ASP.NET Shared variable for an Error Handler

Question

I am planning to use a shared variable to implement a logging facility. Have a look at the code below:

Imports System.IO

Public Class TestClass

    Public Shared objError As New StreamWriter("C:\Test.txt")

End Class

 Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Try
            TestClass.objError.WriteLine("Error 1")
            TestClass.objError.WriteLine("Error 2")
            TestClass.objError.WriteLine("Error 3")
            'TestClass.objError.Close()
            TestClass.objError.WriteLine("Error 4")
            TestClass.objError = Nothing
        Catch ex As Exception

        End Try
    End Sub

I don't understand how this shared variable is created and destroyed (I assume it is created before the form_load and destroyed by the form_unload). I also don't understand why it is possible to set the reference to the static variable to Nothing; surely the variable should exist until the program ends? (Q1, part 1) I realise this is a simple question.

Is there a better way to implement a logging mechanism? (Q1 part 2). The logging mechanism writes errors and log entries.

UPDATE I think I have found my answer here: http://msdn.microsoft.com/en-us/library/z2cty7t8.aspx. "A static variable continues to exist and retains its most recent value. The next time your code calls the procedure, the variable is not reinitialized, and it still holds the latest value that you assigned to it. A static variable continues to exist for the lifetime of the class or module that it is defined in."

I am not convinced that this is the best way to create a logging facility. Therefore part 2 to my question is still open.

Steve · Accepted Answer · 2012-05-28 20:05:21Z

2

You're confusing between the area of memory reserved for the variable Public Shared objError and the instance of an object created and assigned to this area As New StreamWriter("C:\Test.txt").

When you declare the variable objError, the compiler reserves the memory required, but doesn't fill it with a valid value (an instance of an object).
Is the New command that initializes this area with an object instance of a StreamWriter.

When you assign to the variable the value Nothing you are wiping the instance of the StreamWriter (really I prefer to call explicitily Flush and Close), but you are not deleting the area of memory reserved for the Shared variable.

Regarding the log. You ask 'which is the best way' then the best method is to use an external component as you have been recommended. It will be very difficult to create a better logging system, log4net has been tried and tested, it's free and it is considered the best.

edited May 28, 2012 at 20:05

answered May 28, 2012 at 19:48

Steve

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3 Comments

w0051977 Over a year ago

Thanks. It is very clear now +1. One more question though before I answer; after calling StreamWriter.WriteLine the first time; the file is locked (if a shared variable is not used). Is there a way to release the file lock without closing the StreamWriter?

Steve Over a year ago

You could look here at MSDN the documentation on FileStream that allow control on the locking. However, remember that if you don't close the stream after the write, you may lose informations if the program crashes. (Saying goodbye to logging data).

w0051977 Over a year ago

Yes, it seems the key is to pass a FileStream to the StreamWriter. The FileStream can be shared.

Matthias Meid · Accepted Answer · 2012-05-28 19:50:28Z

1

As an answer to part 2 I recommend you to use log4net or any other logging framework. You can capture errors via the ASP.NET Health Monitoring too. Is it, however, not that much of an ordinary logging facility.

edited May 28, 2012 at 19:50

answered May 28, 2012 at 19:20

Matthias Meid

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3 Comments

w0051977 Over a year ago

I would prefer to avoid third party tools if possible.

Matthias Meid Over a year ago

Updated answer. I would consider using a third party logging tool, however. Depends on your requirements I guess.

w0051977 Over a year ago

Thanks. After further thought. I am going to consider this. +1.

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