Executors的newSingleThreadExecutor()和newFixedThreadPool(1)有什么区别？

Question

Executors的newSingleThreadExecutor()和newFixedThreadPool(1)有什么区别？ 参考了一些文章，都说newSingleThreadExecutor()主要有两个特性： 能保证执行顺序，先提交的先执行。 当线程执行中出现异常，去创建一个新的线程替换之。 讲到和newFixedThreadPool(1)的区别，都主要指出如下。 http://www.cnblogs.com/richaa...文章中： 和 newFixedThreadPool(1) 的区别在于，如果线程遇到错误中止，它是无法使用替代线程的。 http://blog.csdn.net/vking_wa...文章中： 如果当前线程意外终止，会创建一个新线程继续执行任务，这和我们直接创建线程不同，也和newFixedThreadPool(1)不同。 但经过我的实验（代码如下），得出两者都是一样的，都保证了1和2。 // ExecutorService executorService = Executors.newSingleThreadExecutor(); ExecutorService executorService = Executors.newFixedThreadPool(1); executorService.execute( () -> { if (count == 100) { thrownewIllegalStateException("handler exception"); } System.out.println(Thread.currentThread()+" - testAsyncRunner1 run ... "+count); } ); 运行结果： Thread[pool-1-thread-1,5,main] - testAsyncRunner1 run ... 99 Exception in thread "pool-1-thread-1" java.lang.IllegalStateException: handler exception at com.mxx.meal.common.core.async.AsyncHandlerFactoryTest.lambda$null$0(AsyncHandlerFactoryTest.java:32) at com.mxx.meal.common.core.async.AsyncHandlerFactoryTest$$Lambda$2/830539025.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Thread[pool-1-thread-2,5,main] - testAsyncRunner1 run ... 101 创建newSingleThreadExecutor的源码中，其实是在newFixedThreadPool(1)的基础上包装了FinalizableDelegatedExecutorService，请问下这个究竟有啥用？麻烦帮忙解答。 public static ExecutorService newSingleThreadExecutor() { return new FinalizableDelegatedExecutorService (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())); }

Answer 1

     //  Unlike the otherwise equivalent
     // {@code newFixedThreadPool(1)} the returned executor is
     // guaranteed not to be reconfigurable to use additional threads.
      public static ExecutorService newSingleThreadExecutor() 

这是jdk8源码上面的注释，大体上的意思是 newSingleThreadExecutor 不能配置去重新加入线程；
接下来 举个栗子

    // final ExecutorService single = Executors.newSingleThreadExecutor();
       final ExecutorService fixed = Executors.newFixedThreadPool(1);
        ThreadPoolExecutor executor = (ThreadPoolExecutor) fixed;
        executor.setCorePoolSize(4);

就是上面的意思
为什么呢？

 /**
     * A wrapper class that exposes only the ExecutorService methods
     * of an ExecutorService implementation.
     */
    static class DelegatedExecutorService extends AbstractExecutorService 

看上面的代码 FinalizableDelegatedExecutorService extends DelegatedExecutorService，而DelegatedExecutorService的主要作用就是不暴露那么多方法，不让你配置线程池，至此，single就真的single了

以上

Answer 2

lalala, i'm the express of nature