本文主要是介绍通过使用策略模式模拟实现Java线程池逻辑和研究线程池的实现原理，自己一定要动手写一下才知道里面的奥妙。，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前几天写了一个固定大小的连接池，今天通过学习又整理一下线程池的实现逻辑，看完这片代码，Java线程池的基本思想你就能完全hold住，离着高级程序员又近一步，欢迎大家参考和交流。
package com.smallfan.connectionpool;import lombok.extern.slf4j.Slf4j;import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashSet;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;/*** @PACKAGE_NAME: com.smallfan.connectionpool* @NAME: TestThreadPool* @USER: dell* @DATE: 2020/5/29* @PROJECT_NAME: aboutthread*/
@Slf4j
public class TestThreadPool {public static void main(String[] args) {ThreadPool threadPool = new ThreadPool(1, 1000,TimeUnit.MILLISECONDS, 1, ((queue, task) -> {//死等
// queue.takeQueue();//设置超时
// Object o = queue.takeQueueForTime(500, TimeUnit.MILLISECONDS);//舍弃
// log.info("不干预，放弃 {}",task);//抛出异常
// throw new RuntimeException("抛出异常"+task);//交给主线程执行task.run();}));for (int i = 0; i < 5; i++) {int j = i;threadPool.execute(() ->{try {Thread.sleep(1000L);} catch (InterruptedException e) {e.printStackTrace();}log.info("执行第" + j);});}}
}@Slf4j
class ThreadPool {//任务对列private BlockingQueue<Runnable> taskQueue;//线程集合private HashSet workers = new HashSet<Worker>();//线程数private int threadSize;//超时时间private long timeout;//时间单位private TimeUnit timeUnit;//拒绝策略private RejectPolicy<Runnable> policy;public ThreadPool(int threadSize, long timeout, TimeUnit timeUnit, int capacity, RejectPolicy<Runnable> policy) {this.threadSize = threadSize;this.timeout = timeout;this.timeUnit = timeUnit;taskQueue = new BlockingQueue<>(capacity);this.policy = policy;}public void execute(Runnable task) {synchronized (workers) {//公共资源保证线程安全//如果任务数小于threadSize时直接执行//否则加入到线程对列if (workers.size() < threadSize) {log.info("新增worker{}", task);Worker worker = new Worker(task);workers.add(worker);worker.start();} else {//taskQueue.putQueue(task);/*** 考虑问题* 1对列满了死等* 2设置超时时间* 3舍弃* 4主线程执行* 5抛出异常* 使用设计模式的策略模式解决*/taskQueue.tryPut(policy, task);}}}@FunctionalInterfaceinterface RejectPolicy<T> {void reject(BlockingQueue<T> queue, T task);}class Worker extends Thread {private Runnable runnable;public Worker(Runnable runnable) {this.runnable = runnable;}@Overridepublic void run() {/*** 执行任务* 1.当runnable直接执行* 2.当对列里面存在任务时执行*/
// while (runnable != null || (runnable = taskQueue.takeQueue()) != null) {while (runnable != null || (runnable = taskQueue.takeQueueForTime(timeout, timeUnit)) != null) {try {log.info("执行worker{}", runnable);runnable.run();} catch (Exception e) {e.printStackTrace();} finally {runnable = null;//执行后置空}}synchronized (workers) {log.info("移除worker{}", this);workers.remove(this);}}}
}//模拟阻塞队列
@Slf4j
class BlockingQueue<T> {//1.定义队列大小private int capacity;//2.定义双向链表，当做容器private Deque<T> deque = new ArrayDeque<T>();//3.定义锁private ReentrantLock lock = new ReentrantLock();//4.定义空条件变量private Condition emptyWaitSet = lock.newCondition();//5.定义满条件变量private Condition fullWaitSet = lock.newCondition();public BlockingQueue(int capacity) {this.capacity = capacity;}//定义获取方法public T takeQueue() {lock.lock();try {while (deque.isEmpty()) {//若还没有try {emptyWaitSet.await();//空等待放入时唤醒} catch (InterruptedException e) {e.printStackTrace();}}//若已经放入T t = deque.removeFirst();fullWaitSet.signal();//唤醒满条件return t;} finally {lock.unlock();//释放锁，避免死锁}}//定义超时获取public T takeQueueForTime(long timeout, TimeUnit unit) {lock.lock();long nanos = unit.toNanos(timeout);//统一时间单位try {while (deque.isEmpty()) {//若还没有try {if (nanos <= 0) {return null;}nanos = emptyWaitSet.awaitNanos(nanos);//防止虚假唤醒 使用等待时间减去消耗时间} catch (InterruptedException e) {e.printStackTrace();}}//若已经放入T t = deque.removeFirst();fullWaitSet.signal();//唤醒满条件return t;} finally {lock.unlock();//释放锁，避免死锁}}//定义放入方法public void putQueue(T task) {lock.lock();try {while (deque.size() == capacity) {//已经满了try {fullWaitSet.await();} catch (InterruptedException e) {e.printStackTrace();}}deque.addLast(task);emptyWaitSet.signal();log.info("加入队列 {}", task);} finally {lock.unlock();}}/*** 任务多时，设置添加任务的超时时间** @param task* @param timeout* @param timeUnit* @return*/public boolean putQueueForTimeOut(T task, long timeout, TimeUnit timeUnit) {lock.lock();long nanos = timeUnit.toNanos(timeout);try {while (deque.size() == capacity) {//已经满了try {if (nanos <= 0) {//添加失败return false;}nanos = fullWaitSet.awaitNanos(nanos);} catch (InterruptedException e) {e.printStackTrace();}}deque.addLast(task);emptyWaitSet.signal();return true;//添加成功} finally {lock.unlock();}}//获取容量public int getCapacity() {lock.lock();try {return deque.size();} finally {lock.unlock();}}public void tryPut(ThreadPool.RejectPolicy<T> policy, T task) {lock.lock();try {if (deque.size() == capacity) {//对列已满 调用策略 让调用者决定policy.reject(this, task);} else {//空闲deque.addLast(task);emptyWaitSet.signal();}} finally {lock.unlock();}}
}
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