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_VALUE
Executors.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 null
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler)
*/
}