一、自定义线程池

1. 简易线程池

@Slf4j(topic = "c.TestPool")
public class TestPool {public static void main(String[] args) {ThreadPool threadPool = new ThreadPool(2,1000, TimeUnit.MILLISECONDS, 10);for (int i = 0; i < 5; i++) {int j =i;threadPool.execute(() -> {log.debug("{}",j);});}}}@Slf4j(topic = "c.ThreadPool")
class ThreadPool {// 任务队列private BlockingQueue taskQueue;// 线程集合private HashSet workers = new HashSet<>();// 核心线程数private int coreSize;// 获取任务时的超时时间private long timeout;private TimeUnit timeUnit;public ThreadPool(int coreSize, long timeout, TimeUnit timeUnit, int queueCapcity) {this.coreSize = coreSize;this.timeout = timeout;this.timeUnit = timeUnit;this.taskQueue = new BlockingQueue<>(queueCapcity);}// 执行任务public void execute(Runnable task) {// 当任务数没有超过 coreSize 时，直接交给 worker 对象执行// 如果任务数超过 coreSize 时，加入任务队列暂存synchronized (workers) {if (workers.size() < coreSize) {Worker worker = new Worker(task);log.debug("新增 worker{}, {}", worker, task);workers.add(worker);worker.start();} else {taskQueue.put(task);}}}class Worker extends Thread {private Runnable task;public Worker(Runnable task) {this.task = task;}@Overridepublic void run() {// 执行任务// 1) 当 task 不为空，执行任务// 2) 当 task 执行完毕，再接着从任务队列获取任务并执行
//            while (task != null || (task = taskQueue.take()) != null) {while(task != null || (task = taskQueue.poll(timeout, timeUnit)) != null) {try {log.debug("正在执行...{}", task);task.run();} catch (Exception e) {e.printStackTrace();} finally {task = null;}}synchronized (workers) {log.debug("worker 被移除{}", this);workers.remove(this);}}}
}// 阻塞队列
@Slf4j(topic = "c.BlockingQueue")
class BlockingQueue {// 1. 任务队列private Deque queue = new ArrayDeque<>();// 2. 锁private ReentrantLock lock = new ReentrantLock();// 3. 生产者条件变量private Condition fullWaitSet = lock.newCondition();// 4. 消费者条件变量private Condition emptyWaitSet = lock.newCondition();// 5. 容量private int capcity;public BlockingQueue(int capcity) {this.capcity = capcity;}// 带超时阻塞获取public T poll(long timeout, TimeUnit unit) {lock.lock();try {// 将 timeout 统一转换为 纳秒long nanos = unit.toNanos(timeout);while (queue.isEmpty()) {try {if (nanos <= 0) {return null;}// 返回值是剩余时间nanos = emptyWaitSet.awaitNanos(nanos);} catch (InterruptedException e) {e.printStackTrace();}}T t = queue.removeFirst();fullWaitSet.signal();return t;} finally {lock.unlock();}}// 阻塞获取public T take() {lock.lock();try {while (queue.isEmpty()) {try {emptyWaitSet.await();} catch (InterruptedException e) {e.printStackTrace();}}T t = queue.removeFirst();fullWaitSet.signal();return t;} finally {lock.unlock();}}// 阻塞添加public void put(T task) {lock.lock();try {while (queue.size() == capcity) {try {log.debug("等待加入任务队列 {} ...", task);fullWaitSet.await();} catch (InterruptedException e) {e.printStackTrace();}}log.debug("加入任务队列 {}", task);queue.addLast(task);emptyWaitSet.signal();} finally {lock.unlock();}}public int size() {lock.lock();try {return queue.size();} finally {lock.unlock();}}
}

