主要定義一個線程池應該具備的基本操作和方法
public interface ThreadPool {
/**
* 提交任務到線程池
*
* @param runnable
*/
void execute(Runnable runnable);
/**
* 關閉線程池
*/
void shutdown();
/**
* 初始化大小
*/
int getInitSize();
/**
* 獲取線程池最大線程數
*
* @return
*/
int getMaxsize();
/**
* 獲取線程池最大的線程數
*
* @return
*/
int getCoreSize();
/**
* 獲取線程池中用於緩存任務隊列的大小
*
* @return
*/
int getQuenSize();
/**
* 獲取線程池中活躍線程的數量
*
* @return
*/
int getActiveCount();
/**
* 查詢線程池是否已經關閉
*
* @return
*/
boolean isShutdown();
}
主要存放用於提交的Runnable,並且有limit限制
public interface RunnableQueue {
/**
* 當有新的任務進來時，放到隊列的末尾
*
* @param offer
*/
void offer(Runnable offer);
/**
* 工作線程通過task獲取任務
*
* @return
*/
Runnable task();
/**
* 獲取線程池緩存任務的數量
*
* @return
*/
int size();
}
當RunnableQueue超出範圍時，使用拒絕策略
@FunctionalInterface
public interface DenyPolicy {
void reject(Runnable runnable, ThreadPool threadPool);
/**
* 直接丟棄任務
*/
class DiscardDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
//TODO
}
}
/**
* 該拒絕策略會向任務提交者拋出異常
*/
class AbortDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
throw new RunnableDenyPolicyException("");
}
}
//該拒絕策略會使任務在提交者所在的線程執行
class RunnerDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
if (!threadPool.isShutdown()) {
runnable.run();
}
}
}
}
public class RunnableDenyPolicyException extends RuntimeException {
public RunnableDenyPolicyException(String message) {
super(message);
}
}
主要用於線程池內部，不斷從queue中取出某個runnable,並運行run方法
public class InternalTask implements Runnable {
/**
* 任務隊列
*/
private final RunnableQueue runnableQueue;
/**
* 標記
*/
private volatile boolean running = true;
public InternalTask(RunnableQueue runnableQueue) {
this.runnableQueue = runnableQueue;
}
@Override
public void run() {
//當前任務爲running並且沒有被中斷，則不從隊列獲取下一個任務，
while (running && !Thread.currentThread().isInterrupted()) {
try {
//獲取任務
Runnable task = runnableQueue.task();
task.run();
} catch (Exception e) {
running = false;
break;
}
}
}
//停止當前任務
public void stop() {
this.running = false;
}
}
public class LinkendRunnableQueue implements RunnableQueue {
/**
* 隊列最大長度
*/
private final int limit;
/**
* 拒絕策略
*/
private final DenyPolicy denyPolicy;
/**
* 存放任務
*/
private final LinkedList<Runnable> runnableList = new LinkedList<>();
/**
* 線程池
*/
private final ThreadPool threadPool;
public LinkendRunnableQueue(int limit, DenyPolicy denyPolicy, ThreadPool threadPool) {
this.limit = limit;
this.denyPolicy = denyPolicy;
this.threadPool = threadPool;
}
@Override
public void offer(Runnable runnable) {
synchronized (runnableList) {
if (runnableList.size() >= limit) {
//超過限制，啓動拒絕策略
this.denyPolicy.reject(runnable, threadPool);
} else {
//將入到隊列
runnableList.addLast(runnable);
runnableList.notifyAll();
}
}
}
@Override
public Runnable task() {
synchronized (runnableList) {
while (runnableList.isEmpty()) {
try {
//如果沒有任務進來，阻塞
runnableList.wait();
} catch (Exception e) {
e.printStackTrace();
}
}
//從任務頭移除一個任務
return runnableList.removeFirst();
}
}
@Override
public int size() {
//返回線程池數量
synchronized (runnableList) {
return runnableList.size();
}
}
}
@FunctionalInterface
public interface ThreadFactory {
/**
* 用於創建線程
*
* @param runnable
* @return
*/
Thread createThread(Runnable runnable);
}
初始化線程池，需要有數量控制、創建線程工廠、隊列策略等
import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class BasicThreadPool extends Thread implements ThreadPool {
/**
* 初始化線程數量
*/
private final int initSize;
/**
* 線程池最大線程數量
*/
private final int maxSize;
/**
* 線程池核心線程數量
*/
private final int coreSize;
/**
* 當前活躍的線程數量
*/
private int activeCount;
/**
* 線程工廠
*/
private final ThreadFactory threadFactory;
/**
* 任務隊列
*/
private final RunnableQueue runnableQueue;
/**
* 是否停止線程池
*/
private volatile boolean isShutdown = false;
/**
* 時間
*/
private final long keepAliveTime;
/**
* 睡眠工具類
*/
private final TimeUnit timeUnit;
/**
* 任務隊列
*/
private final Queue<ThreadTask> threadQueue = new ArrayDeque();
private final static DenyPolicy DEFAULT_DENY_POLICY = new DenyPolicy.DiscardDenyPolicy();
private final static ThreadFactory DEFAULT_THREAD_FACTORY = new DefaultThreadFactory();
public BasicThreadPool(int initSize, int maxSize, int coreSize, int queueSize) {
this(initSize, maxSize, coreSize, DEFAULT_THREAD_FACTORY, queueSize, DEFAULT_DENY_POLICY, 10, TimeUnit.SECONDS);
}
public BasicThreadPool(int initSize, int maxSize, int coreSize, ThreadFactory defaultThreadFactory,
