Thread safety issue

[Guest]

In my VB.Net ASP project, I have a function in a module (same thing as a
static function in C#'s terms) that is shared by all the sessions. What is
does once called is to write messages into a common log file that's also
shared by all the sessions. To make sure it is thread safe, I use the Monitor
class to sync it up. Here is the simplified version of that function"

Public Sub WriteLog(ByVal strMsg As String)
Dim oWriter As StreamWriter
Dim strLogPath As String = "C:\Logs\test.log"

If Not File.Exists(strLogPath) Then
oWriter = File.CreateText(strLogPath)
Else
oWriter = File.AppendText(strLogPath)
End If

Monitor.Enter(oWriter)
Try
oWriter.WriteLine(strMsg)
oWriter.Flush()
oWriter.Close()
Finally
Monitor.Exit(oWriter)
End Try
End Sub

My problem is that this code doesn't seem to do what I want it to do. I am
still getting error that says "The process cannot access the file
'C:\Logs\test.log' because it is used by another process.". Why is this
happening? I must be doing something wrong. Can some one tell me how I should
do this?

Thanks a million!

Feng

 

[Bruce Barker]

the object you are locking on is local to the call, so threads do not block
each other because they are all locking different objects.

you need to lock on a static object. you could use the class type, but there
is a performance hit for this, better to create an actual object to lock on.
also the File.Exists need to be in lock.

-- bruce (sqlwork.com)