java - ThreadFactory newThread() 方法对于 ThreadPoolExectutor 中的每个submit() 调用仅调用一次

Question

我试图为提交给 ThreadPoolExecutor 的每个 MyRunnable 分配一个编号，但没有成功。

我的代码片段:

import java.util.concurrent.*;

class SimpleThreadFactory implements ThreadFactory {
   String name;
   static int threadNo = 0;

   public SimpleThreadFactory (String name){
       this.name = name;
   }
   public Thread newThread(Runnable r) {
     ++threadNo;
     System.out.println("thread no:"+threadNo);
     return new Thread(r,name+":"+threadNo );
   }
   public static void main(String args[]){
        SimpleThreadFactory factory = new SimpleThreadFactory("Ravindra");
        ThreadPoolExecutor executor = new ThreadPoolExecutor(1,5,10,TimeUnit.SECONDS,new ArrayBlockingQueue(100),factory);
        for ( int i=0; i < 10; i++){
            executor.submit(new MyRunnable());
        }
        executor.shutdown();
    }
 }

 class MyRunnable implements Runnable {
     public void run(){
         System.out.println("Runnable:"+Thread.currentThread().getName());
     }
 }

我的期望:

executor.submit(new MyRunnable()); 应为执行器上的每个提交调用 ThreadFactory 中的 newThread。但实际上，这种事只发生过一次。

输出:

thread no:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1
Runnable:Ravindra:1

为什么submit()没有为每个提交的Runnable任务创建新线程？

如何为提交给执行器的每个 MyRunnable 分配序列号？

提前致谢

Answer 1

问题在于 CorePoolSize 和队列之间的交互。

来自Javadoc

"If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread."

和

"If there are more than corePoolSize but less than maximumPoolSize threads running, a new thread will be created only if the queue is full."

因此，目前，您的任务会排队，直到 CorePoolSize 中有空间(即当前正在执行的任务完成时)，因此当前您永远不会使用超过 1 个线程。