java - 指定 ThreadPoolExecutor 问题

Question

有没有什么方法可以创建至少有 5 个线程、最多 20 个线程和无限任务队列的执行器(意味着没有任务被拒绝)

我尝试了新的 ThreadPoolExecutor(5, 20, 60L, TimeUnit.SECONDS, queue) 我为队列想到的所有可能性:

new LinkedBlockingQueue() // never runs more than 5 threads
new LinkedBlockingQueue(1000000) // runs more than 5 threads, only when there is more than 1000000 tasks waiting
new ArrayBlockingQueue(1000000) // runs more than 5 threads, only when there is more than 1000000 tasks waiting
new SynchronousQueue() // no tasks can wait, after 20, they are rejected

没有一个能如愿以偿。

Answer 1

也许这样的事情对你有用？我刚把它搅起来，所以请戳一下。基本上，它实现了一个溢出线程池，用于提供底层 ThreadPoolExecutor

我看到它有两个主要缺点:

• submit() 上缺少返回的 Future 对象。但也许这对您来说不是问题。
• 辅助队列只会在提交作业时清空到ThreadPoolExecutor。必须有一个优雅的解决方案，但我还没有看到它。如果您知道 StusMagicExecutor 中会有稳定的任务流，那么这可能不是问题。 (“可能”是关键词。)一个选项可能是让您提交的任务在完成后戳 StusMagicExecutor？

斯图的魔法执行者:

public class StusMagicExecutor extends ThreadPoolExecutor {
    private BlockingQueue<Runnable> secondaryQueue = new LinkedBlockingQueue<Runnable>();  //capacity is Integer.MAX_VALUE.

    public StusMagicExecutor() {
        super(5, 20, 60L, SECONDS, new SynchronousQueue<Runnable>(true), new RejectionHandler());  
    }
    public void queueRejectedTask(Runnable task) {
        try {
            secondaryQueue.put(task);
        } catch (InterruptedException e) {
            // do something
        }
    }
    public Future submit(Runnable newTask) {
        //drain secondary queue as rejection handler populates it
        Collection<Runnable> tasks = new ArrayList<Runnable>();
        secondaryQueue.drainTo(tasks);

        tasks.add(newTask);

        for (Runnable task : tasks)
             super.submit(task);

        return null; //does not return a future!
    }
}

class RejectionHandler implements RejectedExecutionHandler {
    public void rejectedExecution(Runnable runnable, ThreadPoolExecutor executor) {
        ((StusMagicExecutor)executor).queueRejectedTask(runnable);
    }
}