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
*/
public class MyThread extends Thread {
/**
* MyThreadPool object, from which the task to be run
*/
private MyThreadPool pool;
private boolean active = true;
public boolean isActive() {
return active;
}
public void setPool(MyThreadPool 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 result = pool.getResultListener();
Callable 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 block
e.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 {
private Object waitLock = new Object();
public Object getWaitLock() {
return waitLock;
}
/**
* list of threads for completing submitted tasks
*/
private final LinkedList> threads;
/**
* submitted task will be kept in this list untill they run by one of
* threads in pool
*/
private final LinkedList> tasks;
/**
* shutDown flag to shut Down service
*/
private volatile boolean shutDown;
/**
* ResultListener to get back the result of submitted tasks
*/
private ResultListener 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 myResultListener) {
tasks = new LinkedList>();
threads = new LinkedList>();
shutDown = false;
resultListener = myResultListener;
for (int i = 0; i < size; i++) {
MyThread myThread = new MyThread();
myThread.setPool(this);
threads.add(myThread);
myThread.start();
}
}
public ResultListener getResultListener() {
return resultListener;
}
public void setResultListener(ResultListener resultListener) {
this.resultListener = resultListener;
}
public boolean isShutDown() {
return shutDown;
}
public int getThreadPoolSize() {
return threads.size();
}
public synchronized Callable removeFromQueue() {
return tasks.poll();
}
public synchronized void addToTasks(Callable 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 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 mythread : threads) {
mythread.shutdown();
}
synchronized (this.waitLock) {
waitLock.notifyAll();
}
for (MyThread mythread : threads) {
try {
mythread.join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.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{
@Override
public void finish(Object obj) {
}
@Override
public 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 MatchedCountResultListener
implements 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
*/
@Override
public void finish(V obj) {
//System.out.println('count is '+obj);
matchedCount.addAndGet((Integer)obj);
}
/**
* print exception thrown in running the task
*/
@Override
public 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 {
CompletionService
threadService;
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();
MyThreadPool
newPool = 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;
}
@Override
public 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