c# – Service Fabric RunAsync(CancellationToken cancellationToken)不会被取消

我认为RunAsync方法将CancellationToken作为一个很好的参数.不幸的是,我的观察结果从未被取消.

当然,取消RunAsync方法并调用OnCloseAsync会有点多余.我仍然想知道取消实际发生的时间(如果).

我应该写一些额外的代码来在我的客户端提供一个工作的Stop()方法吗？我本来希望RunAsync中的cancellationToken实际上会被取消;-)

我的服务架构服务代码：

/// <summary>
/// This is the main entry point for your service instance.
/// </summary>
/// <param name="cancellationToken">Canceled when Service Fabric needs to shut down this service instance.</param>
protected override async Task RunAsync(CancellationToken cancellationToken)
{
    // TODO: Replace the following sample code with your own logic 
    //       or remove this RunAsync override if it's not needed in your service.

    long iterations = 0;

    while (!cancellationToken.IsCancellationRequested)
    {
        // I commented this out because I want my client to handle the cancellation 
        // event gracefully without throwing an OperationCanceled exception.
        //cancellationToken.ThrowIfCancellationRequested();

        // I never found these messages in any logs. Nor in the diagnostics events window in Visual Studio.
        ServiceEventSource.Current.ServiceMessage(this, "Working-{0}", ++iterations);

        await _client.Start(cancellationToken);

        await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken);
    }
}

我的示例客户端实现：

public class Client
{
    private static readonly Logger _logger = LogManager.GetCurrentClassLogger();

    public async Task Start(CancellationToken cancellationToken = default(CancellationToken))
    {
        while (!cancellationToken.IsCancellationRequested)
        {
            _logger.Info("Saying hello from Main Operation.");
            await Task.Delay(3000, cancellationToken);
        }

        _logger.Info("Cancellation requested. Shutting down MainOperation().");
    }

    public void Stop()
    {
        _logger.Info("Stop requested. But I have no means to stop. Not implemented.");
    }
}

解决方法:

是的,取消令牌实际上已取消.这是有保证的.我可以向你保证,经过多年的测试和生产使用,这不是一个疏忽.

但是,您的代码存在疏忽.

如果您希望从客户端看到此跟踪输出：

 _logger.Info("Cancellation requested. Shutting down MainOperation().");

你不会,更不可能你会看到它.为什么？因为之前这行：

await Task.Delay(3000, cancellationToken);

在延迟期间发出取消令牌信号时,将抛出OperationCanceledException.这将使您退出循环并退出RunAsync,因此您的日志记录行将不会执行.

由于您在该延迟中花费3秒,并且在循环中花费超过它的纳秒,您可以看到为什么当您不在延迟内时取消会发生的可能性极小.

标签：c,azure-service-fabric
来源： https://codeday.me/bug/20190608/1199082.html