自定义java线程池

ThreadPoolExecutor是Java并发api添加的一项功能，可以有效地维护和重用线程，因此我们的程序不必担心创建和销毁线程，也不必关注核心功能。 我创建了一个自定义线程池执行程序，以更好地了解线程池执行程序的工作方式。

功能性：

• 它维护一个固定的线程池，即使没有任务提交也创建线程并启动线程，而ThreadPoolExecutor根据需要创建线程，即，每当将可运行对象提交给池且线程数小于核心池大小时。
• 在ThreadPoolExecutor中，我们提供了一个等待队列，当所有线程忙于运行现有任务时，新的可运行任务将在该队列中等待。 队列填满后，将创建最大线程池大小的新线程。 在MyThreadPool中，我将可运行对象存储在链接列表中，因此每个任务都将在列表中等待并且不受限制，因此在此不使用maxPoolSize。
• 在ThreadPoolExecutor中，我们使用Future Objects从任务中获取结果，如果结果不可用，则future.get（）方法将阻塞，或者使用CompletionService。 在MyThreadPoolExecutor中，我创建了一个名为ResultListener的简单接口，用户必须提供对此的实现，如他希望如何处理输出。 每个任务完成后，ResultListener将获得带有任务输出的回调，或者在发生任何异常的情况下将调用error方法。
• 调用shutdown方法时，MyThreadPoolExecutor将停止接受新任务并完成剩余任务。
• 与ThreadPoolExecutor相比，我提供了非常基本的功能，我使用了简单的线程机制，如wait（），notify（），notifyAll（）和join（）。
• 在性能方面，它类似于ThreadPoolExecutor，在某些情况下好一些。 如果您发现任何有趣的结果或改进方法，请告诉我。

package com.util;import java.util.concurrent.Callable;/*** Run submitted task of {@link MyThreadPool} After running the task , It calls* on {@link ResultListener}object with {@link Output}which contains returned* result of {@link Callable}task. Waits if the pool is empty.* * @author abhishek* * @param */import java.util.concurrent.Callable;
/**
* Run submitted task of {@link MyThreadPool} After running the task , It calls
* on {@link ResultListener}object with {@link Output}which contains returned
* result of {@link Callable}task. Waits if the pool is empty.
*
* @author abhishek
*
* @param <V>
*/
public class MyThread<V> extends Thread {/*** MyThreadPool object, from which the task to be run*/private MyThreadPool<V> pool;private boolean active = true;public boolean isActive() {return active;}public void setPool(MyThreadPool<V> p) {pool = p;}/*** Checks if there are any unfinished tasks left. if there are , then runs* the task and call back with output on resultListner Waits if there are no* tasks available to run If shutDown is called on MyThreadPool, all waiting* threads will exit and all running threads will exit after finishing the* task*/public void run() {ResultListener<V> result = pool.getResultListener();Callable<V> task;while (true){task = pool.removeFromQueue();if (task != null){try{V output = task.call();result.finish(output);} catch (Exception e){result.error(e);}} else{if (!isActive())break;else{synchronized (pool.getWaitLock()){try{pool.getWaitLock().wait();} catch (InterruptedException e){// TODO Auto-generated catch blocke.printStackTrace();}}}}}}void shutdown() {active = false;}
}

