无法在 RejectionHandler 中获取 CallableThread

Question

我有线程池，它将使用 Callable 个工作线程和 RejectionHandler。我需要在 RejectionHandler 中获取此 Callable 任务，但无法获取它。

在下面的示例中，我需要为其执行 RejectionHandler 的 Callable 任务的 uniqueId。在 RejecitonHandler 中，Runnable 被强制转换为 FutureTask，我希望它应该被强制转换为 Callable 工作线程。

请帮助我在 RejectionHandler 中获取 Callable 工作线程实例。

import java.util.Random;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.FutureTask;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class RejectionDemo {
    RejectionDemo(){
        Random random = new Random();
        ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 1, 1, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(2), new RejectionHandlerImpl());
        CallableWorkerThread workers[] = 
                new CallableWorkerThread[10];
        for (int i=0; i< workers.length; i++){
            workers[i] = new CallableWorkerThread(random.nextInt(100));
            FutureTask<Integer> task = new FutureTask<Integer>(workers[i]);
            executor.submit(task);
        }
    }

    public static void main(String args[]){
        RejectionDemo demo = new RejectionDemo();
    }
    public class CallableWorkerThread implements
        Callable<Integer> {
        private int uniqueId;

        CallableWorkerThread(int uniqueId) {
            this.uniqueId = uniqueId;
        }

        public Integer call() {
            System.out.println("Unique id="+uniqueId);
            return uniqueId;
        }
        public String toString(){
            return ""+uniqueId;
        }
    }
    class RejectionHandlerImpl implements RejectedExecutionHandler{
        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
            try{
                System.out.println(r);
            }catch(Throwable t){
                t.printStackTrace();
            }
        }
    }
}

输出

java.util.concurrent.FutureTask@70036428
Unique id=68
java.util.concurrent.FutureTask@6ea4b78b
java.util.concurrent.FutureTask@e3f6d
java.util.concurrent.FutureTask@1ce84763
java.util.concurrent.FutureTask@55a6c368
java.util.concurrent.FutureTask@4e77b794
java.util.concurrent.FutureTask@15b57dcb
Unique id=55
Unique id=83

我期待 CallableWorkerThread 而不是 FutureTask。帮助我获取 WorkerThread 实例。

Answer 1

在你的代码中

workers[i] = new CallableWorkerThread(random.nextInt(100));
FutureTask<Integer> task = new FutureTask<Integer>(workers[i]);
executor.submit(task);

你创建了一个 FutureTask 来包装 CallableWorkerThread 实例但是你正在使用 submit 它接受任意 Runnable 和 returns 一个 FutureTask 包装 Runnable.

换句话说，您将 FutureTask 包裹在另一个 FutureTask 中。有两种方法可以解决这个问题

使用

workers[i] = new CallableWorkerThread(random.nextInt(100));
executor.submit(workers[i]);

让 ExecutorService 将您的 Callable 包裹在 FutureTask 中。

使用

workers[i] = new CallableWorkerThread(random.nextInt(100));
executor.execute(new FutureTask<Integer>(workers[i]));

手动包装 Callable 并将其作为 Runnable 入队而不进一步包装（注意使用 execute 而不是 submit）

由于您想启用对原始 Callable 的检索，第二个选项适合您，因为它使您可以完全控制 FutureTask 实例：

static class MyFutureTask<T> extends FutureTask<T> {
    final Callable<T> theCallable;

    public MyFutureTask(Callable<T> callable) {
        super(callable);
        theCallable=callable;
    }
}

提交代码：

    for (int i=0; i< workers.length; i++){
        workers[i] = new CallableWorkerThread(random.nextInt(100));
        executor.execute(new MyFutureTask<Integer>(workers[i]));
    }

拒绝执行处理程序：

class RejectionHandlerImpl implements RejectedExecutionHandler{
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        if(r instanceof MyFutureTask) {
            MyFutureTask<?> myFutureTask = (MyFutureTask)r;
            Callable<?> c=myFutureTask.theCallable;
            System.out.println(c);
        }
        else System.out.println(r);
    }
}

无法在 RejectionHandler 中获取 CallableThread

Unable to get CallableThread in RejectionHandler

java

concurrency

multithreading

threadpoolexecutor

输出