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這期內(nèi)容當(dāng)中小編將會(huì)給大家?guī)?lái)有關(guān)怎么在Java中使用線程工廠監(jiān)控線程池,文章內(nèi)容豐富且以專業(yè)的角度為大家分析和敘述,閱讀完這篇文章希望大家可以有所收獲。
線程池中的線程從哪里來(lái)呢?就是ThreadFoctory
public interface ThreadFactory { Thread newThread(Runnable r); }
Threadfactory里面有個(gè)接口,當(dāng)線程池中需要?jiǎng)?chuàng)建線程就會(huì)調(diào)用該方法,也可以自定義線程工廠
public class ThreadfactoryText { public static void main(String[] args) { Runnable runnable=new Runnable() { @Override public void run() { int num=new Random().nextInt(10); System.out.println(Thread.currentThread().getId()+"--"+System.currentTimeMillis()+"--睡眠"+num); try { TimeUnit.SECONDS.sleep(num); } catch (InterruptedException e) { e.printStackTrace(); } } }; //創(chuàng)建線程池 使用自定義線程工廠 采用默認(rèn)的拒絕策略 ExecutorService executorService=new ThreadPoolExecutor(5, 5, 0, TimeUnit.SECONDS, new SynchronousQueue<>(), new ThreadFactory() { @Override public Thread newThread(Runnable r) { Thread t=new Thread(r); t.setDaemon(true);//設(shè)置為守護(hù)線程,當(dāng)主線程運(yùn)行結(jié)束,線程池中線程也會(huì)被釋放 System.out.println("創(chuàng)建了線程"+t); return t; } }); //提交五個(gè)任務(wù) for (int i = 0; i < 5; i++) { executorService.submit(runnable); } } }
當(dāng)線程提交超過(guò)五個(gè)任務(wù)時(shí),線程池會(huì)默認(rèn)拋出異常
ThreadPoolExcutor提供了一組方法用于監(jiān)控線程池
int getActiveCount()//獲得線程池只當(dāng)前的獲得線程數(shù)量 long getCompletedTaskCount()//返回線程池完成任務(wù)數(shù)量 int getCorePoolSize()//線程池中核心任務(wù)數(shù)量 int getLargestPoolSize() //返回線程池中曾經(jīng)達(dá)到線程的最大數(shù) int getMaximumPoolSize()//返回線程池的最大容量 int getPoolSize()//返回線程大小 BlockingQueue<Runnable> getQueue()//返回阻塞隊(duì)列 long getTaskCount()//返回線程池收到任務(wù)總數(shù)
public class Text { public static void main(String[] args) throws InterruptedException { Runnable runnable = new Runnable() { @Override public void run() { System.out.println(Thread.currentThread().getId() + "線程開(kāi)始執(zhí)行--" + System.currentTimeMillis()); try { Thread.sleep(10000); } catch (InterruptedException e) { e.printStackTrace(); } } }; //創(chuàng)建線程池 使用默認(rèn)線程工廠 有界隊(duì)列 采用DiscardPolicy策略 ThreadPoolExecutor executorService = new ThreadPoolExecutor(2, 5, 0, TimeUnit.SECONDS, new ArrayBlockingQueue<>(5),Executors.defaultThreadFactory(),new ThreadPoolExecutor.DiscardPolicy()); //提交五個(gè)任務(wù) for (int i = 0; i < 30; i++) { executorService.submit(runnable); System.out.println("當(dāng)前線程核心線程數(shù)"+executorService.getCorePoolSize()+",最大線程數(shù):"+executorService.getMaximumPoolSize()+",當(dāng)前線程池大?。?quot;+executorService.getPoolSize()+"活動(dòng)線程數(shù):"+executorService.getActiveCount()+",收到任務(wù):"+executorService.getTaskCount()+"完成任務(wù)數(shù):"+executorService.getCompletedTaskCount()+"等待任務(wù)數(shù):"+executorService.getQueue().size()); TimeUnit.MILLISECONDS.sleep(500); } System.out.println("-------------------"); while (executorService.getActiveCount()>=0)//繼續(xù)對(duì)線程池進(jìn)行檢測(cè) { System.out.println("當(dāng)前線程核心線程數(shù)"+executorService.getCorePoolSize()+",最大線程數(shù):"+executorService.getMaximumPoolSize()+",當(dāng)前線程池大?。?quot;+executorService.getPoolSize()+"活動(dòng)線程數(shù):"+executorService.getActiveCount()+",收到任務(wù):"+executorService.getTaskCount()+"完成任務(wù)數(shù):"+executorService.getCompletedTaskCount()+"等待任務(wù)數(shù):"+executorService.getQueue().size()); Thread.sleep(1000);//每1秒檢測(cè)一次 } } }
當(dāng)線程池大小達(dá)到了核心線程數(shù),線程會(huì)被放在等待隊(duì)列。當(dāng)線程池等待隊(duì)列已滿會(huì)開(kāi)啟新的線程。當(dāng)當(dāng)前線程大小達(dá)到最大線程數(shù),等待隊(duì)列也滿了,再提交的話會(huì)執(zhí)行DiscardPolicy策略,直接丟棄這個(gè)無(wú)法處理的任務(wù),最后30個(gè)任務(wù)只剩下15個(gè)了。
原理如圖:
有時(shí)候需要對(duì)線程池進(jìn)行擴(kuò)展,如在監(jiān)控每個(gè)任務(wù)開(kāi)始和結(jié)束時(shí)間,或者自定義其他增強(qiáng)功能。
ThreadPoolExecutor線程池提供了兩個(gè)方法:
protected void beforeExecute(Thread t, Runnable r) { } protected void afterExecute(Runnable r, Throwable t) { }
線程池執(zhí)行某個(gè)任務(wù)前會(huì)執(zhí)行beforeExecute()方法,執(zhí)行后會(huì)調(diào)用afterExecute()方法
查看ThreadPoolExecutor源碼,在該類中定義了一個(gè)內(nèi)部類Worker,ThreadPoolExecutor線程池的工作線程就是Worker類的實(shí)例,Worker實(shí)例在執(zhí)行時(shí)會(huì)調(diào)用beforeExecute與afterExecute方法。
public void run() { runWorker(this); } final void runWorker(Worker w) { try { beforeExecute(wt, task); try { task.run(); afterExecute(task, null); } catch (Throwable ex) { afterExecute(task, ex); throw ex; } } finally { task = null; w.completedTasks++; w.unlock(); } } }
部分代碼已省略,線程執(zhí)行前會(huì)調(diào)用beforeExecute,執(zhí)行后會(huì)調(diào)用afterExecute方法。
package com; import java.util.concurrent.ExecutorService; import java.util.concurrent.LinkedBlockingDeque; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; public class Text07 { public static void main(String[] args) { //定義擴(kuò)展線程池 定義線程池類繼承ThreadPoolExecutor,然后重寫(xiě)其他方法 ExecutorService threadPoolExecutor= new ThreadPoolExecutor(5,5,0, TimeUnit.SECONDS,new LinkedBlockingDeque<>()){ //在內(nèi)部類重寫(xiě)開(kāi)始方法 @Override protected void beforeExecute(Thread t, Runnable r) { System.out.println(t.getId()+"線程準(zhǔn)備執(zhí)行任務(wù)"+((Mytask)r).name); } //在內(nèi)部類重寫(xiě)結(jié)束方法 @Override protected void afterExecute(Runnable r, Throwable t) { System.out.println(((Mytask)r).name+"執(zhí)行完成"); } //線程池退出 @Override protected void terminated() { System.out.println("線程池退出"); } }; for (int i = 0; i < 5; i++) { Mytask mytask=new Mytask("Thread"+i); threadPoolExecutor.execute(mytask); } } private static class Mytask implements Runnable { private String name; public Mytask(String name) { this.name=name; } @Override public void run() { System.out.println(name+"正在被執(zhí)行"+Thread.currentThread().getId()); try { Thread.sleep(1000);//模擬任務(wù)時(shí)長(zhǎng) } catch (InterruptedException e) { e.printStackTrace(); } } } }
