单线程线程池 newSingleThreadExecutor

╰+攻爆jí腚メ 2024-03-22 19:36 60阅读 0赞

### newSingleThreadExecutor ###

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

<table> 
 <thead> 
  <tr> 
   <th align="left">SingleThreadExecutor是使用单个worker线程的Executor</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">SingleThreadExecutor的corePoolSize和maximumPoolSize被设置为<code>1</code>。其他参数与FixedThreadPool相同。</td> 
  </tr> 
  <tr> 
   <td align="left">SingleThreadExecutor使用无界队列<code>LinkedBlockingQueue</code>作为线程池的工作队列（队列的容量为Integer.MAX_VALUE）。SingleThreadExecutor使用无界队列作为工作队列对线程池带来的影响与FixedThreadPool相同，这里就不赘述了。</td> 
  </tr> 
 </tbody> 
</table>

![在这里插入图片描述][9f871f5bd89243c2b807399bd296978b.png_pic_center]

<table> 
 <thead> 
  <tr> 
   <th align="left"></th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">1）如果当前运行的线程数少于corePoolSize（即线程池中无运行的线程），则创建一个新线程来执行任务。</td> 
  </tr> 
  <tr> 
   <td align="left">2）在线程池完成预热之后（当前线程池中有一个运行的线程），将任务加入<code>LinkedBlockingQueue</code>。</td> 
  </tr> 
  <tr> 
   <td align="left">3）线程执行完<code>1</code>中的任务后，会在一个无限循环中反复从LinkedBlockingQueue获取任务来执行。</td> 
  </tr> 
 </tbody> 
</table>

### 常见用途 ###

参考：[Executor框架的成员][Executor]

--------------------

### 线程任务 ###

public class Task implements Runnable {
        
        private final String name;
    
        public Task(String name) {
        
            this.name = name;
        }
    
        @Override
        public void run() {
        
            System.out.println(Thread.currentThread().getName() + " → " + name + " Start Time = " + new Date());
            processCommand();
            System.out.println(Thread.currentThread().getName() + " → " + name + " End   Time = " + new Date());
        }
    
        private void processCommand() {
        
            try {
        
                Thread.sleep(3000);
            } catch (InterruptedException e) {
        
                e.printStackTrace();
            }
        }
    }

### 单线程线程池 newSingleThreadExecutor ###

public class SingleThreadPool {
        
        public static void main(String args[]) throws InterruptedException, ExecutionException {
        
            System.out.println(Thread.currentThread().getName() + "线程: Start at: " + new Date());
    
            ExecutorService exec = Executors.newSingleThreadExecutor(); // 创建大小为1的固定线程池
            // 等价于 ExecutorService exec = Executors.newFixedThreadPool(1);
    
            for (int i = 1; i < 10; i++) {
        
                System.out.println("添加了第" + i + "个任务类");
                exec.execute(new Task(String.valueOf(i)));
            }
    
            exec.shutdown();
    
            System.out.println(Thread.currentThread().getName() + "线程: Finished all threads at：" + new Date() + ". isTerminated 判断次数 ");
        }
    }

### 执行结果分析 ###

<table> 
 <thead> 
  <tr> 
   <th align="left">执行结果</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">main线程: Start at: Fri May 19 21:48:50 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第1个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第2个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第3个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第4个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第5个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第6个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第7个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第8个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">添加了第9个任务类</td> 
  </tr> 
  <tr> 
   <td align="left">main线程: Finished all threads at：Fri May 19 21:48:50 CST 2023. isTerminated 判断次数</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 1 Start Time = Fri May 19 21:48:50 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 1 End Time = Fri May 19 21:48:53 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 2 Start Time = Fri May 19 21:48:53 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 2 End Time = Fri May 19 21:48:56 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 3 Start Time = Fri May 19 21:48:56 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 3 End Time = Fri May 19 21:48:59 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 4 Start Time = Fri May 19 21:48:59 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 4 End Time = Fri May 19 21:49:02 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 5 Start Time = Fri May 19 21:49:02 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 5 End Time = Fri May 19 21:49:05 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 6 Start Time = Fri May 19 21:49:05 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 6 End Time = Fri May 19 21:49:08 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 7 Start Time = Fri May 19 21:49:08 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 7 End Time = Fri May 19 21:49:11 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 8 Start Time = Fri May 19 21:49:11 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 8 End Time = Fri May 19 21:49:14 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 9 Start Time = Fri May 19 21:49:14 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left">pool-1-thread-1 → 9 End Time = Fri May 19 21:49:17 CST 2023</td> 
  </tr> 
  <tr> 
   <td align="left"></td> 
  </tr> 
  <tr> 
   <td align="left"><strong>从控制台结果可以看出：</strong></td> 
  </tr> 
  <tr> 
   <td align="left">线程池创建<code>1</code>个线程来 执行这<code>9</code>个任务。单例线程，任意时间池中只能有<code>1</code>个线程</td> 
  </tr> 
  <tr> 
   <td align="left">主线程的执行与线程池里的线程分开，有可能主线程结束了，但是线程池还在运行</td> 
  </tr> 
  <tr> 
   <td align="left">它能保证线程的<code>先后顺序执行</code>，并且能保证一条线程执行完成后才开启另一条新的线程</td> 
  </tr> 
 </tbody> 
</table>

[9f871f5bd89243c2b807399bd296978b.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/55e35e4110574d5bb3215a25d1fbfe5f.png
[Executor]: https://blog.csdn.net/weixin_37646636/article/details/131028935