如何实现定时推送的具体方案

详细内容

详细内容大概分为4个部分，1.应用场景 2.遇到问题 3.设计 4.实现 5.运行效果

1.应用场景

需要定时推送数据，且轻量化的实现。

2.遇到问题

• 如果启动一个定时器去定时轮询
• （1）轮询效率比较低
• （2）每次扫库，已经被执行过记录，仍然会被扫描（只是不会出现在结果集中），会做重复工作
• （3）时效性不够好，如果每小时轮询一次，最差的情况下会有时间误差
• 如何利用“延时消息”，对于每个任务只触发一次，保证效率的同时保证实时性，是今天要讨论的问题。

3.设计

高效延时消息，包含两个重要的数据结构：

1. 环形队列，例如可以创建一个包含3600个slot的环形队列（本质是个数组）
2. 任务集合，环上每一个slot是一个Set

同时，启动一个timer，这个timer每隔1s，在上述环形队列中移动一格，有一个Current Index指针来标识正在检测的slot。

Task结构中有两个很重要的属性：

1. Cycle-Num：当Current Index第几圈扫描到这个Slot时，执行任务
2. Task-Function：需要执行的任务指针

假设当前Current Index指向第一格，当有延时消息到达之后，例如希望3610秒之后，触发一个延时消息任务，只需：

1. 计算这个Task应该放在哪一个slot，现在指向1，3610秒之后，应该是第11格，所以这个Task应该放在第11个slot的Set中
2. 计算这个Task的Cycle-Num，由于环形队列是3600格（每秒移动一格，正好1小时），这个任务是3610秒后执行，所以应该绕3610/3600=1圈之后再执行，于是Cycle-Num=1

Current Index不停的移动，每秒移动到一个新slot，这个slot中对应的Set，每个Task看Cycle-Num是不是0：

1. 如果不是0，说明还需要多移动几圈，将Cycle-Num减1
2. 如果是0，说明马上要执行这个Task了，取出Task-Funciton执行（可以用单独的线程来执行Task），并把这个Task从Set中删除

使用了“延时消息”方案之后，“订单48小时后关闭评价”的需求，只需将在订单关闭时，触发一个48小时之后的延时消息即可：

1. 无需再轮询全部订单，效率高
2. 一个订单，任务只执行一次
3. 时效性好，精确到秒（控制timer移动频率可以控制精度）

4.实现

首先写一个方案要理清楚自己的项目结构，我做了如下分层。

Interfaces ， 这层里主要约束延迟消息队列的队列和消息任务行。

public interface IRingQueue<T>
{
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback</param>
    void Add(long delayTime,Action<T> action);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime">The specified task is executed after N seconds.</param>
    /// <param name="action">Definitions of callback.</param>
    /// <param name="data">Parameters used in the callback function.</param>
    void Add(long delayTime, Action<T> action, T data);
    /// <summary>
    /// Add tasks [add tasks will automatically generate: task Id, task slot location, number of task cycles]
    /// </summary>
    /// <param name="delayTime"></param>
    /// <param name="action">Definitions of callback</param>
    /// <param name="data">Parameters used in the callback function.</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Add(long delayTime, Action<T> action, T data, long id);
    /// <summary>
    /// Remove tasks [need to know: where the task is, which specific task].
    /// </summary>
    /// <param name="index">Task slot location</param>
    /// <param name="id">Task ID, used when deleting tasks.</param>
    void Remove(long id);
    /// <summary>
    /// Launch queue.
    /// </summary>
    void Start();
}
 public interface ITask
 {
 }