int queueSize, DenyPolicy defaultDenyPolicy, int keepAliveTime, TimeUnit timeUnit) {
this.initSize = initSize;
this.maxSize = maxSize;
this.coreSize = coreSize;
this.threadFactory = defaultThreadFactory;
this.runnableQueue = new LinkendRunnableQueue(queueSize, defaultDenyPolicy, this);
this.keepAliveTime = keepAliveTime;
this.timeUnit = timeUnit;
this.init();
}
/**
* 初始化
*/
private void init() {
start();
for (int i = 0; i < initSize; i++) {
newThread();
}
}
/**
* 擴容
*/
private void newThread() {
InternalTask internalTask = new InternalTask(runnableQueue);
Thread thread = this.threadFactory.createThread(internalTask);
ThreadTask threadTask = new ThreadTask(thread, internalTask);
threadQueue.offer(threadTask);
this.activeCount++;
thread.start();
}
private void removeThread() {
//從線程中移除某個線程
ThreadTask threadTask = threadQueue.remove();
threadTask.internalTask.stop();
this.activeCount--;
}
@Override
public void run() {
//用於維護線程數量，比如擴容、回收等工作
while (!isShutdown && !isInterrupted()) {
try {
timeUnit.sleep(keepAliveTime);
} catch (InterruptedException e) {
isShutdown = true;
break;
}
synchronized (this) {
if (isShutdown)
break;
if (runnableQueue.size() > 0 && activeCount < coreSize) {
for (int i = initSize; i < coreSize; i++) {
newThread();
}
continue;
}
if (runnableQueue.size() > 0 && activeCount < coreSize) {
for (int i = initSize; i < maxSize; i++) {
newThread();
}
}
if (runnableQueue.size() == 0 && activeCount > coreSize) {
for (int i = coreSize; i < activeCount; i++) {
removeThread();
}
}
}
}
}
@Override
public void execute(Runnable runnable) {
if (this.isShutdown)
throw new IllegalStateException("The thread pool is destroy");
//提交到隊列
this.runnableQueue.offer(runnable);
}
@Override
public void shutdown() {
synchronized (this) {
if (isShutdown) {
return;
}
isShutdown = true;
threadQueue.forEach(threadTask -> {
threadTask.internalTask.stop();
threadTask.thread.interrupt();
});
this.interrupt();
}
}
@Override
public int getInitSize() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.initSize;
}
@Override
public int getMaxsize() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.maxSize;
}
@Override
public int getCoreSize() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.coreSize;
}
@Override
public int getQuenSize() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.runnableQueue.size();
}
@Override
public int getActiveCount() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.activeCount;
}
@Override
public boolean isShutdown() {
if (isShutdown)
throw new IllegalStateException("The thread pool is destroy");
return this.isShutdown;
}
/**
* ThreadTask只是InternalTask和Thread結合
*/
private static class ThreadTask {
Thread thread;
InternalTask internalTask;
public ThreadTask(Thread thread, InternalTask internalTask) {
this.thread = thread;
this.internalTask = internalTask;
}
}
/**
* 默認線程池
*/
private static class DefaultThreadFactory implements ThreadFactory {
private static final AtomicInteger GROUP_COUNTER = new AtomicInteger(1);
private static final ThreadGroup group = new ThreadGroup("MyThreadPool-" + GROUP_COUNTER.getAndDecrement());
private static final AtomicInteger COUNTER = new AtomicInteger(0);
@Override
public Thread createThread(Runnable runnable) {
return new Thread(group, runnable, "thread-pool-" + COUNTER.getAndDecrement());
}
}
}
測試類
public class ThreadPoolTest {
public static void main(String[] args) throws InterruptedException {
final ThreadPool threadPool = new BasicThreadPool(10, 100, 10, 1000);
for (int i = 0; i < 20; i++) {
threadPool.execute(() -> {
try {
TimeUnit.SECONDS.sleep(10);
System.out.println(Thread.currentThread().getName() + " is running and done.");
} catch (InterruptedException e) {
e.printStackTrace();
}
});
for (; ; ) {
System.out.println("getActiveCount:" + threadPool.getActiveCount());
System.out.println("getCoreSize:" + threadPool.getCoreSize());
System.out.println("getMaxSize:" + threadPool.getMaxsize());
System.out.println("getRunnableQueue:" + threadPool.getQuenSize());
System.out.println("=================================");
TimeUnit.SECONDS.sleep(5);
}
}
}
}
這裏只是思路，還存在很多缺點不在優化。
1.BasicThreadPool和Thread不應該是繼承關係，採用組合最好。
2.線程池銷燬對未返回未完成的任務，導致任務丟失。
3.BasicThreadPool構造太多，建議建造者模式
4.線程池對數量控制並沒有校驗，initSize不應該大於MaxSize
5.其他自行考慮