.NET 轻量级、高效任务调度器：ScheduleTask

郑子铭

发布于 2024-06-07 16:59:35

1760

发布于 2024-06-07 16:59:35

文章被收录于专栏：DotNet NB && CloudNative

前言

至于任务调度这个基础功能，重要性不言而喻，大多数业务系统都会用到,世面上有很多成熟的三方库比如Quartz，Hangfire，Coravel

这里我们不讨论三方的库如何使用而是从0开始自己制作一个简易的任务调度,如果只是到分钟级别的粒度基本够用。

正文

技术栈用到了:BackgroundService和NCrontab库

第一步我们定义一个简单的任务约定,不干别的就是一个执行方法:

public interface IScheduleTask
{
    Task ExecuteAsync();
}
public abstract class ScheduleTask : IScheduleTask
{
    public virtual Task ExecuteAsync()
    {
        return Task.CompletedTask;
    }
}

第二步定义特性标注任务执行周期等信的metadata

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = false)]
public class ScheduleTaskAttribute(string cron) : Attribute
{
    /// <summary>
    /// 支持的cron表达式格式 * * * * *：https://en.wikipedia.org/wiki/Cron
    /// 最小单位为分钟
    /// </summary>
    public string Cron { get; set; } = cron;
    public string? Description { get; set; }
    /// <summary>
    /// 是否异步执行.默认false会阻塞接下来的同类任务
    /// </summary>
    public bool IsAsync { get; set; } = false;
    /// <summary>
    /// 是否初始化即启动,默认false
    /// </summary>
    public bool IsStartOnInit { get; set; } = false;
}

第三步我们定义一个调度器约定,不干别的就是判断当前的任务是否可以执行:

public interface IScheduler
{
    /// <summary>
    /// 判断当前的任务是否可以执行
    /// </summary>
    bool CanRun(ScheduleTaskAttribute scheduleMetadata, DateTime referenceTime);
}

好了,基础步骤就完成了,如果我们需要实现配置级别的任务调度或者动态的任务调度那我们再抽象一个Store:

public class ScheduleTaskMetadata(Type scheduleTaskType, string cron)
{
    public Type ScheduleTaskType { get; set; } = scheduleTaskType;
    public string Cron { get; set; } = cron;
    public string? Description { get; set; }
    public bool IsAsync { get; set; } = false;
    public bool IsStartOnInit { get; set; } = false;
}
public interface IScheduleMetadataStore
{
    /// <summary>
    /// 获取所有ScheduleTaskMetadata
    /// </summary>
    Task<IEnumerable<ScheduleTaskMetadata>> GetAllAsync();
}

实现一个Configuration级别的Store

internal class ConfigurationScheduleMetadataStore(IConfiguration configuration) : IScheduleMetadataStore
{
    const string Key = "BiwenQuickApi:Schedules";

    public Task<IEnumerable<ScheduleTaskMetadata>> GetAllAsync()
    {
        var options = configuration.GetSection(Key).GetChildren();

        if (options?.Any() is true)
        {
            var metadatas = options.Select(x =>
            {
                var type = Type.GetType(x[nameof(ConfigurationScheduleOption.ScheduleType)]!);
                if (type is null)
                    throw new ArgumentException($"Type {x[nameof(ConfigurationScheduleOption.ScheduleType)]} not found!");

                return new ScheduleTaskMetadata(type, x[nameof(ConfigurationScheduleOption.Cron)]!)
                {
                    Description = x[nameof(ConfigurationScheduleOption.Description)],
                    IsAsync = string.IsNullOrEmpty(x[nameof(ConfigurationScheduleOption.IsAsync)]) ? false : bool.Parse(x[nameof(ConfigurationScheduleOption.IsAsync)]!),
                    IsStartOnInit = string.IsNullOrEmpty(x[nameof(ConfigurationScheduleOption.IsStartOnInit)]) ? false : bool.Parse(x[nameof(ConfigurationScheduleOption.IsStartOnInit)]!),
                };
            });
            return Task.FromResult(metadatas);
        }
        return Task.FromResult(Enumerable.Empty<ScheduleTaskMetadata>());
    }
}