Achieves，这层里实现之前定义的接口，这里写成抽象类是为了后面方便扩展。

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public abstract class BaseQueue<T> : IRingQueue<T>
{
    private long _pointer = 0L;
    private ConcurrentBag<BaseTask<T>>[] _arraySlot;
    private int ArrayMax;
    /// <summary>
    /// Ring queue.
    /// </summary>
    public ConcurrentBag<BaseTask<T>>[] ArraySlot
    {
        get { return _arraySlot ?? (_arraySlot = new ConcurrentBag<BaseTask<T>>[ArrayMax]); }
    }
    public BaseQueue(int arrayMax)
    {
        if (arrayMax < 60 && arrayMax % 60 == 0)
            throw new Exception("Ring queue length cannot be less than 60 and is a multiple of 60 .");
        ArrayMax = arrayMax;
    }
    public void Add(long delayTime, Action<T> action)
    {
        Add(delayTime, action, default(T));
    }
    public void Add(long delayTime,Action<T> action,T data)
    {
        Add(delayTime, action, data,0);
    }
    public void Add(long delayTime, Action<T> action, T data,long id)
    {
        NextSlot(delayTime, out long cycle, out long pointer);
        ArraySlot[pointer] =  ArraySlot[pointer] ?? (ArraySlot[pointer] = new ConcurrentBag<BaseTask<T>>());
        var baseTask = new BaseTask<T>(cycle, action, data,id);
        ArraySlot[pointer].Add(baseTask);
    }
    /// <summary>
    /// Remove tasks based on ID.
    /// </summary>
    /// <param name="id"></param>
    public void Remove(long id)
    {
        try
        {
            Parallel.ForEach(ArraySlot, (ConcurrentBag<BaseTask<T>> collection, ParallelLoopState state) =>
            {
                var resulTask = collection.FirstOrDefault(p => p.Id == id);
                if (resulTask != null)
                {
                    collection.TryTake(out resulTask);
                    state.Break();
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
    }
    public void Start()
    {
        while (true)
        {
            RightMovePointer();
            Thread.Sleep(1000);
            Console.WriteLine(DateTime.Now.ToString());
        }
    }
    /// <summary>
    /// Calculate the information of the next slot.
    /// </summary>
    /// <param name="delayTime">Delayed execution time.</param>
    /// <param name="cycle">Number of turns.</param>
    /// <param name="index">Task location.</param>
    private void NextSlot(long delayTime, out long cycle,out long index)
    {
        try
        {
            var circle = delayTime / ArrayMax;
            var second = delayTime % ArrayMax;
            var current_pointer = GetPointer();
            var queue_index = 0L;
            if (delayTime - ArrayMax > ArrayMax)
            {
                circle = 1;
            }
            else if (second > ArrayMax)
            {
                circle += 1;
            }
            if (delayTime - circle * ArrayMax < ArrayMax)
            {
                second = delayTime - circle * ArrayMax;
            }
            if (current_pointer + delayTime >= ArrayMax)
            {
                cycle = (int)((current_pointer + delayTime) / ArrayMax);
                if (current_pointer + second - ArrayMax < 0)
                {
                    queue_index = current_pointer + second;
                }
                else if (current_pointer + second - ArrayMax > 0)
                {
                    queue_index = current_pointer + second - ArrayMax;
                }
            }
            else
            {
                cycle = 0;
                queue_index = current_pointer + second;
            }
            index = queue_index;
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
    /// <summary>
    /// Get the current location of the pointer.
    /// </summary>
    /// <returns></returns>
    private long GetPointer()
    {
        return Interlocked.Read(ref _pointer);
    }
    /// <summary>
    /// Reset pointer position.
    /// </summary>
    private void ReSetPointer()
    {
        Interlocked.Exchange(ref _pointer, 0);
    }
    /// <summary>
    /// Pointer moves clockwise.
    /// </summary>
    private void RightMovePointer()
    {
        try
        {
            if (GetPointer() >= ArrayMax - 1)
            {
                ReSetPointer();
            }
            else
            {
                Interlocked.Increment(ref _pointer);
            }
            var pointer = GetPointer();
            var taskCollection = ArraySlot[pointer];
            if (taskCollection == null || taskCollection.Count == 0) return;
            Parallel.ForEach(taskCollection, (BaseTask<T> task) =>
            {
                if (task.Cycle > 0)
                {
                    task.SubCycleNumber();
                }
                if (task.Cycle <= 0)
                {
                    taskCollection.TryTake(out task);
                    task.TaskAction(task.Data);
                }
            });
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
            throw;
        }
    }
}
}
using System;
using System.Threading;
using DelayMessageApp.Interfaces;
namespace DelayMessageApp.Achieves.Base
{
public class BaseTask<T> : ITask
{
    private long _cycle;
    private long _id;
    private T _data;
    public Action<T> TaskAction { get; set; }
    public long Cycle
    {
        get { return Interlocked.Read(ref _cycle); }
        set { Interlocked.Exchange(ref _cycle, value); }
    }
    public long Id
    {
        get { return _id; }
        set { _id = value; }
    }
    public T Data
    {
        get { return _data; }
        set { _data = value; }
    }
    public BaseTask(long cycle, Action<T> action, T data,long id)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
        Id = id;
    }
    public BaseTask(long cycle, Action<T> action,T data)
    {
        Cycle = cycle;
        TaskAction = action;
        Data = data;
    }
    public BaseTask(long cycle, Action<T> action)
    {
        Cycle = cycle;
        TaskAction = action;
    }
    public void SubCycleNumber()
    {
        Interlocked.Decrement(ref _cycle);
    }
}
}

Logic，这层主要实现调用逻辑，调用者最终只需要关心把任务放进队列并指定什么时候执行就行了，根本不需要关心其它的任何信息。

public static void Start()
{
    //1.Initialize queues of different granularity.
    IRingQueue<NewsModel> minuteRingQueue = new MinuteQueue<NewsModel>();
    //2.Open thread.
    var lstTasks = new List<Task>
    {
        Task.Factory.StartNew(minuteRingQueue.Start)
    };
    //3.Add tasks performed in different periods.
    minuteRingQueue.Add(5, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Trump's visit to China！" });
    minuteRingQueue.Add(10, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Putin Pu's visit to China！" });
    minuteRingQueue.Add(60, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Eisenhower's visit to China！" });
    minuteRingQueue.Add(120, new Action<NewsModel>((NewsModel newsObj) =>
    {
        Console.WriteLine(newsObj.News);
    }), new NewsModel() { News = "Xi Jinping's visit to the US！" });
    //3.Waiting for all tasks to complete is usually not completed. Because there is an infinite loop.
    //F5 Run the program and see the effect.
    Task.WaitAll(lstTasks.ToArray());
    Console.Read();
}

Models，这层就是用来在延迟任务中带入的数据模型类而已了。自己用的时候换成任意自定义类型都可以。

5.运行效果

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