2. 拒绝策略

@Slf4j(topic = "c.TestPool")
public class TestPool {public static void main(String[] args) {ThreadPool threadPool = new ThreadPool(1,1000, TimeUnit.MILLISECONDS, 1, (queue, task)->{// 1. 死等
//            queue.put(task);// 2) 带超时等待
//            queue.offer(task, 1500, TimeUnit.MILLISECONDS);// 3) 让调用者放弃任务执行
//            log.debug("放弃{}", task);// 4) 让调用者抛出异常
//            throw new RuntimeException("任务执行失败 " + task);// 5) 让调用者自己执行任务task.run();});for (int i = 0; i < 4; i++) {int j = i;threadPool.execute(() -> {try {Thread.sleep(1000L);} catch (InterruptedException e) {e.printStackTrace();}log.debug("{}", j);});}}
}@FunctionalInterface // 拒绝策略
interface RejectPolicy {void reject(BlockingQueue queue, T task);
}@Slf4j(topic = "c.ThreadPool")
class ThreadPool {// 任务队列private BlockingQueue taskQueue;// 线程集合private HashSet workers = new HashSet<>();// 核心线程数private int coreSize;// 获取任务时的超时时间private long timeout;private TimeUnit timeUnit;private RejectPolicy rejectPolicy;// 执行任务public void execute(Runnable task) {// 当任务数没有超过 coreSize 时，直接交给 worker 对象执行// 如果任务数超过 coreSize 时，加入任务队列暂存synchronized (workers) {if(workers.size() < coreSize) {Worker worker = new Worker(task);log.debug("新增 worker{}, {}", worker, task);workers.add(worker);worker.start();} else {
//                taskQueue.put(task);// 1) 死等// 2) 带超时等待// 3) 让调用者放弃任务执行// 4) 让调用者抛出异常// 5) 让调用者自己执行任务taskQueue.tryPut(rejectPolicy, task);}}}public ThreadPool(int coreSize, long timeout, TimeUnit timeUnit, int queueCapcity, RejectPolicy rejectPolicy) {this.coreSize = coreSize;this.timeout = timeout;this.timeUnit = timeUnit;this.taskQueue = new BlockingQueue<>(queueCapcity);this.rejectPolicy = rejectPolicy;}class Worker extends Thread{private Runnable task;public Worker(Runnable task) {this.task = task;}@Overridepublic void run() {// 执行任务// 1) 当 task 不为空，执行任务// 2) 当 task 执行完毕，再接着从任务队列获取任务并执行
//            while(task != null || (task = taskQueue.take()) != null) {while(task != null || (task = taskQueue.poll(timeout, timeUnit)) != null) {try {log.debug("正在执行...{}", task);task.run();} catch (Exception e) {e.printStackTrace();} finally {task = null;}}synchronized (workers) {log.debug("worker 被移除{}", this);workers.remove(this);}}}
}
@Slf4j(topic = "c.BlockingQueue")
class BlockingQueue {// 1. 任务队列private Deque queue = new ArrayDeque<>();// 2. 锁private ReentrantLock lock = new ReentrantLock();// 3. 生产者条件变量private Condition fullWaitSet = lock.newCondition();// 4. 消费者条件变量private Condition emptyWaitSet = lock.newCondition();// 5. 容量private int capcity;public BlockingQueue(int capcity) {this.capcity = capcity;}// 带超时阻塞获取public T poll(long timeout, TimeUnit unit) {lock.lock();try {// 将 timeout 统一转换为 纳秒long nanos = unit.toNanos(timeout);while (queue.isEmpty()) {try {// 返回值是剩余时间if (nanos <= 0) {return null;}nanos = emptyWaitSet.awaitNanos(nanos);} catch (InterruptedException e) {e.printStackTrace();}}T t = queue.removeFirst();fullWaitSet.signal();return t;} finally {lock.unlock();}}// 阻塞获取public T take() {lock.lock();try {while (queue.isEmpty()) {try {emptyWaitSet.await();} catch (InterruptedException e) {e.printStackTrace();}}T t = queue.removeFirst();fullWaitSet.signal();return t;} finally {lock.unlock();}}// 阻塞添加public void put(T task) {lock.lock();try {while (queue.size() == capcity) {try {log.debug("等待加入任务队列 {} ...", task);fullWaitSet.await();} catch (InterruptedException e) {e.printStackTrace();}}log.debug("加入任务队列 {}", task);queue.addLast(task);emptyWaitSet.signal();} finally {lock.unlock();}}// 带超时时间阻塞添加public boolean offer(T task, long timeout, TimeUnit timeUnit) {lock.lock();try {long nanos = timeUnit.toNanos(timeout);while (queue.size() == capcity) {try {if(nanos <= 0) {return false;}log.debug("等待加入任务队列 {} ...", task);nanos = fullWaitSet.awaitNanos(nanos);} catch (InterruptedException e) {e.printStackTrace();}}log.debug("加入任务队列 {}", task);queue.addLast(task);emptyWaitSet.signal();return true;} finally {lock.unlock();}}public int size() {lock.lock();try {return queue.size();} finally {lock.unlock();}}public void tryPut(RejectPolicy rejectPolicy, T task) {lock.lock();try {// 判断队列是否满if(queue.size() == capcity) {rejectPolicy.reject(this, task);} else {  // 有空闲log.debug("加入任务队列 {}", task);queue.addLast(task);emptyWaitSet.signal();}} finally {lock.unlock();}}
}