然后，我们可能需要多任务调度的事件做一些操作或者日志存储。

比如失败了该干嘛,完成了回调其他后续业务等。

我们再来定义一下具体的事件IEvent,具体可以参考文章: https://www.cnblogs.com/vipwan/p/18184088

事件IEvent代码

1、首先定义一个事件约定的空接口

public interface IEvent{}

2、然后定义事件订阅者接口

public interface IEventSubscriber<T> where T : IEvent
{
    Task HandleAsync(T @event, CancellationToken ct);
    /// <summary>
    /// 执行排序
    /// </summary>
    int Order { get; }

    /// <summary>
    /// 如果发生错误是否抛出异常,将阻塞后续Handler
    /// </summary>
    bool ThrowIfError { get; }
}
public abstract class EventSubscriber<T> : IEventSubscriber<T> where T : IEvent
{
    public abstract Task HandleAsync(T @event, CancellationToken ct);
    public virtual int Order => 0;
    /// <summary>
    /// 默认不抛出异常
    /// </summary>
    public virtual bool ThrowIfError => false;
}

3、接着就是发布者

internal class Publisher(IServiceProvider serviceProvider)
{
 public async Task PublishAsync<T>(T @event, CancellationToken ct) where T : IEvent
 {
  var handlers = serviceProvider.GetServices<IEventSubscriber<T>>();
  if (handlers is null) return;
  foreach (var handler in handlers.OrderBy(x => x.Order))
  {
   try
   {
    await handler.HandleAsync(@event, ct);
   }
   catch
   {
    if (handler.ThrowIfError)
    {
     throw;
    }
    //todo:
   }
  }
 }
}

4、到此发布订阅的基本代码也就写完了.接下来就是注册发布者和所有的订阅者了

public abstract class ScheduleTaskEvent(IScheduleTask scheduleTask, DateTime eventTime) : IEvent
{
    /// <summary>
    /// 任务
    /// </summary>
    public IScheduleTask ScheduleTask { get; set; } = scheduleTask;
    /// <summary>
    /// 触发时间
    /// </summary>
    public DateTime EventTime { get; set; } = eventTime;
}
/// <summary>
/// 执行完成
/// </summary>
public sealed class TaskSuccessedEvent(IScheduleTask scheduleTask, DateTime eventTime, DateTime endTime) : ScheduleTaskEvent(scheduleTask, eventTime)
{
    /// <summary>
    /// 执行结束的时间
    /// </summary>
    public DateTime EndTime { get; set; } = endTime;
}
/// <summary>
/// 执行开始
/// </summary>
public sealed class TaskStartedEvent(IScheduleTask scheduleTask, DateTime eventTime) : ScheduleTaskEvent(scheduleTask, eventTime);
/// <summary>
/// 执行失败
/// </summary>
public sealed class TaskFailedEvent(IScheduleTask scheduleTask, DateTime eventTime, Exception exception) : ScheduleTaskEvent(scheduleTask, eventTime)
{
    /// <summary>
    /// 异常信息
    /// </summary>
    public Exception Exception { get; private set; } = exception;
}

接下来我们再实现基于NCrontab的简易调度器,这个调度器主要是解析Cron表达式判断传入时间是否可以执行ScheduleTask,具体的代码:

internal class SampleNCrontabScheduler : IScheduler
{
    /// <summary>
    /// 暂存上次执行时间
    /// </summary>
    private static ConcurrentDictionary<ScheduleTaskAttribute, DateTime> LastRunTimes = new();

    public bool CanRun(ScheduleTaskAttribute scheduleMetadata, DateTime referenceTime)
    {
        var now = DateTime.Now;
        var haveExcuteTime = LastRunTimes.TryGetValue(scheduleMetadata, out var time);
        if (!haveExcuteTime)
        {
            var nextStartTime = CrontabSchedule.Parse(scheduleMetadata.Cron).GetNextOccurrence(referenceTime);
            LastRunTimes.TryAdd(scheduleMetadata, nextStartTime);

            //如果不是初始化启动,则不执行
            if (!scheduleMetadata.IsStartOnInit)
                return false;
        }
        if (now >= time)
        {
            var nextStartTime = CrontabSchedule.Parse(scheduleMetadata.Cron).GetNextOccurrence(referenceTime);
            //更新下次执行时间
            LastRunTimes.TryUpdate(scheduleMetadata, nextStartTime, time);
            return true;
        }
        return false;
    }
}

