单进程阻塞队列

Question

我正在编写一个与硬件通信的应用程序。虽然应用程序可以同时并行接收和处理多个请求，但硬件不能！

硬件要求这些并行请求基本上组织成一个线性请求链，每个请求一个接一个地执行。

我还需要能够对请求进行优先级排序，因为有些是不紧急的后台进程，有些是活动的，需要跳到队列的前面以便立即处理。

我对队列没有太多经验，但是如果这样的库还不存在，我会感到惊讶。

Answer 1

见https://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html

我建议对您的请求使用包装器，该包装器具有专门针对此队列的优先级值。例如，您可以使用 Long 作为该值，计算

value = timestamp % N * priorityLevel

N 取决于您处理事件需要多长时间

priorityLevel 值越低表示越紧急（大于零）

编辑：在评论中说明后

您似乎需要创建实例 ThreadPoolExecutor 并将您自己的队列传递给它，该队列将是 PriorityBlockingQueue. Task you put into this pool need to implement Comparable 的实例，它将按执行优先级对它们进行排序。

见一点old reference，但作为灵感应该足够了。

编辑：建议的优先级函数对于较小的 N 是危险的，现在看数字，long 可以在溢出发生之前乘以很多，所以将模数排除在外将无济于事更少，特别是如果你只有两个优先级（抱歉神秘化）

编辑：实施建议的解决方案

import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class QTest {
    public static void main(String[] args){
        //create executor with exactly one thread (first four arguments) that is
        //using priority queue to store tasks (it takes care of sorting by priority)
        ThreadPoolExecutor executor = new ThreadPoolExecutor(1, 1, 0, TimeUnit.MILLISECONDS, new PriorityBlockingQueue());
        executor.execute(new EventWrapper(1, "A"));
        executor.execute(new EventWrapper(2, "B"));
        executor.execute(new EventWrapper(1, "C"));
        executor.execute(new EventWrapper(3, "D"));
        executor.execute(new EventWrapper(1, "E"));
        //just to have it terminated once test is done
        executor.shutdown();
    }
}

//in this wrapper should be loaded anything you want to have executed
class EventWrapper implements Comparable<EventWrapper>, Runnable{
    public final long priority;
    //name just to recognize what is being executed
    public final String name;
    public EventWrapper(int priority, String name){
        //priority function out of current time, can be obviously inserted from elsewhere
        this.priority = priority*System.currentTimeMillis();
        this.name = name;
    }

    @Override
    public int compareTo(EventWrapper that) {
        //lower priority first
        if(this.priority==that.priority)return 0;
        return this.priority>that.priority?1:-1;
    }

    @Override
    public void run() {
        System.out.println("Executing task "+name+" with priority "+priority);
        //sleep to rule out speed of insertion in executor
        try {Thread.sleep(1000);
        } catch (InterruptedException ex) {}
    }
}

创建任务的结果是

Executing task A with priority 1433276819484
Executing task C with priority 1433276819485
Executing task E with priority 1433276819485
Executing task B with priority 2866553638970
Executing task D with priority 4299830458455

Answer 2

如果您已经熟悉 PriorityBlockingQueue，为什么不简单地轮询它来处理硬件请求？

public class HardwareHandler

    public static final PriorityBlockingQueue<Message> queue = 
        new PriorityBlockingQueue<Message>();

    static {
        while (true) {
            Message m = queue.take();
            handleMessage(m);
        }
    }

    private static void handleMessage(Message m) {
        // handle message....
    }
}

Answer 3

根据所有有用的评论和答案，我确定可能没有针对此问题的预构建解决方案。为了尝试对问题提供全面的答案，我尝试使用 PriorityBlockingQueue.

编写自己的实现

我在 StackExchange Code Review 上发布了代码，您可以看到完整的代码和任何社区建议的改进。

See answer on code review

单进程阻塞队列

Single process blocking queue

java

queue

priority-queue

message-queue