二、ThreadPoolExecutor

 1. 线程池状态

ThreadPoolExecutor 使用 int 的高 3 位来表示线程池状态，低 29 位表示线程数量

从数字上比较，TERMINATED > TIDYING > STOP > SHUTDOWN > RUNNING 

这些信息存储在一个原子变量 ctl 中，目的是将线程池状态与线程个数合二为一，这样就可以用一次 cas 原子操作进行赋值

2. 构造方法（***）

public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler)

（1）corePoolSize 核心线程数目 (最多保留的线程数) （2）maximumPoolSize 最大线程数目 （3）keepAliveTime 生存时间 - 针对救急线程 （4）unit 时间单位 - 针对救急线程 （5）workQueue 阻塞队列 （6）threadFactory 线程工厂 - 可以为线程创建时起个好名字 （7）handler 拒绝策略

工作方式：  

 （1）线程池中刚开始没有线程，当一个任务提交给线程池后，线程池会创建一个新线程来执行任务。

（2）当线程数达到 corePoolSize 并没有线程空闲，这时再加入任务，新加的任务会被加入workQueue 队列排队，直到有空闲的线程。 （3）如果队列选择了有界队列，那么任务超过了队列大小时，会创建 maximumPoolSize - corePoolSize 数目的线程来救急。 （4）如果线程到达 maximumPoolSize 仍然有新任务这时会执行拒绝策略。拒绝策略 jdk 提供了 4 种实现，其它著名框架也提供了实现 1️⃣AbortPolicy 让调用者抛出 RejectedExecutionException 异常，这是默认策略 2️⃣CallerRunsPolicy 让调用者运行任务 3️⃣DiscardPolicy 放弃本次任务 4️⃣DiscardOldestPolicy 放弃队列中最早的任务，本任务取而代之 5️⃣Dubbo 的实现，在抛出 RejectedExecutionException 异常之前会记录日志，并 dump 线程栈信息，方便定位问题 6️⃣Netty 的实现，是创建一个新线程来执行任务 7️⃣ActiveMQ 的实现，带超时等待（60s）尝试放入队列，类似我们之前自定义的拒绝策略 8️⃣PinPoint 的实现，它使用了一个拒绝策略链，会逐一尝试策略链中每种拒绝策略 （5）当高峰过去后，超过corePoolSize 的救急线程如果一段时间没有任务做，需要结束节省资源，这个时间由 keepAliveTime 和 unit 来控制。

拒绝策略 

根据这个构造方法，JDK Executors 类中提供了众多工厂方法来创建各种用途的线程池

3. newFixedThreadPool（固定大小线程池）

public static ExecutorService newFixedThreadPool(int nThreads) {return new ThreadPoolExecutor(nThreads, nThreads,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue());}

