背景

對于每隔幾毫秒發生的事件，最好使每個事件的開銷較低（小于一毫秒）。?否則，對性能的影響將很大。?記錄事件意味著你將向磁盤寫入內容。?如果磁盤不夠快，你將丟失事件。?你需要一個解決方案，而不是記錄事件本身。

在處理大量事件時，了解每個事件的度量值也無濟于事。?大多數時候，你只需要一些統計信息。?因此，你可以在進程本身中獲取統計信息，然后偶爾編寫一個事件來報告統計信息，這是 EventCounter 將執行的操作。

代碼實現

下面是有關如何實現 System.Diagnostics.Tracing.EventSource 的示例。?創建名為 MinimalEventCounterSource.cs 的新文件

using System; using System.Collections.Generic; using System.Linq; using System.Threading.Tasks; using System.Diagnostics.Tracing;namespace WebApplication42 {[EventSource(Name = "Sample.EventCounter.Minimal")]public sealed class MinimalEventCounterSource : EventSource{public static readonly MinimalEventCounterSource Log = new MinimalEventCounterSource();private EventCounter _requestCounter;private MinimalEventCounterSource() =>_requestCounter = new EventCounter("request-time", this){DisplayName = "Request Processing Time",DisplayUnits = "ms"};public void Request(string url, float elapsedMilliseconds){Console.WriteLine("url:" + url + " elapsedMilliseconds:" + elapsedMilliseconds);WriteEvent(1, url, elapsedMilliseconds);_requestCounter?.WriteMetric(elapsedMilliseconds);}protected override void Dispose(bool disposing){_requestCounter?.Dispose();_requestCounter = null;base.Dispose(disposing);}} }

添加操作篩選器，創建名為 LogRequestTimeFilterAttribute.cs 的新文件，并使用以下代碼：

using Microsoft.AspNetCore.Http.Extensions; using Microsoft.AspNetCore.Mvc.Filters; using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using System.Threading.Tasks;namespace WebApplication42 {public class LogRequestTimeFilterAttribute : ActionFilterAttribute{private readonly Stopwatch _stopwatch = new Stopwatch();public override void OnActionExecuting(ActionExecutingContext context) => _stopwatch.Start();public override void OnActionExecuted(ActionExecutedContext context){_stopwatch.Stop();MinimalEventCounterSource.Log.Request(context.HttpContext.Request.GetDisplayUrl(), _stopwatch.ElapsedMilliseconds);}} }

操作篩選器在請求開始時啟動 Stopwatch，并在其完成后停止，捕獲運行時間。?總毫秒數記錄到 MinimalEventCounterSource 單一實例。?為了應用此篩選器，需要將其添加到篩選器集合。?在 Startup.cs 文件中，更新包含此篩選器的 ConfigureServices 方法。

// This method gets called by the runtime. Use this method to add services to the container.public void ConfigureServices(IServiceCollection services){services.AddControllers(options => options.Filters.Add<LogRequestTimeFilterAttribute>());services.AddSwaggerGen(c =>{c.SwaggerDoc("v1", new OpenApiInfo { Title = "WebApplication42", Version = "v1" });});}

url:https://localhost:5008/WeatherForecast elapsedMilliseconds:70 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:19 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:18 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:19 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:22 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:17 url:https://localhost:5008/WeatherForecast elapsedMilliseconds:17

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