package com.util;
import java.util.LinkedList;
import java.util.concurrent.Callable;
/**
* This class is used to execute submitted {@link Callable} tasks. this class
* creates and manages fixed number of threads User will provide a
* {@link ResultListener}object in order to get the Result of submitted task
*
* @author abhishek
*
*
*/
public class MyThreadPool<V> {private Object waitLock = new Object();public Object getWaitLock() {return waitLock;}/*** list of threads for completing submitted tasks*/private final LinkedList<MyThread<V>> threads;/*** submitted task will be kept in this list untill they run by one of* threads in pool*/private final LinkedList<Callable<V>> tasks;/*** shutDown flag to shut Down service*/private volatile boolean shutDown;/*** ResultListener to get back the result of submitted tasks*/private ResultListener<V> resultListener;/*** initializes the threadPool by starting the threads threads will wait till* tasks are not submitted** @param size* Number of threads to be created and maintained in pool* @param myResultListener* ResultListener to get back result*/public MyThreadPool(int size, ResultListener<V> myResultListener) {tasks = new LinkedList<Callable<V>>();threads = new LinkedList<MyThread<V>>();shutDown = false;resultListener = myResultListener;for (int i = 0; i < size; i++) {MyThread<V> myThread = new MyThread<V>();myThread.setPool(this);threads.add(myThread);myThread.start();}}public ResultListener<V> getResultListener() {return resultListener;}public void setResultListener(ResultListener<V> resultListener) {this.resultListener = resultListener;}public boolean isShutDown() {return shutDown;}public int getThreadPoolSize() {return threads.size();}public synchronized Callable<V> removeFromQueue() {return tasks.poll();}public synchronized void addToTasks(Callable<V> callable) {tasks.add(callable);}/*** submits the task to threadPool. will not accept any new task if shutDown* is called Adds the task to the list and notify any waiting threads** @param callable*/public void submit(Callable<V> callable) {if (!shutDown) {addToTasks(callable);synchronized (this.waitLock) {waitLock.notify();}} else {System.out.println('task is rejected.. Pool shutDown executed');}}/*** Initiates a shutdown in which previously submitted tasks are executed,* but no new tasks will be accepted. Waits if there are unfinished tasks* remaining**/public void stop() {for (MyThread<V> mythread : threads) {mythread.shutdown();}synchronized (this.waitLock) {waitLock.notifyAll();}for (MyThread<V> mythread : threads) {try {mythread.join();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}
}

package com.util;/*** This interface imposes finish method * which is used to get the {@link Output} object * of finished task* @author abhishek** @param */public interface ResultListener {public void finish(T obj);public void error(Exception ex);}

您可以根据需要实现此类并返回并处理任务返回的结果。

package com.util;public class DefaultResultListener implements ResultListener{@Overridepublic void finish(Object obj) {}@Overridepublic void error(Exception ex) {ex.printStackTrace();}}

例如，此类将添加task返回的数字。

package com.util;import java.util.concurrent.atomic.AtomicInteger;/*** ResultListener class to keep track of total matched count* @author abhishek* * @param */
public class MatchedCountResultListenerimplements ResultListener{/*** matchedCount to keep track of the number of matches returned by submitted* task*/AtomicInteger matchedCount = new AtomicInteger();/*** this method is called by ThreadPool to give back the result of callable* task. if the task completed successfully then increment the matchedCount by* result count*/@Overridepublic void finish(V obj) {//System.out.println('count is '+obj);matchedCount.addAndGet((Integer)obj);}/*** print exception thrown in running the task*/@Overridepublic void error(Exception ex) {ex.printStackTrace();}/*** returns the final matched count of all the finished tasks* * @return*/public int getFinalCount() {return matchedCount.get();}
}

这是一个测试类，使用CompletionService和MyThreadPoolExecutor对循环运行简单

package test;import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;import com.util.DefaultResultListener;
import com.util.MyThreadPool;public class TestClass {public static void main(String[] args) throws InterruptedException {CompletionServicethreadService;ExecutorService service = Executors.newFixedThreadPool(2);threadService = new ExecutorCompletionService(service);long b = System.currentTimeMillis();for(int i =0;i<50000;i++){threadService.submit(new MyRunable (i));}service.shutdown();System.out.println('time taken by Completion Service ' + (System.currentTimeMillis()-b));DefaultResultListener result = new DefaultResultListener();MyThreadPoolnewPool = new MyThreadPool(2,result);long a = System.currentTimeMillis();int cc =0;for(int i =0;i<50000;i++){cc = cc+i;}System.out.println('time taken without any pool ' + (System.currentTimeMillis()-a));a= System.currentTimeMillis();for(int i =0;i<5000;i++){newPool.submit(new MyRunable (i));}newPool.stop();System.out.println('time taken by myThreadPool ' + (System.currentTimeMillis()-a));}}class MyRunable implements Callable{int index = -1;public MyRunable(int index){this.index = index;}@Overridepublic Integer call() throws Exception {return index;}}

参考： 我的JCG合作伙伴 Abhishek Somani在Java，J2EE和Server博客上的Java 自定义线程池执行程序 。

翻译自: https://www.javacodegeeks.com/2013/03/my-custom-thread-pool-executor-in-java.html

自定义java线程池