特点： （1）核心线程数 == 最大线程数（没有救急线程被创建），因此也无需超时时间 （2）阻塞队列是无界的，可以放任意数量的任务

评价 适用于任务量已知，相对耗时的任务

public class TestThreadPoolExecutors {public static void main(String[] args) {ExecutorService pool = Executors.newFixedThreadPool(2);ExecutorService pool2 = Executors.newFixedThreadPool(2, new ThreadFactory() {private AtomicInteger t = new AtomicInteger(1);@Overridepublic Thread newThread(Runnable r) {return new Thread(r, "mypool_t" + t.getAndIncrement());}});pool.execute(() -> {log.debug("1");});pool.execute(() -> {log.debug("1");});pool.execute(() -> {log.debug("1");});}
}

4. newCachedThreadPool（带缓冲功能线程池）

public static ExecutorService newCachedThreadPool() {return new ThreadPoolExecutor(0, Integer.MAX_VALUE,60L, TimeUnit.SECONDS,new SynchronousQueue());}

特点： （1）核心线程数是 0， 最大线程数是 Integer.MAX_VALUE，救急线程的空闲生存时间是 60s，意味着 1️⃣全部都是救急线程（60s 后可以回收） 2️⃣救急线程可以无限创建 （2）队列采用了 SynchronousQueue 实现特点是，它没有容量，没有线程来取是放不进去的（一手交钱、一手交货）

@Slf4j(topic = "c.TestSynchronousQueue")
public class TestSynchronousQueue {public static void main(String[] args) {SynchronousQueue integers = new SynchronousQueue<>();new Thread(() -> {try {log.debug("putting {} ", 1);integers.put(1);log.debug("{} putted...", 1);log.debug("putting...{} ", 2);integers.put(2);log.debug("{} putted...", 2);} catch (InterruptedException e) {e.printStackTrace();}},"t1").start();sleep(1);new Thread(() -> {try {log.debug("taking {}", 1);integers.take();} catch (InterruptedException e) {e.printStackTrace();}},"t2").start();sleep(1);new Thread(() -> {try {log.debug("taking {}", 2);integers.take();} catch (InterruptedException e) {e.printStackTrace();}},"t3").start();}
}

评价

（1）整个线程池表现为线程数会根据任务量不断增长，没有上限，当任务执行完毕，空闲 1分钟后释放线程。 （2）适合任务数比较密集，但每个任务执行时间较短的情况

5. newSingleThreadExecutor（单线程线程池）

public static ExecutorService newSingleThreadExecutor() {return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue()));}

使用场景： 希望多个任务排队执行。线程数固定为 1，任务数多于 1 时，会放入无界队列排队。任务执行完毕，这唯一的线程也不会被释放。

区别： （1）自己创建一个单线程串行执行任务，如果任务执行失败而终止那么没有任何补救措施，而线程池还会新建一个线程，保证池的正常工作 （2）Executors.newSingleThreadExecutor() 线程个数始终为1，不能修改 1️⃣FinalizableDelegatedExecutorService 应用的是装饰器模式，只对外暴露了 ExecutorService 接口，因此不能调用 ThreadPoolExecutor 中特有的方法 （3）Executors.newFixedThreadPool(1) 初始时为1，以后还可以修改 1️⃣对外暴露的是 ThreadPoolExecutor 对象，可以强转后调用 setCorePoolSize 等方法进行修改

@Slf4j(topic = "c.TestExecutors")
public class TestExecutors {public static void main(String[] args) throws InterruptedException {test2();}public static void test2() {ExecutorService pool = Executors.newSingleThreadExecutor();pool.execute(() -> {log.debug("1");int i = 1 / 0;log.debug("111");});pool.execute(() -> {log.debug("2");});pool.execute(() -> {log.debug("3");});}}

6. 提交任务

    // 执行任务void execute(Runnable command);// 提交任务 task，用返回值 Future 获得任务执行结果 Future submit(Callable task);// 提交 tasks 中所有任务 List> invokeAll(Collection> tasks)throws InterruptedException;// 提交 tasks 中所有任务，带超时时间 List> invokeAll(Collection> tasks,long timeout, TimeUnit unit)throws InterruptedException;// 提交 tasks 中所有任务，哪个任务先成功执行完毕，返回此任务执行结果，其它任务取消 T invokeAny(Collection> tasks)throws InterruptedException, ExecutionException;// 提交 tasks 中所有任务，哪个任务先成功执行完毕，返回此任务执行结果，其它任务取消，带超时时间 T invokeAny(Collection> tasks,long timeout, TimeUnit unit)throws InterruptedException, ExecutionException, TimeoutException;}