然后就是核心的BackgroundService了，这里我用的IdleTime心跳来实现，粒度分钟，当然内部也可以封装Timer等实现更复杂精度更高的调度,这里就不展开讲了。

代码如下:

internal class ScheduleBackgroundService : BackgroundService
{
    private static readonly TimeSpan _pollingTime
DEBUG
      //轮询20s 测试环境下，方便测试。
      = TimeSpan.FromSeconds(20);
if
!DEBUG
     //轮询60s 正式环境下，考虑性能轮询时间延长到60s
     = TimeSpan.FromSeconds(60);
if
    //心跳10s.
    private static readonly TimeSpan _minIdleTime = TimeSpan.FromSeconds(10);
    private readonly ILogger<ScheduleBackgroundService> _logger;
    private readonly IServiceProvider _serviceProvider;
    public ScheduleBackgroundService(ILogger<ScheduleBackgroundService> logger, IServiceProvider serviceProvider)
    {
        _logger = logger;
        _serviceProvider = serviceProvider;
    }
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            var pollingDelay = Task.Delay(_pollingTime, stoppingToken);
            try
            {
                await RunAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                //todo:
                _logger.LogError(ex.Message);
            }
            await WaitAsync(pollingDelay, stoppingToken);
        }
    }
    private async Task RunAsync(CancellationToken stoppingToken)
    {
        using var scope = _serviceProvider.CreateScope();
        var tasks = scope.ServiceProvider.GetServices<IScheduleTask>();
        if (tasks is null || !tasks.Any())
        {
            return;
        }
        //调度器
        var scheduler = scope.ServiceProvider.GetRequiredService<IScheduler>();
        async Task DoTaskAsync(IScheduleTask task, ScheduleTaskAttribute metadata)
        {
            if (scheduler.CanRun(metadata, DateTime.Now))
            {
                var eventTime = DateTime.Now;
                //通知启动
                _ = new TaskStartedEvent(task, eventTime).PublishAsync(default);
                try
                {
                    if (metadata.IsAsync)
                    {
                        //异步执行
                        _ = task.ExecuteAsync();
                    }
                    else
                    {
                        //同步执行
                        await task.ExecuteAsync();
                    }
                    //执行完成
                    _ = new TaskSuccessedEvent(task, eventTime, DateTime.Now).PublishAsync(default);
                }
                catch (Exception ex)
                {
                    _ = new TaskFailedEvent(task, DateTime.Now, ex).PublishAsync(default);
                }
            }
        };
        //注解中的task
        foreach (var task in tasks)
        {
            if (stoppingToken.IsCancellationRequested)
            {
                break;
            }
            //标注的metadatas
            var metadatas = task.GetType().GetCustomAttributes<ScheduleTaskAttribute>();

            if (!metadatas.Any())
            {
                continue;
            }
            foreach (var metadata in metadatas)
            {
                await DoTaskAsync(task, metadata);
            }
        }
        //store中的scheduler
        var stores = _serviceProvider.GetServices<IScheduleMetadataStore>().ToArray();

        //并行执行,提高性能
        Parallel.ForEach(stores, async store =>
        {
            if (stoppingToken.IsCancellationRequested)
            {
                return;
            }
            var metadatas = await store.GetAllAsync();
            if (metadatas is null || !metadatas.Any())
            {
                return;
            }
            foreach (var metadata in metadatas)
            {
                var attr = new ScheduleTaskAttribute(metadata.Cron)
                {
                    Description = metadata.Description,
                    IsAsync = metadata.IsAsync,
                    IsStartOnInit = metadata.IsStartOnInit,
                };

                var task = scope.ServiceProvider.GetRequiredService(metadata.ScheduleTaskType) as IScheduleTask;
                if (task is null)
                {
                    return;
                }
                await DoTaskAsync(task, attr);
            }
        });
    }

    private static async Task WaitAsync(Task pollingDelay, CancellationToken stoppingToken)
    {
        try
        {
            await Task.Delay(_minIdleTime, stoppingToken);
            await pollingDelay;
        }
        catch (OperationCanceledException)
        {
        }
    }
}

