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詳解C#如何實現(xiàn)一個事件總線

更新時間：2024年10月30日 09:03:11 作者：小碼編匠

Event Bus（事件總線）是一種用于在應(yīng)用程序內(nèi)部或跨應(yīng)用程序組件之間進(jìn)行事件通信的機(jī)制,它允許不同的組件通過發(fā)布和訂閱事件來進(jìn)行解耦和通信,本文給大家介紹了C# 如何實現(xiàn)一個事件總線,需要的朋友可以參考下

使用 C# 實現(xiàn)一個 Event Bus

Event Bus（事件總線）是一種用于在應(yīng)用程序內(nèi)部或跨應(yīng)用程序組件之間進(jìn)行事件通信的機(jī)制。

它允許不同的組件通過發(fā)布和訂閱事件來進(jìn)行解耦和通信。在給定的代碼片段中，我們可以看到一個使用C#實現(xiàn)的Event Bus。它定義了一些接口和類來實現(xiàn)事件的發(fā)布和訂閱。

首先，我們有兩個基本的約束接口：IEvent和IAsyncEventHandler<TEvent>。

IEvent是一個空接口，用于約束事件的類型。IAsyncEventHandler<TEvent>是一個泛型接口，用于約束事件處理程序的類型。它定義了處理事件的異步方法HandleAsync和處理異常的方法HandleException。接下來，我們有一個IEventBus接口，它定義了一些操作方法用于發(fā)布和訂閱事件。

其中，Publish<TEvent>和PublishAsync<TEvent>方法用于發(fā)布事件，而OnSubscribe<TEvent>方法用于訂閱事件。然后，我們看到一個實現(xiàn)了本地事件總線的類LocalEventBusManager<TEvent>。它實現(xiàn)了ILocalEventBusManager<TEvent>接口，用于在單一管道內(nèi)處理本地事件。它使用了一個Channel<TEvent>來存儲事件，并提供了發(fā)布事件的方法Publish和PublishAsync。此外，它還提供了一個自動處理事件的方法AutoHandle。

總的來說Event Bus提供了一種方便的方式來實現(xiàn)組件之間的松耦合通信。

通過發(fā)布和訂閱事件，組件可以獨立地進(jìn)行操作，而不需要直接依賴于彼此的實現(xiàn)細(xì)節(jié)。

這種機(jī)制可以提高代碼的可維護(hù)性和可擴(kuò)展性。

Github倉庫地址：https://github.com/DonPangPang/soda-event-bus

實現(xiàn)一些基本約束

先實現(xiàn)一些約束，實現(xiàn)IEvent約束事件，實現(xiàn)IAsyncEvnetHandler<TEvent> where TEvent:IEvent來約束事件的處理程序。

public interface IEvent
{

}

public interface IAsyncEventHandler<in TEvent> where TEvent : IEvent
{
    Task HandleAsync(IEvent @event);

    void HandleException(IEvent @event, Exception ex);
}

接下來規(guī)定一下咱們的IEventBus，會有哪些操作方法?；揪褪前l(fā)布和訂閱。

public interface IEventBus
{
    void Publish<TEvent>(TEvent @event) where TEvent : IEvent;
    Task PublishAsync<TEvent>(TEvent @event) where TEvent : IEvent;

    void OnSubscribe<TEvent>() where TEvent : IEvent;
}

實現(xiàn)一個本地事件總線

本地事件處理

本地事件的處理我打算采用兩種方式實現(xiàn)，一種是LocalEventBusManager即本地事件管理，第二種是LocalEventBusPool池化本地事件。

LocalEvnetBusManager

LocalEventBusManager主要在單一管道內(nèi)進(jìn)行處理，集中進(jìn)行消費。

public interface ILocalEventBusManager<in TEvent>where TEvent : IEvent
{
    void Publish(TEvent @event);
    Task PublishAsync(TEvent @event) ;
    
    void AutoHandle();
}

public class LocalEventBusManager<TEvent>(IServiceProvider serviceProvider):ILocalEventBusManager<TEvent>
    where TEvent: IEvent
{
    readonly IServiceProvider _servicesProvider = serviceProvider;

    private readonly Channel<TEvent> _eventChannel = Channel.CreateUnbounded<TEvent>();

    public void Publish(TEvent @event)
    {
        Debug.Assert(_eventChannel != null, nameof(_eventChannel) + " != null");
        _eventChannel.Writer.WriteAsync(@event);
    }

    private CancellationTokenSource Cts { get; } = new();

    public void Cancel()
    {
        Cts.Cancel();
    }
    
    public async Task PublishAsync(TEvent @event)
    {
        await _eventChannel.Writer.WriteAsync(@event);
    }

    public void AutoHandle()
    {
        // 確保只啟動一次
        if (!Cts.IsCancellationRequested) return;

        Task.Run(async () =>
        {
            while (!Cts.IsCancellationRequested)
            {
                var reader = await _eventChannel.Reader.ReadAsync();
                await HandleAsync(reader);
            }
        }, Cts.Token);
    }

    async Task HandleAsync(TEvent @event)
    {
        var handler = _servicesProvider.GetService<IAsyncEventHandler<TEvent>>();

        if (handler is null)
        {
            throw new NullReferenceException($"No handler for event {@event.GetType().Name}");
        }
        try
        {
            await handler.HandleAsync(@event);
        }
        catch (Exception ex)
        {
            handler.HandleException( @event, ex);
        }
    }
}