@Slf4j(topic = "c.TestSubmit")
public class TestSubmit {public static void main(String[] args) throws ExecutionException, InterruptedException {ExecutorService pool = Executors.newFixedThreadPool(1);}private static void method3(ExecutorService pool) throws InterruptedException, ExecutionException {String result = pool.invokeAny(Arrays.asList(() -> {log.debug("begin 1");Thread.sleep(1000);log.debug("end 1");return "1";},() -> {log.debug("begin 2");Thread.sleep(500);log.debug("end 2");return "2";},() -> {log.debug("begin 3");Thread.sleep(2000);log.debug("end 3");return "3";}));log.debug("{}", result);}private static void method2(ExecutorService pool) throws InterruptedException {List> futures = pool.invokeAll(Arrays.asList(() -> {log.debug("begin");Thread.sleep(1000);return "1";},() -> {log.debug("begin");Thread.sleep(500);return "2";},() -> {log.debug("begin");Thread.sleep(2000);return "3";}));futures.forEach( f ->  {try {log.debug("{}", f.get());} catch (InterruptedException | ExecutionException e) {e.printStackTrace();}});}private static void method1(ExecutorService pool) throws InterruptedException, ExecutionException {// new Callable<>()Future future = pool.submit(() -> {log.debug("running");Thread.sleep(1000);return "ok";});log.debug("{}", future.get());}
}

7. 关闭线程池

7.1 shutdown

/*
线程池状态变为 SHUTDOWN- 不会接收新任务- 但已提交任务会执行完- 此方法不会阻塞调用线程的执行
*/
void shutdown();

    public void shutdown() {final ReentrantLock mainLock = this.mainLock;mainLock.lock();try {checkShutdownAccess();// 修改线程池状态advanceRunState(SHUTDOWN);// 仅会打断空闲线程interruptIdleWorkers();onShutdown(); // 扩展点 ScheduledThreadPoolExecutor} finally {mainLock.unlock();}// 尝试终结(没有运行的线程可以立刻终结，如果还有运行的线程也不会等)tryTerminate();}

7.2 shutdownNow 

/*
线程池状态变为 STOP- 不会接收新任务- 会将队列中的任务返回- 并用 interrupt 的方式中断正在执行的任务
*/
List shutdownNow();

    public List shutdownNow() {List tasks;final ReentrantLock mainLock = this.mainLock;mainLock.lock();try {checkShutdownAccess();// 修改线程池状态advanceRunState(STOP);// 打断所有线程interruptWorkers();// 获取队列中剩余任务tasks = drainQueue();} finally {mainLock.unlock();}// 尝试终结tryTerminate();return tasks;}

7.3 其他方法 

    // 不在 RUNNING 状态的线程池，此方法就返回 trueboolean isShutdown();// 线程池状态是否是 TERMINATEDboolean isTerminated();// 调用 shutdown 后，由于调用线程并不会等待所有任务运行结束，因此如果它想在线程池 TERMINATED 后做些事情，可以利用此方法等待boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException;

7.4 演示

@Slf4j(topic = "c.TestShutDown")
public class TestShutDown {public static void main(String[] args) throws ExecutionException, InterruptedException {ExecutorService pool = Executors.newFixedThreadPool(2);Future result1 = pool.submit(() -> {log.debug("task 1 running...");Thread.sleep(1000);log.debug("task 1 finish...");return 1;});Future result2 = pool.submit(() -> {log.debug("task 2 running...");Thread.sleep(1000);log.debug("task 2 finish...");return 2;});Future result3 = pool.submit(() -> {log.debug("task 3 running...");Thread.sleep(1000);log.debug("task 3 finish...");return 3;});log.debug("shutdown");
//        pool.shutdown();
//        pool.awaitTermination(3, TimeUnit.SECONDS);List runnables = pool.shutdownNow();log.debug("other.... {}" , runnables);}
}