Java多线程六
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1 线程池的实现原理及基本类结构
合理利用线程池能够带来三个好处。
- 降低资源消耗。通过重复利用已创建的线程降低线程创建和销毁造成的消耗。
- 提高响应速度。当任务到达时，任务可以不需要等到线程创建就能立即执行。
- 提高线程的可管理性。线程是稀缺资源，如果无限制的创建，不仅会消耗系统资源，还会降低系统的稳定性，使用线程池可以进行统一的分配，调优和监控。
Executor线程池框架的最大优点是把任务的提交和执行解耦。客户端将要执行的任务封装成Task，然后提交即可。而Task如何执行客户端则是透明的。具体点讲，提交一个Callable对象给ExecutorService（如最常用的线程池ThreadPoolExecutor），将得到一个Future对象，调用Future对象的get方法等待执行结果。
下图是线程池所涉及到的所有类的结构图（右键查看大图），先从整体把握下： 
图1 线程池实现原理类结构图
上面这个图是很复杂的，涉及到了线程池内部实现原理的所有类，不利于我们理解线程池如何使用。我们先从客户端的角度出发，看看客户端使用线程池所涉及到的类结构图： 
图2 线程池使用的基本类结构图
从图一可知，实际的线程池类是实现ExecutorService接口的类，有ThreadPoolExecutor、ForkJoinPool和ScheduledThreadPoolExecutor。下面以常用的ThreadPoolExecutor为例讲解。
2 线程池实现步骤
2.1 线程池的创建
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">ThreadPoolExecutor</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> corePoolSize, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> maximumPoolSize, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler)</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
参数说明：
- corePoolSize（线程池的基本线程数）： the number of threads to keep in the pool, even if they are idle, unless
allowCoreThreadTimeOutis set.当提交一个任务到线程池时，线程池会创建一个线程来执行任务，即使其他空闲的基本线程能够执行新任务也会创建线程，等到需要执行的任务数大于线程池基本大小时就不再创建。如果调用了线程池的prestartAllCoreThreads方法，线程池会提前创建并启动所有基本线程。 - maximumPoolSize（线程池最大线程数）： the maximum number of threads to allow in the pool.线程池允许创建的最大线程数。如果任务队列满了，并且已创建的线程数小于最大线程数，则线程池会再创建新的线程执行任务。值得注意的是如果使用了无界的任务队列这个参数就没什么效果。
- keepAliveTime（线程活动保持时间）：when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.线程池的工作线程空闲后，保持存活的时间。所以如果任务很多，并且每个任务执行的时间比较短，可以调大这个时间，提高线程的利用率。
- TimeUnit（线程活动保持时间的单位）：the time unit for the keepAliveTime argument. 可选的单位有天（DAYS），小时（HOURS），分钟（MINUTES），毫秒(MILLISECONDS)，微秒(MICROSECONDS, 千分之一毫秒)和毫微秒(NANOSECONDS, 千分之一微秒)。
- workQueue（任务队列）：the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method.用于保存等待执行的任务的阻塞队列。 可以选择以下几个阻塞队列。
ArrayBlockingQueue：是一个基于数组结构的有界阻塞队列，此队列按 FIFO（先进先出）原则对元素进行排序。
LinkedBlockingQueue：一个基于链表结构的阻塞队列，此队列按FIFO （先进先出） 排序元素，吞吐量通常要高于ArrayBlockingQueue。静态工厂方法Executors.newFixedThreadPool()使用了这个队列。
SynchronousQueue：一个不存储元素的阻塞队列。每个插入操作必须等到另一个线程调用移除操作，否则插入操作一直处于阻塞状态，吞吐量通常要高于LinkedBlockingQueue，静态工厂方法Executors.newCachedThreadPool使用了这个队列。
PriorityBlockingQueue：一个具有优先级的无限阻塞队列。 - ThreadFactory：用于设置创建线程的工厂，可以通过线程工厂给每个创建出来的线程设置更有意义的名字。
- RejectedExecutionHandler（饱和策略）：当队列和线程池都满了，说明线程池处于饱和状态，那么必须采取一种策略处理提交的新任务。这个策略默认情况下是AbortPolicy，表示无法处理新任务时抛出异常。以下是JDK1.5提供的四种策略。
AbortPolicy：直接抛出异常。
CallerRunsPolicy：只用调用者所在线程来运行任务。
DiscardOldestPolicy：丢弃队列里最近的一个任务，并执行当前任务。
DiscardPolicy：不处理，丢弃掉。
当然也可以根据应用场景需要来实现RejectedExecutionHandler接口自定义策略。如记录日志或持久化不能处理的任务。
由此可见，创建一个线程所需的参数很多，线程池为我们提供了类Executors的静态工厂方法以创建不同类型的线程池。
- newFixedThreadPool可以生成固定大小的线程池;
- newCachedThreadPool可以生成一个无界、可以自动回收的线程池;
- newSingleThreadScheduledExecutor可以生成一个单个线程的线程池;
- newScheduledThreadPool还可以生成支持周期任务的线程池。
2.2 向线程池提交任务
有两种方式提交任务：
1.使用void execute(Runnable command)方法提交任务
execute方法返回类型为void，所以没有办法判断任务是否被线程池执行成功。
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Runnable task = new Runnable() { @Override public void run() { System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Task is running by "</span> + Thread<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.currentThread</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getName</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池正在执行的线程数："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getActiveCount</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> }}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>(task)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>2.使用submit方法提交任务 Future<?> submit(Runnable task);、<T> Future<T> submit(Runnable task, T result);和 Future<T> submit(Callable<T> task);会返回一个Future，可以通过这个future来判断任务是否执行成功，通过future的get方法来获取返回值，get方法会阻塞直到任务完成，而使用get(long timeout, TimeUnit unit)方法则会阻塞一段时间后立即返回，这时有可能任务没有执行完。
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Future<?> future = threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.submit</span>(task)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>try { Object result = future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.get</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"任务是否完成："</span> + future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isDone</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"返回的结果为："</span> + result)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>} catch (InterruptedException | ExecutionException e) { e<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printStackTrace</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>} finally { // 关闭线程池 threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.shutdown</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>2.3 线程池关闭
shutdown()方法：这个方法会平滑地关闭ExecutorService，当我们调用这个方法时，ExecutorService停止接受任何新的任务且等待已经提交的任务执行完成(已经提交的任务会分两类：一类是已经在执行的，另一类是还没有开始执行的)，当所有已经提交的任务执行完毕后将会关闭ExecutorService。awaitTermination(long timeout, TimeUnit unit)方法：这个方法有两个参数，一个是timeout即超时时间，另一个是unit即时间单位。这个方法会使当前关闭线程池的线程等待timeout时长，当超过timeout时间后，则去监测ExecutorService是否已经关闭，若关闭则返回true，否则返回false。一般情况下会和shutdown方法组合使用。shutdownNow()方法：这个方法会强制关闭ExecutorService，它将取消所有运行中的任务和在工作队列中等待的任务，这个方法返回一个List列表，列表中返回的是等待在工作队列中的任务。
