package concurrent.threadpool;
/**
* @className: ThreadPool
* @description: 线程池接口
* @date: 2022/4/2
* @author: cakin
*/
public interface ThreadPool {
// 提交任务到线程池
void execute(Runnable runnable);
// 关闭线程池
void shutdown();
// 获取线程池的初始化大小
int getInitSize();
// 获取线程池的最大线程数
int getMaxSize();
// 获取线程池的核心线程数量
int getCoreSize();
// 获取线程池中用于获取任务队列的大小
int getQueueSize();
// 获取线程池中活跃线程数量
int getActiveCount();
// 查看线程池是否已经被 shutdown
boolean isShutdown();
}
package concurrent.threadpool;
/**
* @className: RunnableQueue
* @description: 任务队列,主要用于缓存提交到线程池中的任务
* @date: 2022/4/2
* @author: cakin
*/
public interface RunnableQueue {
// 当有新任务来时首先会 offer 到队列中
void offer(Runnable runnable);
// 工作线程通过 take 方法获取 Runnable
Runnable take() throws InterruptedException; //throws InterruptedException;
// 获取任务队列中任务的数量
int size();
}
package concurrent.threadpool;
/**
* @className: ThreadFactory
* @description: 线程工厂,提供创建线程的接口,以便于个性化地定制 Thread,比如 Thread 应该被放到哪个 Group 中,优先级、线程名字以及是否为守护线程等
* @date: 2022/4/2
* @author: cakin
*/
@FunctionalInterface
public interface ThreadFactory {
// 用于创建线程
Thread createThread(Runnable runnable);
}
package concurrent.threadpool;
/**
* @className: DenyPolicy
* @description: 拒绝策略:主要用于当 Queue 中的 Runnable 达到 limit 上限时,决定采用哪种策略通知提交者。该接口定义了三种默认实现
* @date: 2022/4/2
* @author: cakin
*/
@FunctionalInterface
public interface DenyPolicy {
void reject(Runnable runnable, ThreadPool threadPool);
// 该拒绝策略会直接将任务丢弃
class DiscardDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
// do nothing
}
}
// 该拒绝策略会向任务提交者抛出异常
class AbortDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
throw new RuntimeDenyException("The runnable " + runnable + " will be abort.");
}
}
// 该拒绝策略会使任务在提交者所在的线程中执行任务
class RunnerDenyPolicy implements DenyPolicy {
@Override
public void reject(Runnable runnable, ThreadPool threadPool) {
if (!threadPool.isShutdown()) {
runnable.run();
}
}
}
}
package concurrent.threadpool;
/**
* @className: RuntimeDenyException
* @description: 异常类:通知任务提交者,任务队列已无法再接受新的任务
* @date: 2022/4/2
* @author: cakin
*/
public class RuntimeDenyException extends RuntimeException {
public RuntimeDenyException(String message) {
super(message);
}
}
package concurrent.threadpool;
public class InternalTask implements Runnable {
private final RunnableQueue runnableQueue;
private volatile boolean running = true;
public InternalTask(RunnableQueue runnableQueue) {
this.runnableQueue = runnableQueue;
}
@Override
public void run() {
// 如果当前任务为 running 并且没有被中断,则其将不断从 queue 中获取 Runnable,然后执行 run 方法
while (running && !Thread.currentThread().isInterrupted()) {
try {
Runnable task = runnableQueue.take();
task.run();
} catch (Exception e) {
running = false;
break;
}
}
}
// 停止当前任务,主要会在线程池的 shutdown 方法中使用
public void stop() {
this.running = false;
}
}
package concurrent.threadpool;
import java.util.LinkedList;
public class LinkedRunnableQueue implements RunnableQueue {
// 任务队列的最大容量,在构造时传入
private final int limit;
// 若任务队列中的任务已满,则需要执行拒绝策略
private final DenyPolicy denyPolicy;
// 存放任务的队列
private final LinkedList<Runnable> runnableList = new LinkedList<>();
// 线程池
private final ThreadPool threadPool;
// 构造器
public LinkedRunnableQueue(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) {
// 无法容纳新的任务时执行拒绝策略
denyPolicy.reject(runnable, threadPool);
} else {
// 将任务加入到队尾,并且唤醒阻塞中的线程
runnableList.addLast(runnable);
runnableList.notifyAll();
}
}
}
@Override
public Runnable take() throws InterruptedException {
synchronized (runnableList) {
while (runnableList.isEmpty()) {
try {
// 如果任务队列中没有任务可执行任务,则当前线程会挂起,进入 runnableList 关联的 monitor waitset 中等待唤醒(新的任务加入)
runnableList.wait();
} catch (InterruptedException e) {
throw e;
}
}
// 从任务队列头部移除一个任务
return runnableList.removeFirst();
}
}
@Override
public int size() {
synchronized (runnableList) {
// 返回当前任务队列中的任务数
return runnableList.size();
}
}
}
package concurrent.threadpool;
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 {
// 初始化线程数量
private final int initSize;
// 线程池最大线程数量
private final int maxSize;
// 线程池核心线程数量
private final int coreSize;
// 当前活跃线程数量
private int activeCount;
// 创建线程所需工厂
private final ThreadFactory threadFactory;
// 任务队列
private final RunnableQueue runnableQueue;
// 线程池是否已经被 shutdown
private volatile boolean isShutdown = false;
// 工作线程队列,存放活动线程
private final Queue<ThreadTask> threadQueue = new ArrayDeque<>();
// 拒绝策略
private final static DenyPolicy DEFAULT_DENY_POLICY = new DenyPolicy.DiscardDenyPolicy();
// 线程工厂
private final static ThreadFactory DEFAULT_THREAD_FACTORY = new DefaultThreadFactory();
private final long keepAliveTime;
private final TimeUnit timeUnit;
// 构造队列时需要传递的参数:初始的线程数量,最大的线程数量,核心线程数量,任务队列的最大数量
