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Executors的newSingleThreadExecutor()和newFixedThreadPool(1)有什么區(qū)別？

Java

料青山看我應(yīng)如是 2019-03-01 10:31:38

Executors的newSingleThreadExecutor()和newFixedThreadPool(1)有什么區(qū)別？參考了一些文章，都說newSingleThreadExecutor()主要有兩個特性：能保證執(zhí)行順序，先提交的先執(zhí)行。當(dāng)線程執(zhí)行中出現(xiàn)異常，去創(chuàng)建一個新的線程替換之。講到和newFixedThreadPool(1)的區(qū)別，都主要指出如下。 http://www.cnblogs.com/richaa...文章中：和 newFixedThreadPool(1) 的區(qū)別在于，如果線程遇到錯誤中止，它是無法使用替代線程的。 http://blog.csdn.net/vking_wa...文章中：如果當(dāng)前線程意外終止，會創(chuàng)建一個新線程繼續(xù)執(zhí)行任務(wù)，這和我們直接創(chuàng)建線程不同，也和newFixedThreadPool(1)不同。但經(jīng)過我的實驗（代碼如下），得出兩者都是一樣的，都保證了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); } ); 運行結(jié)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 創(chuàng)建newSingleThreadExecutor的源碼中，其實是在newFixedThreadPool(1)的基礎(chǔ)上包裝了FinalizableDelegatedExecutorService，請問下這個究竟有啥用？麻煩幫忙解答。 public static ExecutorService newSingleThreadExecutor() { return new FinalizableDelegatedExecutorService (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())); }

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GCT1015

TA貢獻(xiàn)1827條經(jīng)驗獲得超4個贊

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

這是jdk8源碼上面的注釋，大體上的意思是 newSingleThreadExecutor 不能配置去重新加入線程；
接下來舉個栗子

    // 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
為什么呢？

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

看上面的代碼 FinalizableDelegatedExecutorService extends DelegatedExecutorService，而DelegatedExecutorService的主要作用就是不暴露那么多方法，不讓你配置線程池，至此，single就真的single了

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反對回復(fù) 2019-03-01