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c# - 在 Azure IoTEdge 的模块中启动长时间运行方法的最佳方式是什么？

问题描述

只要设备正在运行，我就需要保持活动功能。该方法位于模块内部。我遇到它在 3-10 小时后停止运行。

// Async method to send keepalive signals
private static async void SendKeepaliveToCloudMessagesAsync()
{
    int keep_alive_counter = 0;
    while (true)
    {
        try
        {
            String timestamp = DateTimeOffset.UtcNow.ToString("u");
            String activity_type = "Device-Keepalive";
            // Create JSON message
            var telemetryDataPoint = new
            {
                timestamp,
                activity_type,
                device_id,
                keep_alive_counter
            };
            var messageString = JsonConvert.SerializeObject(telemetryDataPoint);
            var message = new Message(Encoding.ASCII.GetBytes(messageString));
            keep_alive_counter++;

            // Add a custom application property to the message.
            // An IoT hub can filter on these properties without access to the message body.
            message.Properties.Add("keepaliveAlert", (keep_alive_counter < 30) ? "true" : "false");

            // Send the telemetry message
            await s_deviceClient.SendEventAsync(message);
            Console.WriteLine("[{0}] > Sending Keepalive message: {1}", DateTimeOffset.UtcNow.ToString("u"), messageString);

            await Task.Delay(s_keepaliveInterval * 1000);
        }
        catch (Exception ex)
        {
            Console.Error.WriteLine("Send keepalive Failed! {0}", ex);
        }
    }
}

上面的代码工作正常，3-10 小时，但突然停止，我没有收到 IoTHub 上的保持活动消息。

我设法从日志中得到以下消息：

Send keepalive Failed! System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'IoT Client'.
   at Microsoft.Azure.Devices.Client.Transport.DefaultDelegatingHandler.ThrowIfDisposed()
   at Microsoft.Azure.Devices.Client.Transport.DefaultDelegatingHandler.OpenAsync(CancellationToken cancellationToken)
   at Microsoft.Azure.Devices.Client.Transport.RetryDelegatingHandler.<>c__DisplayClass32_0.<<OpenAsyncInternal>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.Azure.Devices.Client.Transport.RetryDelegatingHandler.EnsureOpenedAsync(CancellationToken cancellationToken)
   at Microsoft.Azure.Devices.Client.Transport.RetryDelegatingHandler.<>c__DisplayClass14_0.<<SendEventAsync>b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.Azure.Devices.Client.Transport.RetryDelegatingHandler.SendEventAsync(Message message, CancellationToken cancellationToken)
   at Microsoft.Azure.Devices.Client.InternalClient.SendEventAsync(Message message)
   at MotionDetection.Program.SendKeepaliveToCloudMessagesAsync() in /app/Program.cs:line 439

标签： c#azure-iot-edge

解决方案

虽然您看到的错误不应该发生，但我仍然可以回答实际问题：

您构建模块以无限时间发送消息的方式看起来不错，并且通常应该可以工作。实际上，官方 repo 中的 IoT Edge 团队的样本之一与您的非常相似，请参见此处（对于 case when SendUnlimitedMessages()is true）。

Maybe just follow their example and implement a shutdown handler as well for a clean exit strategy.

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