System.Threading.Tasks.TaskCanceledException: 已取消一个任务

Exception: System.AggregateException: 发生一个或多个错误。 ---> System.Threading.Tasks.TaskCanceledException: 已取消一个任务。
System.Web.Http.Dispatcher.HttpRoutingDispatcher.SendAsync(System.Net.Http.HttpRequestMessage request, 
System.Threading.CancellationToken cancellationToken) > 
System.Net.Http.HttpMessageInvoker.SendAsync(System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) > 
System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsync(System.Net.Http.HttpRequestMessage request, 
System.Threading.CancellationToken cancellationToken) > System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start() > 
System.Web.Http.Dispatcher.HttpControllerDispatcher+d__1.MoveNext() > 
System.Web.Http.Controllers.ActionFilterResult.ExecuteAsync() > 
System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start() > 
System.Web.Http.Controllers.ActionFilterResult+d__2.MoveNext() > 
System.Web.Http.Controllers.ApiControllerActionInvoker.InvokeActionAsyncCore(System.Web.Http.Controllers.HttpActionContext actionContext, 
System.Threading.CancellationToken cancellationToken) > System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start() > 
System.Web.Http.Controllers.ApiControllerActionInvoker+d__0.MoveNext() > 
System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(System.Web.Http.Controllers.HttpControllerContext controllerContext, 
System.Collections.Generic.IDictionary`2[System.String,System.Object] arguments, System.Threading.CancellationToken cancellationToken) > 
System.Web.Http.Controllers.ReflectedHttpActionDescriptor+ActionExecutor+<>c__DisplayClass12.b__8(System.Object instance, System.Object[] methodParameters) > 
?.lambda_method(System.Runtime.CompilerServices.Closure , System.Object , System.Object[] ) > 

今天查看网站日志时，发现不少这种错误信息。

访问一个页面时，AJAX 请求 ASP.NET Web API 。多次点击刷新，出错。

原因：页面加载  =》 ajax 触发 web api =》  页面刷新 =》web api 的任务被取消 ;   web api 是异步编程, 任务取消时，会触发  AggregateException 导常。

日志记录时，遇到 AggregateException 时，直接忽略。