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">// <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4.</span> 关闭线程池threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.shutdown</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>// hreadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.shutdownNow</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池是否关闭："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isShutdown</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>try { //当前线程阻塞<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>ms后，去检测线程池是否终止，终止则返回true while(!threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.awaitTermination</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MILLISECONDS</span>)) { System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"检测线程池是否终止："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isTerminated</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> }} catch (InterruptedException e) { e<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printStackTrace</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>}System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池是否终止："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isTerminated</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>完整案例：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">package <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">com</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.markliu</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.threadpool</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ExecutionException</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ExecutorService</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Executors</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Future</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ThreadPoolExecutor</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>import java<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.util</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.concurrent</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.TimeUnit</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>public class ThreadPoolDemo1 { public static void main(String[] args) { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* * 1. 创建线程池 * * 创建一个固定线程数目的线程池。corePoolSize = maximumPoolSize = 5 * 即线程池的基本线程数和最大线程数相等。 * 相当于： * new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>()); */</span> ExecutorService threadPool = Executors<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newFixedThreadPool</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* * 2. 封装任务并提交给线程池 */</span> ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) threadPool<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> Runnable task = new Runnable() { @Override public void run() { System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Task is running by "</span> + Thread<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.currentThread</span>()<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getName</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池正在执行的线程数："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getActiveCount</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> try { TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.SECONDS</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.sleep</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } catch (InterruptedException e) { e<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printStackTrace</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } } }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* * Starts all core threads, causing them to idly wait for work. * This overrides the default policy of starting core threads * only when new tasks are executed. */</span> int count = threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.prestartAllCoreThreads</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"开启的所有core线程数："</span> + count)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池当前线程数："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getPoolSize</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池的core number of threads："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getCorePoolSize</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池中的最大线程数："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getLargestPoolSize</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> // <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3.</span> 执行，获取返回结果 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * execute方式提交任务 */</span> // threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.execute</span>(task)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * submit方式提交任务 */</span> Future<?> future = threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.submit</span>(task)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> try { // 阻塞，等待线程执行完成，并获得结果 Object result = future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.get</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"任务是否完成："</span> + future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isDone</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"返回的结果为："</span> + result)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } catch (InterruptedException | ExecutionException e) { e<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printStackTrace</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } finally { System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池中已经执行完的任务数："</span> + threadPoolExecutor<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getCompletedTaskCount</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> // <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4.