Java：newFixedThreadPool大小為5，出現pool-2-thread-6怎么回事？

參考官方文檔

public static ExecutorService newFixedThreadPool(int nThreads)

創(chuàng)建一個線程池, 在重用共享無界隊列中運行的固定線程數。在任何時候, nThreads 個線程都將是活動的處理任務。如果在所有線程都處于活動狀態(tài)時提交了其他任務, 則它們將在隊列中等待, 直到線程可用為止。如果由于在關閉前執(zhí)行過程中出現故障而終止了任何線程, 則如果需要執(zhí)行后續(xù)任務, 則新項將取代它。池中的線程將存在, 直到顯式關閉為止。

可以用下面的程序測試

import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;

public class ThreadPoolTest1 {
    
    static class MyTask implements Runnable {
        private String name;
        
        public MyTask(String name){
            this.name = name;
        }

        
        @Override
        public void run() {
            for (int i = 0; i < 2; i++) {
                // 做點事情
                try {
                    Thread.sleep(100);
                    if(System.currentTimeMillis() % 3 == 0 ){
                         System.out.println("stop!");
                         throw  new RuntimeException("break!"); //(1)注釋掉這一行將只有兩個Thread!
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(name + " said:" + i+" Thread="+Thread.currentThread().getName());
            }
        }
    }

    
    public static void main(String[] args) {
        // 創(chuàng)建線程池
//        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        ExecutorService threadPool = Executors.newFixedThreadPool(2);
//        ExecutorService threadPool = Executors.newCachedThreadPool();

        
        // 向線程池里面扔任務
        for (int i = 0; i < 10; i++) {
            threadPool.execute(new MyTask("Task" + i));
        }

        
        // 關閉線程池
        threadPool.shutdown();
    }
}

注釋掉(1)處的異常會得到正常結果

Task0 said:0 Thread=pool-1-thread-1
Task1 said:0 Thread=pool-1-thread-2
Task0 said:1 Thread=pool-1-thread-1
Task1 said:1 Thread=pool-1-thread-2
Task2 said:0 Thread=pool-1-thread-1
Task3 said:0 Thread=pool-1-thread-2
Task2 said:1 Thread=pool-1-thread-1
Task3 said:1 Thread=pool-1-thread-2
......

任務將在thread 1和2之間切換
拋出異常RuntimeException會看到如下的情況:

.......
java.lang.RuntimeException: break!
    at ThreadPoolTest1$MyTask.run(ThreadPoolTest1.java:22)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Task4 said:0 Thread=pool-1-thread-5
Task5 said:0 Thread=pool-1-thread-6
......

能看到線程池在不斷創(chuàng)建新的線程.