線程池大小對(duì)系統(tǒng)性能有一定影響,過(guò)大或者過(guò)小都無(wú)法方法發(fā)揮系統(tǒng)最佳性能,不需要非常精確,只要避免極大或者極小就可以了,一般來(lái)說(shuō)線程池大小大姚考慮CPU數(shù)量
線程池大小=CPU數(shù)量 * 目標(biāo)CPU使用率*(1+等待時(shí)間與計(jì)算時(shí)間的比)
如果線程池執(zhí)行中,任務(wù)A在執(zhí)行過(guò)程中提交了任務(wù)B,任務(wù)B添加到線程池中的等待隊(duì)列,如果A的結(jié)束需要B的執(zhí)行結(jié)果,而B(niǎo)線程需要等待A線程執(zhí)行完畢,就可能會(huì)使其他所有工作線程都處于等待狀態(tài),待這些任務(wù)在阻塞隊(duì)列中執(zhí)行。線程池中沒(méi)有可以對(duì)阻塞隊(duì)列進(jìn)行處理的線程,就會(huì)一直等待下去照成死鎖。
適合給線程池提交相互獨(dú)立的任務(wù),而不是彼此依賴的任務(wù),對(duì)于彼此依賴的任務(wù),可以考慮分別提交給不同的線程池來(lái)處理。
import java.util.concurrent.ExecutorService; import java.util.concurrent.SynchronousQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; public class Text09 { public static void main(String[] args) { //創(chuàng)建線程池 ExecutorService executorService=new ThreadPoolExecutor(5,5,0, TimeUnit.SECONDS,new SynchronousQueue<>()); //向線程池中添加兩個(gè)數(shù)相處計(jì)算的任務(wù) for (int i = 0; i <5 ; i++) { executorService.submit(new Text(10,i)); } } private static class Text implements Runnable { private int x; private int y; public Text(int x,int y) { this.x=x; this.y=y; } @Override public void run() { System.out.println(Thread.currentThread().getName()+"線程x/y結(jié)果的為"+x+"/"+y+"="+(x/y)); } } }
可以看到只有四條結(jié)果,實(shí)際向線程池提交了五個(gè)任務(wù),但是當(dāng)i==0時(shí),產(chǎn)生了算術(shù)異常,線程池把該異常吃掉了,導(dǎo)致我們對(duì)該異常一無(wú)所知
解決辦法:
1.把submit改為execute
2.對(duì)線程池進(jìn)行擴(kuò)展,對(duì)submit進(jìn)行包裝
package com; import java.util.concurrent.*; public class Text09 { public static void main(String[] args) { //創(chuàng)建線程池 使用自定義的線程池 ExecutorService executorService=new TranceThreadPoorExcuter(5,5,0, TimeUnit.SECONDS,new SynchronousQueue<>()); //向線程池中添加兩個(gè)數(shù)相處計(jì)算的任務(wù) for (int i = 0; i <5 ; i++) { executorService.submit(new Text(10,i)); } } public static class Text implements Runnable { public int x; public int y; public Text(int x,int y) { this.x=x; this.y=y; } @Override public void run() { System.out.println(Thread.currentThread().getName()+"線程x/y結(jié)果的為"+x+"/"+y+"="+(x/y)); } } //自定義線程池類 對(duì)TranceThreadPoorExcuter進(jìn)行擴(kuò)展 private static class TranceThreadPoorExcuter extends ThreadPoolExecutor { public TranceThreadPoorExcuter(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue); } //定義一個(gè)方法用于傳入兩個(gè)參數(shù) 第一個(gè)是要接受的任務(wù) 第二個(gè)是Exception public Runnable warp(Runnable r,Exception e) { return new Runnable() { @Override public void run() { try { r.run(); } catch (Exception e1) { e.printStackTrace(); throw e1; } } }; } //重寫(xiě)submit方法 @Override public Future<?> submit(Runnable task) { return super.submit(warp(task,new Exception("客戶跟蹤異常"))); } //還可以重寫(xiě)excute方法 } }
上述就是小編為大家分享的怎么在Java中使用線程工廠監(jiān)控線程池了,如果剛好有類似的疑惑,不妨參照上述分析進(jìn)行理解。如果想知道更多相關(guān)知識(shí),歡迎關(guān)注億速云行業(yè)資訊頻道。
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