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 threadFactory, int queueSize, DenyPolicy denyPolicy, int keepAliveTime, TimeUnit timeUnit) {
this.initSize = initSize;
this.maxSize = maxSize;
this.coreSize = coreSize;
this.threadFactory = threadFactory;
this.runnableQueue = new LinkedRunnableQueue(queueSize, denyPolicy, this);
this.keepAliveTime = keepAliveTime;
this.timeUnit = timeUnit;
this.init();
}
// 初始化时,先创建 initSize 个线程
private void init() {
// 启动 BasicThreadPool 自身线程
start();
for (int i = 0; i < initSize; i++) {
newThread();
}
}
private void newThread() {
// 创建任务线程,并且启动
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() {
// 从线程池中移除某个线程
ThreadTask threadTask = threadQueue.remove();
threadTask.internalTask.stop();
this.activeCount--;
}
// 将 runnable 插入 runnableQueue 中即可
@Override
public void execute(Runnable runnable) {
if (isShutdown) {
throw new IllegalStateException("the thread pool is destroy");
}
// 提交任务只是简单地将任务队列中插入 runnable
this.runnableQueue.offer(runnable);
}
// 为了停止 BasicThreadPool 线程,停止线程池中的活动线程并且将 isShutdown 开关变量更改为 true
@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 getQueueSize() {
if (isShutdown) {
throw new IllegalStateException("the thread pool is destroy");
}
return runnableQueue.size();
}
@Override
public int getActiveCount() {
synchronized (this){
return this.activeCount;
}
}
@Override
public boolean isShutdown() {
return this.isShutdown;
}
// 主要用于维护线程数量,比如扩容、回收等工作
@Override
public void run() {
while (!isShutdown && !isInterrupted()) {
try {
timeUnit.sleep(keepAliveTime);
} catch (InterruptedException e) {
isShutdown = true;
break;
}
synchronized (this) {
if (isShutdown) {
break;
}
// 当前队列中有任务尚未处理,并且 activeCount < coreSize 则继续扩容
if (runnableQueue.size() > 0 && activeCount < coreSize) {
for (int i = initSize; i < coreSize; i++) {
newThread();
}
// countinue 的目前在于不想让线程的扩容直接打到 maxSize
continue;
}
// 当前队列中有任务尚未处理,并且 activeCount < maxSize 则继续扩容
if (runnableQueue.size() > 0 && activeCount < maxSize) {
for (int i = coreSize; i < maxSize; i++) {
newThread();
}
}
// 如果任务队列中没有任务,则需要回收,回收到 coreSize
if (runnableQueue.size() == 0 && activeCount > coreSize) {
for (int i = coreSize; i < activeCount; i++) {
removeThread();
}
}
}
}
}
// ThreadTask 只是 InterTask 和 Thread 的一个组合
private static class ThreadTask {
public ThreadTask(Thread thread, InternalTask internalTask) {
this.thread = thread;
this.internalTask = internalTask;
}
Thread thread;
InternalTask internalTask;
}
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());
}
}
}
package concurrent.threadpool;
import java.util.concurrent.TimeUnit;
public class ThreadPoolTest {
public static void main(String[] args) {
// 定义线程池,初始化线程为2,核心线程为4,最大线程为6,任务队列允许1000个任务
final ThreadPool threadPool = new BasicThreadPool(2, 6, 4, 1000);
// 定义 20 个任务并且提交线程池
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 (; ; ) {
// 不断输出线程池的信息
System.out.println("getActiveCount:" + threadPool.getActiveCount());
System.out.println("getQueueSize:" + threadPool.getQueueSize());
System.out.println("getCoreSize:" + threadPool.getCoreSize());
System.out.println("getMaxSize:" + threadPool.getMaxSize());
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
getActiveCount:2
getQueueSize:18
getCoreSize:4
getMaxSize:6
getActiveCount:2
getQueueSize:18
getCoreSize:4
getMaxSize:6
thread-pool--1 is running and done.
thread-pool-0 is running and done.
getActiveCount:4
getQueueSize:14
getCoreSize:4
getMaxSize:6
getActiveCount:4
getQueueSize:14
getCoreSize:4
getMaxSize:6
thread-pool--3 is running and done.
thread-pool--2 is running and done.
thread-pool--1 is running and done.
thread-pool-0 is running and done.
getActiveCount:6
getQueueSize:8
getCoreSize:4
getMaxSize:6
getActiveCount:6
getQueueSize:8
getCoreSize:4
getMaxSize:6
thread-pool--3 is running and done.
thread-pool--4 is running and done.
thread-pool--2 is running and done.
thread-pool--5 is running and done.
thread-pool-0 is running and done.
thread-pool--1 is running and done.
getActiveCount:6
getQueueSize:2
getCoreSize:4
getMaxSize:6
getActiveCount:6
getQueueSize:2
getCoreSize:4
getMaxSize:6
thread-pool--4 is running and done.
thread-pool--3 is running and done.
thread-pool--2 is running and done.
thread-pool--5 is running and done.
thread-pool--1 is running and done.
thread-pool-0 is running and done.
getActiveCount:6
getQueueSize:0
getCoreSize:4
getMaxSize:6
getActiveCount:6
getQueueSize:0
getCoreSize:4
getMaxSize:6
thread-pool--4 is running and done.
thread-pool--3 is running and done.
getActiveCount:5
getQueueSize:0
getCoreSize:4
getMaxSize:6
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