[英]Cancel long running operation on client cancel
I started my first project with asp.net core and razor pages. 我从asp.net核心和剃须刀页面开始了我的第一个项目。 On a client request, a long running database operation will be started.
应客户请求,将启动长时间运行的数据库操作。 Now i want to recognize, when the user leaves the website, so the database operation can be cancelled.
现在我想知道,当用户离开网站时,可以取消数据库操作。
I've tried it with a cancellationToken, but it will never be cancelled. 我已经使用了cancelToken进行了尝试,但是它永远不会被取消。
public async Task<JsonResult> OnPostReadAsync([DataSourceRequest] DataSourceRequest request, CancellationToken cancellationToken)
{
var messages = await _logMessageService.GetLogMessagesAsync(request, cancellationToken);
return new JsonResult(messages.ToDataSourceResult(request));
}
The function get called by an Telerik Kendo UI Grid. 该功能由Telerik Kendo UI网格调用。 Can you tell me, why the cancellation token don't get cancelled, or what other options I have to detect a abortion by the client?
您能告诉我,为什么取消令牌没有被取消,或者我还必须通过其他哪些选项来检测客户端是否中止?
Edit 1 编辑1
I pass the Token through to this function call of a NpgsqlCommand: 我将令牌传递给NpgsqlCommand的此函数调用:
var dataReader = await command.ExecuteReaderAsync(cancellationToken);
To cancel IO bound ie task which is running long , following is code that you can do which i got form the C# with CLR book. 要取消IO绑定,即运行时间长的任务,下面是您可以执行的代码,这些代码是我用CLR书从C#中获得的。
Design extension method for task as below. 设计任务扩展方法如下。
private static async Task<TResult> WithCancellation<TResult>(this Task<TResult> originalTask,
CancellationToken ct) {
// Create a Task that completes when the CancellationToken is canceled
var cancelTask = new TaskCompletionSource<Void>();
// When the CancellationToken is canceled, complete the Task
using (ct.Register(
t => ((TaskCompletionSource<Void>)t).TrySetResult(new Void()), cancelTask)) {
// Create a Task that completes when either the original or
// CancellationToken Task completes
Task any = await Task.WhenAny(originalTask, cancelTask.Task);
// If any Task completes due to CancellationToken, throw OperationCanceledException
if (any == cancelTask.Task) ct.ThrowIfCancellationRequested();
}
// await original task (synchronously); if it failed, awaiting it
// throws 1st inner exception instead of AggregateException
return await originalTask;
}
as given in following example code you can cancel it by using extension method designed above. 如以下示例代码所示,您可以使用上面设计的扩展方法将其取消。
public static async Task Go() {
// Create a CancellationTokenSource that cancels itself after # milliseconds
var cts = new CancellationTokenSource(5000); // To cancel sooner, call cts.Cancel()
var ct = cts.Token;
try {
// I used Task.Delay for testing; replace this with another method that returns a Task
await Task.Delay(10000).WithCancellation(ct);
Console.WriteLine("Task completed");
}
catch (OperationCanceledException) {
Console.WriteLine("Task cancelled");
}
}
In this example cancellation done based on given time , but you can call cancellation by calling cancel method. 在此示例中,取消是基于给定的时间完成的,但是您可以通过调用cancel方法来调用取消。
So I found the answer myself after some more research. 因此,经过更多研究,我自己找到了答案。 The problem is a bug in IISExpress as mentioned here: https://github.com/aspnet/Mvc/issues/5239#issuecomment-323567952
问题是这里提到的IISExpress中的错误: https : //github.com/aspnet/Mvc/issues/5239#issuecomment-323567952
I switched to Kestrel and now everything works as expected. 我切换到Kestrel,现在一切正常。
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