ThreadPoolExecutor機制?
一、概述?
1、ThreadPoolExecutor作為java.util.concurrent包對外提供基礎實現，以內部線程池的形式對外提供管理任務執行，線程調度，線程池管理等等服務；?
2、Executors方法提供的線程服務，都是通過參數設置來實現不同的線程池機制。?
3、先來了解其線程池管理的機制，有助于正確使用，避免錯誤使用導致嚴重故障。同時可以根據自己的需求實現自己的線程池?

二、核心構造方法講解?
下面是ThreadPoolExecutor最核心的構造方法?

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;}

構造方法參數講解?

參數名	作用
corePoolSize	核心線程池大小
maximumPoolSize	最大線程池大小
keepAliveTime	線程池中超過corePoolSize數目的空閑線程最大存活時間；可以allowCoreThreadTimeOut(true)使得核心線程有效時間
TimeUnit	keepAliveTime時間單位
workQueue	阻塞任務隊列
threadFactory	新建線程工廠
RejectedExecutionHandler	當提交任務數超過maxmumPoolSize+workQueue之和時，任務會交給RejectedExecutionHandler來處理

重點講解：?
其中比較容易讓人誤解的是：corePoolSize，maximumPoolSize，workQueue之間關系。?

1.當線程池小于corePoolSize時，新提交任務將創建一個新線程執行任務，即使此時線程池中存在空閑線程。?
2.當線程池達到corePoolSize時，新提交任務將被放入workQueue中，等待線程池中任務調度執行?
3.當workQueue已滿，且maximumPoolSize>corePoolSize時，新提交任務會創建新線程執行任務?
4.當提交任務數超過maximumPoolSize時，新提交任務由RejectedExecutionHandler處理?
5.當線程池中超過corePoolSize線程，空閑時間達到keepAliveTime時，關閉空閑線程?
6.當設置allowCoreThreadTimeOut(true)時，線程池中corePoolSize線程空閑時間達到keepAliveTime也將關閉?

線程管理機制圖示：?


三、Executors提供的線程池配置方案?

1、構造一個固定線程數目的線程池，配置的corePoolSize與maximumPoolSize大小相同，同時使用了一個無界LinkedBlockingQueue存放阻塞任務，因此多余的任務將存在再阻塞隊列，不會由RejectedExecutionHandler處理?

public static ExecutorService newFixedThreadPool(int nThreads) {return new ThreadPoolExecutor(nThreads, nThreads,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());}

2、構造一個緩沖功能的線程池，配置corePoolSize=0，maximumPoolSize=Integer.MAX_VALUE，keepAliveTime=60s,以及一個無容量的阻塞隊列 SynchronousQueue，因此任務提交之后，將會創建新的線程執行；線程空閑超過60s將會銷毀?

public static ExecutorService newCachedThreadPool() {return new ThreadPoolExecutor(0, Integer.MAX_VALUE,60L, TimeUnit.SECONDS,new SynchronousQueue<Runnable>());}

3、構造一個只支持一個線程的線程池，配置corePoolSize=maximumPoolSize=1，無界阻塞隊列LinkedBlockingQueue；保證任務由一個線程串行執行?

public static ExecutorService newSingleThreadExecutor() {return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>()));}

4、構造有定時功能的線程池，配置corePoolSize，無界延遲阻塞隊列DelayedWorkQueue；有意思的是：maximumPoolSize=Integer.MAX_VALUE，由于DelayedWorkQueue是無界隊列，所以這個值是沒有意義的?

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {return new ScheduledThreadPoolExecutor(corePoolSize);}public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory) {return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);}public ScheduledThreadPoolExecutor(int corePoolSize,ThreadFactory threadFactory) {super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,new DelayedWorkQueue(), threadFactory);}

四、定制屬于自己的線程池?

import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.ExecutorService; import java.util.concurrent.RejectedExecutionHandler; import java.util.concurrent.ThreadFactory; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicInteger;public class CustomThreadPoolExecutor {private ThreadPoolExecutor pool = null;/*** 線程池初始化方法* * corePoolSize 核心線程池大小----10* maximumPoolSize 最大線程池大小----30* keepAliveTime 線程池中超過corePoolSize數目的空閑線程最大存活時間----30+單位TimeUnit* TimeUnit keepAliveTime時間單位----TimeUnit.MINUTES* workQueue 阻塞隊列----new ArrayBlockingQueue<Runnable>(10)====10容量的阻塞隊列* threadFactory 新建線程工廠----new CustomThreadFactory()====定制的線程工廠* rejectedExecutionHandler 當提交任務數超過maxmumPoolSize+workQueue之和時,* 即當提交第41個任務時(前面線程都沒有執行完,此測試方法中用sleep(100)),* 任務會交給RejectedExecutionHandler來處理*/public void init() {pool = new ThreadPoolExecutor(10,30,30,TimeUnit.MINUTES,new ArrayBlockingQueue<Runnable>(10),new CustomThreadFactory(),new CustomRejectedExecutionHandler());}public void destory() {if(pool != null) {pool.shutdownNow();}}public ExecutorService getCustomThreadPoolExecutor() {return this.pool;}private class CustomThreadFactory implements ThreadFactory {private AtomicInteger count = new AtomicInteger(0);@Overridepublic Thread newThread(Runnable r) {Thread t = new Thread(r);String threadName = CustomThreadPoolExecutor.class.getSimpleName() + count.addAndGet(1);System.out.println(threadName);t.setName(threadName);return t;}}private class CustomRejectedExecutionHandler implements RejectedExecutionHandler {@Overridepublic void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {// 記錄異常// 報警處理等System.out.println("error.............");}}// 測試構造的線程池public static void main(String[] args) {CustomThreadPoolExecutor exec = new CustomThreadPoolExecutor();// 1.初始化 exec.init();ExecutorService pool = exec.getCustomThreadPoolExecutor();for(int i=1; i<100; i++) {System.out.println("提交第" + i + "個任務!");pool.execute(new Runnable() {@Overridepublic void run() {try {Thread.sleep(300);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("running=====");}});}// 2.銷毀----此處不能銷毀,因為任務沒有提交執行完,如果銷毀線程池,任務也就無法執行了// exec.destory();try {Thread.sleep(10000);} catch (InterruptedException e) {e.printStackTrace();}} }

方法中建立一個核心線程數為30個，緩沖隊列有10個的線程池。每個線程任務，執行時會先睡眠0.1秒，保證提交40個任務時沒有任務被執行完，這樣提交第41個任務是，會交給CustomRejectedExecutionHandler 類來處理。

http://825635381.iteye.com/blog/2184680

?

?

?

?

?

轉載于:https://www.cnblogs.com/softidea/p/4286051.html

總結

以上是生活随笔為你收集整理的JAVA进阶----ThreadPoolExecutor机制（转）的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。