简单了解JDK1.8的5种线程池

ゝ一纸荒年。 2023-02-15 10:27 2阅读 0赞

<table> 
 <thead> 
  <tr> 
   <th>线程池</th> 
   <th colspan="5">构造函数</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>&nbsp;</td> 
   <td>核心线程</td> 
   <td>最大线程</td> 
   <td>线程存活时间</td> 
   <td colspan="2">队列</td> 
  </tr> 
  <tr> 
   <td>FixThreadPool</td> 
   <td>?</td> 
   <td>等于核心线程数</td> 
   <td>永久</td> 
   <td colspan="2">LinkBlockingQuque</td> 
  </tr> 
  <tr> 
   <td>SingleThreadPool</td> 
   <td>1</td> 
   <td>1</td> 
   <td>永久</td> 
   <td colspan="2">LinkBlockingQuque</td> 
  </tr> 
  <tr> 
   <td>CacheThreadPool</td> 
   <td>?</td> 
   <td>Integer.MAX_VALUE</td> 
   <td>60秒</td> 
   <td colspan="2">SynchronousQueue</td> 
  </tr> 
  <tr> 
   <td>ScheduledThreadPool</td> 
   <td>?</td> 
   <td>Integer.MAX_VALUE</td> 
   <td>永久</td> 
   <td colspan="2">DelayedWorkQueue</td> 
  </tr> 
  <tr> 
   <td>WorkStealingPool</td> 
   <td>可用CPU核心数</td> 
   <td>&nbsp;</td> 
   <td>&nbsp;</td> 
   <td colspan="2"> <p>内部类WorkQueue</p> <p>&nbsp;</p> </td> 
  </tr> 
 </tbody> 
</table>

我们在初始化线程池时经常用以下写法(**不优雅**)：

ExecutorService executorService = Executors.newFixedThreadPool(8);

如果该线程池使用场景，task无限多，会造成一个什么问题？

很显然LinkBlockingQueue队列长度我们没有赋值，他会默认Integer.MAX\_VALUE，可能会由于队列中待执行任务过多而发生Out\_of\_Memory

CacheThreadPool与ScheduledThreadPool由于最大线程数为Integer.MAX\_VALUE，亦有可能Out\_Of\_Memory

**建议写法**：

//创建固定长度线程池、单线程池
    ExecutorService executorService = new ThreadPoolExecutor(1,1,0L,
                    TimeUnit.MICROSECONDS,new LinkedBlockingQueue<>(2));
    
    //创建可变长度线程池
     ExecutorService executorService = new ThreadPoolExecutor(0,2,30L,
                    TimeUnit.DAYS,new SynchronousQueue<Runnable>(true)); 
    
    //创建延迟(定时)线程池
    ExecutorService executorService = new ThreadPoolExecutor(1,5,0L,
                    TimeUnit.MICROSECONDS,new DelayedWorkQueue<>(5));
    
    
    //创建workStealing线程池，我更喜欢叫他任务份发线程池
     ForkJoinPool forkJoinPool =  new ForkJoinPool(7,
                    ForkJoinPool.defaultForkJoinWorkerThreadFactory,null, true);