LocalEventBusPool

LocalEventBusPool即所有的Event都會有一個單獨的管道處理，單獨消費處理，并行能力更好一些。

public sealed class LocalEventBusPool(IServiceProvider serviceProvider)
{
    private readonly IServiceProvider _serviceProvider = serviceProvider;

    private class ChannelKey
    {
        public required string Key { get; init; }
        public int Subscribers { get; set; }

        public override bool Equals(object? obj)
        {
            if (obj is ChannelKey key)
            {
                return string.Equals(key.Key, Key, StringComparison.OrdinalIgnoreCase);
            }

            return false;
        }

        public override int GetHashCode()
        {
            return 0;
        }
    }

    private Channel<IEvent> Rent(string channel)
    {
        _channels.TryGetValue(new ChannelKey() { Key = channel }, out var value);

        if (value != null) return value;
        value = Channel.CreateUnbounded<IEvent>();
        _channels.TryAdd(new ChannelKey() { Key = channel }, value);
        return value;
    }

    private Channel<IEvent> Rent(ChannelKey channelKey)
    {
        _channels.TryGetValue(channelKey, out var value);
        if (value != null) return value;
        value = Channel.CreateUnbounded<IEvent>();
        _channels.TryAdd(channelKey, value);
        return value;
    }

    private readonly ConcurrentDictionary<ChannelKey, Channel<IEvent>> _channels = new();

    private CancellationTokenSource Cts { get; } = new();

    public void Cancel()
    {
        Cts.Cancel();
        _channels.Clear();
        Cts.TryReset();
    }

    public async Task PublishAsync<TEvent>(TEvent @event) where TEvent : IEvent
    {
        await Rent(typeof(TEvent).Name).Writer.WriteAsync(@event);
    }

    public void Publish<TEvent>(TEvent @event) where TEvent : IEvent
    {
        Rent(typeof(TEvent).Name).Writer.TryWrite(@event);
    }

    public void OnSubscribe<TEvent>() where TEvent : IEvent
    {
        var channelKey = _channels.FirstOrDefault(x => x.Key.Key == typeof(TEvent).Name).Key ??
                         new ChannelKey() { Key = typeof(TEvent).Name };
        channelKey.Subscribers++;

        Task.Run(async () =>
        {
            try
            {
                while (!Cts.IsCancellationRequested)
                {
                    var @event = await ReadAsync(channelKey);

                    var handler = _serviceProvider.GetService<IAsyncEventHandler<TEvent>>();
                    if (handler == null) throw new NullReferenceException($"No handler for Event {typeof(TEvent).Name}");
                    try
                    {
                        await handler.HandleAsync((TEvent)@event);
                    }
                    catch (Exception ex)
                    {
                        handler.HandleException((TEvent)@event, ex);
                    }
                }
            }
            catch (Exception e)
            {
                throw new InvalidOperationException("Error on onSubscribe handler", e);
            }
        }, Cts.Token);
    }

    private async Task<IEvent> ReadAsync(string channel)
    {
        return await Rent(channel).Reader.ReadAsync(Cts.Token);
    }

    private async Task<IEvent> ReadAsync(ChannelKey channel)
    {
        return await Rent(channel).Reader.ReadAsync(Cts.Token);
    }
}

LocalEventBus

實現(xiàn)LocalEventBus繼承自IEventBus即可，如果有需要擴(kuò)展的方法自行添加，池化和管理器的情況單獨處理。

public interface ILocalEventBus: IEventBus
{

}
public class LocalEventBus(IServiceProvider serviceProvider, LocalEventBusOptions options) : ILocalEventBus
{
    private  LocalEventBusPool? EventBusPool => serviceProvider.GetService<LocalEventBusPool>();
    
    
    public void Publish<TEvent>(TEvent @event) where TEvent : IEvent
    {
        if (options.Pool)
        {
            Debug.Assert(EventBusPool != null, nameof(EventBusPool) + " != null");
            EventBusPool.Publish(@event);
        }
        else
        {
            var manager = serviceProvider.GetService<LocalEventBusManager<TEvent>>();
            if (manager is null) throw new NullReferenceException($"No manager for event {typeof(TEvent).Name}, please add singleton service it.");
            manager.Publish(@event);
        }
    }

    public async Task PublishAsync<TEvent>(TEvent @event) where TEvent : IEvent
    {
        if (options.Pool)
        {
            Debug.Assert(EventBusPool != null, nameof(EventBusPool) + " != null");
            await EventBusPool.PublishAsync(@event);
        }
        else
        {
            var manager = serviceProvider.GetService<LocalEventBusManager<TEvent>>();
            if (manager is null) throw new NullReferenceException($"No manager for event {typeof(TEvent).Name}, please add singleton service it.");
            await manager.PublishAsync(@event);
        }
    }

    public void OnSubscribe<TEvent>() where TEvent : IEvent
    {
        if (options.Pool)
        {
            Debug.Assert(EventBusPool != null, nameof(EventBusPool) + " != null");
            EventBusPool.OnSubscribe<TEvent>();
        }
        else
        {
            var manager = serviceProvider.GetService<LocalEventBusManager<TEvent>>();
            if (manager is null) throw new NullReferenceException($"No manager for event {typeof(TEvent).Name}, please add singleton service it.");
            manager.AutoHandle();
        }
    }
}