最后收尾阶段我们老规矩扩展一下IServiceCollection:

internal static IServiceCollection AddScheduleTask(this IServiceCollection services)
{
    foreach (var task in ScheduleTasks)
    {
        services.AddTransient(task);
        services.AddTransient(typeof(IScheduleTask), task);
    }
    //调度器
    services.AddScheduler<SampleNCrontabScheduler>();
    //配置文件Store:
ices.AddScheduleMetadataStore<ConfigurationScheduleMetadataStore>();
    //BackgroundService
   services.AddHostedService<ScheduleBackgroundService>();
    return services;
}
/// <summary>
/// 注册调度器AddScheduler
/// </summary>
public static IServiceCollection AddScheduler<T>(this IServiceCollection services) where T : class, IScheduler
{
    services.AddSingleton<IScheduler, T>();
    return services;
}

/// <summary>
/// 注册ScheduleMetadataStore
/// </summary>
public static IServiceCollection AddScheduleMetadataStore<T>(this IServiceCollection services) where T : class, IScheduleMetadataStore
{
    services.AddSingleton<IScheduleMetadataStore, T>();
    return services;
}

老规矩我们来测试一下:

//通过特性标注的方式执行:
[ScheduleTask(Constants.CronEveryMinute)] //每分钟一次
[ScheduleTask("0/3 * * * *")]//每3分钟执行一次
public class KeepAlive(ILogger<KeepAlive> logger) : IScheduleTask
{
    public async Task ExecuteAsync()
    {
        //执行5s
        await Task.Delay(TimeSpan.FromSeconds(5));
        logger.LogInformation("keep alive!");
    }
}
public class DemoConfigTask(ILogger<DemoConfigTask> logger) : IScheduleTask
{
    public Task ExecuteAsync()
    {
        logger.LogInformation("Demo Config Schedule Done!");
        return Task.CompletedTask;
    }
}

通过配置文件的方式配置Store:

{
  "BiwenQuickApi": {
    "Schedules": [
      {
        "ScheduleType": "Biwen.QuickApi.DemoWeb.Schedules.DemoConfigTask,Biwen.QuickApi.DemoWeb",
        "Cron": "0/5 * * * *",
        "Description": "Every 5 mins",
        "IsAsync": true,
        "IsStartOnInit": false
      },
      {
        "ScheduleType": "Biwen.QuickApi.DemoWeb.Schedules.DemoConfigTask,Biwen.QuickApi.DemoWeb",
        "Cron": "0/10 * * * *",
        "Description": "Every 10 mins",
        "IsAsync": false,
        "IsStartOnInit": true
      }
    ]
  }
}

我们还可以实现自己的Store,这里以放到内存为例,如果有兴趣你可以可以自行开发一个面板管理:

public class DemoStore : IScheduleMetadataStore
{
    public Task<IEnumerable<ScheduleTaskMetadata>> GetAllAsync()
    {
        //模拟从数据库或配置文件中获取ScheduleTaskMetadata
        IEnumerable<ScheduleTaskMetadata> metadatas =
            [
                new ScheduleTaskMetadata(typeof(DemoTask),Constants.CronEveryNMinutes(2))
                {
                    Description="测试的Schedule"
                },
            ];
        return Task.FromResult(metadatas);
    }
}
//然后注册这个Store:
builder.Services.AddScheduleMetadataStore<DemoStore>();

所有的一切都大功告成,最后我们来跑一下Demo，成功了

当然这里是自己的固定思维设计的一个简约版,还存在一些不足,欢迎板砖轻拍指正!

提供同一时间单一运行中的任务实现

/// <summary>
/// 模拟一个只能同时存在一个的任务.一分钟执行一次,但是耗时两分钟.
/// </summary>
/// <param name="logger"></param>
[ScheduleTask(Constants.CronEveryMinute, IsStartOnInit = true)]
public class OnlyOneTask(ILogger<OnlyOneTask> logger) : OnlyOneRunningScheduleTask
{
    public override Task OnAbort()
    {
        logger.LogWarning($"[{DateTime.Now}]任务被打断.因为有一个相同的任务正在执行!");
        return Task.CompletedTask;
    }

    public override async Task ExecuteAsync()
    {
        var now = DateTime.Now;
        //模拟一个耗时2分钟的任务
        await Task.Delay(TimeSpan.FromMinutes(2));
        logger.LogInformation($"[{now}] ~ {DateTime.Now} 执行一个耗时两分钟的任务!");
    }
}