Console.WriteLine sometimes throws the handle is invalid exception

Question

I have an Azure function which has this line of code:

Console.WriteLine("Name: " + list.Count());

This line sometimes throws this exception:

The handle is invalid.

at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor+d__26.MoveNext (Microsoft.Azure.WebJobs.Host, Version=3.0.34.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35: C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:352)
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor+d__18.MoveNext (Microsoft.Azure.WebJobs.Host, Version=3.0.34.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35: C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:108) Inner exception System.IO.IOException handled at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw: at System.ConsolePal+WindowsConsoleStream.Write (System.Console, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a) at System.IO.StreamWriter.Flush (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.IO.StreamWriter.WriteLine (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.IO.TextWriter+SyncTextWriter.WriteLine (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Console.WriteLine (System.Console, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)

Should we ignore this or don't use console class in Azure function?

Answer 1

This happens when the console window has been closed, or if the console output has been redirected to a file or other stream.

In azure functions, you should not use the Console.WriteLine . instead, you should use ILogger to write logs. you can write logs like log.LogInformation("Name: " + list.Count()); , this will write output to the Azure Functions runtime log. you can also view logs in the azure portal.

Edit : As @Fildor suggested in comment, you could use log.LogInformation("Name: {count}", list.Count());