程数量等于maximumPoolSize，workQueue满时，采用线程拒绝机制处理任务。*//*** 第三章 线程阻塞队列* workQueue的类型为BlockingQueue<Runnable>，通常可以取下面三种类型：* 1、ArrayBlockingQueue：基于数组的先进先出队列，此队列创建时必须指定大小；* 2、LinkedBlockingQueue：基于链表的先进先出队列，如果创建时没有指定此队列大小，则默认为Integer.MAX_VALUE；* 3、synchronousQueue：这个队列比较特殊，它不会保存提交的任务，而是将直接新建一个线程来执行新来的任务。*//*** 第四章 线程拒绝机制*/public void rejectedExecutionHandlerLearn(){// 丢弃任务并抛出RejectedExecutionException异常handler = new ThreadPoolExecutor.AbortPolicy();// 也是丢弃任务，但是不抛出异常handler = new ThreadPoolExecutor.DiscardPolicy();// 丢弃队列最前面的任务，然后重新尝试执行任务（重复此过程）handler = new ThreadPoolExecutor.DiscardOldestPolicy();// 由调用线程处理该任务 handler = new ThreadPoolExecutor.CallerRunsPolicy();}/*** 第五章 JDK默认线程池*/public void jdkThreadPool(){//创建一个缓冲池，缓冲池容量大小为Integer.MAX_VALUEExecutors.newCachedThreadPool(); //创建容量为1的缓冲池Executors.newSingleThreadExecutor();//创建固定容量大小的缓冲池 Executors.newFixedThreadPool(5); }/**public static ExecutorService newFixedThreadPool(int nThreads) {return new ThreadPoolExecutor(nThreads, nThreads,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());}public static ExecutorService newSingleThreadExecutor() {return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>()));}public static ExecutorService newCachedThreadPool() {return new ThreadPoolExecutor(0, Integer.MAX_VALUE,60L, TimeUnit.SECONDS,new SynchronousQueue<Runnable>());}*//*** 第六章 线程池大小设置* 1、 如果是CPU密集型任务，就需要尽量压榨CPU，参考值可以设为 NCPU+1；* 2、 如果是IO密集型任务，参考值可以设置为2*NCPU。*//*** 第七章 JDK源码* Creates a new {@code ThreadPoolExecutor} with the given initial* parameters.** @param corePoolSize the number of threads to keep in the pool, even* if they are idle, unless {@code allowCoreThreadTimeOut} is set* @param maximumPoolSize the maximum number of threads to allow in the* pool* @param keepAliveTime when the number of threads is greater than* the core, this is the maximum time that excess idle threads* will wait for new tasks before terminating.* @param unit the time unit for the {@code keepAliveTime} argument* @param workQueue the queue to use for holding tasks before they are* executed. This queue will hold only the {@code Runnable}* tasks submitted by the {@code execute} method.* @param threadFactory the factory to use when the executor* creates a new thread* @param handler the handler to use when execution is blocked* because the thread bounds and queue capacities are reached* @throws IllegalArgumentException if one of the following holds:<br>* {@code corePoolSize < 0}<br>* {@code keepAliveTime < 0}<br>* {@code maximumPoolSize <= 0}<br>* {@code maximumPoolSize < corePoolSize}* @throws NullPointerException if {@code workQueue}* or {@code threadFactory} or {@code handler} is nullpublic ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler)*/ }

 

转载于:https://www.cnblogs.com/coshaho/p/5426887.html

总结

以上是生活随笔为你收集整理的Java线程池深入理解的全部内容，希望文章能够帮你解决所遇到的问题。

如果觉得生活随笔网站内容还不错，欢迎将生活随笔推荐给好友。