</span> 关闭线程池 <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* * shutdown方法平滑地关闭线程池，将线程池的状态设为：SHUTDOWN * 停止接受任何新的任务且等待已经提交的任务执行完成,当所有已经 * 提交的任务执行完毕后将会关闭线程池 */</span> threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.shutdown</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* * shutdownNow方法强制关闭线程池，将线程池状态设置为：STOP * 取消所有运行中的任务和在工作队列中等待的任务，并返回所有未执行的任务List */</span> // hreadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.shutdownNow</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池是否关闭："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isShutdown</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> try { //当前线程阻塞<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>ms后，去检测线程池是否终止，终止则返回true while(!threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.awaitTermination</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, TimeUnit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.MILLISECONDS</span>)) { System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"检测线程池是否终止："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isTerminated</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } } catch (InterruptedException e) { e<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.printStackTrace</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } System<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.out</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.println</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"线程池是否终止："</span> + threadPool<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isTerminated</span>())<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span> } }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li></ul>3 线程池的执行流程分析
线程池的主要工作流程如下图：
当提交一个新任务到线程池时，线程池的处理流程如下：
- 首先线程池判断“基本线程池”（corePoolSize）是否已满？没满，创建一个工作线程来执行任务。满了，则进入下个流程。
- 其次线程池判断工作队列（workQueue）是否已满？没满，则将新提交的任务存储在工作队列里。满了，则进入下个流程。
- 最后线程池判断整个线程池的线程数是否已超过maximumPoolSize？没满，则创建一个新的工作线程来执行任务，满了，则交给拒绝策略来处理这个任务。
（我的理解：提交任务—>如果线程数未达到corePoolSize，则创建线程执行任务—>如果达到corePoolSize，仍让提交了任务，则会有任务等待，所以将任务保存在任务队列中，直到任务队列workQueue已满—>如果workQueue已满，仍然有任务提交，但未达到最大线程数，则继续创建线程执行任务，直到线程数达到maximumPoolSize，如果达到了maximumPoolSize，则根据饱和策略拒绝该任务。这也就解释了为什么有了corePoolSize还有maximumPoolSize的原因。）
关于线程池的工作原理后期从源代码分析。
4 线程池的监控
通过线程池提供的参数进行监控：
- taskCount：线程池需要执行的任务数量。
- completedTaskCount：线程池在运行过程中已完成的任务数量。小于或等于taskCount。
- largestPoolSize：线程池曾经创建过的最大线程数量。通过这个数据可以知道线程池是否满过。如等于线程池的最大大小，则表示线程池曾经满了。
- getPoolSize:线程池的线程数量。如果线程池不销毁的话，池里的线程不会自动销毁，所以这个大小只增不减
- getActiveCount：获取活动的线程数。
通过继承线程池并重写线程池的beforeExecute，afterExecute和terminated方法，可以在任务执行前，执行后和线程池关闭前干一些事情。如监控任务的平均执行时间，最大执行时间和最小执行时间等。这几个方法在线程池里是空方法。
<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 给定的Thread执行Runnable之前调用此方法 * *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> t the thread that will run task {@code r} *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> r the task that will be executed */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">beforeExecute</span>(Thread t, Runnable r) { } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 给定的Runnable完成后执行此方法 * This method is invoked by the thread that executed the task. *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> r the runnable that has completed *<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @param</span> t the exception that caused termination, or null if * execution completed normally */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">afterExecute</span>(Runnable r, Throwable t) { } <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/** * 当Executor终止时调用此方法. * 注意：方法中子类应调用super.terminated() */</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">terminated</span>() { }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>例如：
<code class="hljs php has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ExtendedExecutor</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ThreadPoolExecutor</span> {</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ...</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">protected</span> void afterExecute(Runnable r, Throwable t) { super.afterExecute(r, t); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (t == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> && r <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">instanceof</span> Future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;"><?</span>>) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { Object result = ((Future<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;"><?</span>>) r).get(); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (CancellationException ce) { t = ce; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (ExecutionException ee) { t = ee.getCause(); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException ie) { Thread.currentThread().interrupt(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// ignore/reset</span> } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (t != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) System.out.println(t); }}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li></li></ul> 0 0
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