global variable defined in winforms not working as expected - vb.net

Question

I have a project in VB.Net that requires a global variable (a list of event log objects) throughout. This seemed simple enough, just define the variable and initialize in the Application's StartUp event, then access it throughout the application. Unfortunately, this only seems to work when there are no child processes (they have no access to the global variable) - so I'm way over my head as how to access the global variable from the child worker processes (if that is even possible).
The program starts several Test worker processes (that check multiple DB connections from different sources, remote web services from several sources, network checks, etc) w/ progress bars for each. If an error occurs during any of these tests, the error needs to be logged.
The problem is that, the program cannot log events to the Windows Event system because it won't be running under an administrator account (so logging there is not possible thanks to MS's decision to prevent logging under normal user accounts w/Vista,7,8,10), the program also can't log to a text file due to it being asynchronous and the file access contention problems (immediately logging an event to a text file won't work), so I wish to log any events/errors in memory (global variable), THEN dump it to a log file AFTER all child processes complete. Make any sense?
I created a class called AppEvent
Public Class AppEvent
Sub New()
EventTime_ = Date.Now
Level_ = EventLevel.Information
Description_ = String.Empty
Source_ = String.Empty
End Sub
Private EventTime_ As Date
Public Property EventTime() As Date
Get
Return EventTime_
End Get
Set(ByVal value As Date)
EventTime_ = value
End Set
End Property
Private Level_ As EventLevel
Public Property Level() As EventLevel
Get
Return Level_
End Get
Set(ByVal value As EventLevel)
Level_ = value
End Set
End Property
Private Description_ As String
Public Property Description() As String
Get
Return Description_
End Get
Set(ByVal value As String)
Description_ = value
End Set
End Property
Private Source_ As String
Public Property Source() As String
Get
Return Source_
End Get
Set(ByVal value As String)
Source_ = value
End Set
End Property
End Class
Public Enum EventLevel
[Information]
[Warning]
[Error]
[Critical]
[Fatal]
End Enum
And create a public variable just for this (and add an initial event to the AppEvents list)
Namespace My
Partial Friend Class MyApplication
'global variable here (using this for logging asynch call errors, then dumping this into a log file when all asynch calls are complete (due to file contention of log file)
Public AppEvents As New List(Of AppEvent)
Private Sub MyApplication_Startup(ByVal sender As Object, ByVal e As Microsoft.VisualBasic.ApplicationServices.StartupEventArgs) Handles Me.Startup
'create first event and add it to the global variable declared above
AppEvents.Add(New AppEvent With {.EventTime = Now, .Description = "Program Started", .Level = EventLevel.Information, .Source = "QBI"})
End Sub
End Class
End Namespace
Next, in my logging class, I have some methods for logging, flushing/writing the event(s)
Public Class AppLogging
Public Shared Sub WriteEventToAppLog(evt As AppEvent)
LogDataToFile(FormatLineItem(evt.EventTime, evt.Level, evt.Description, evt.Source))
End Sub
Public Shared Sub WriteEventsToAppLog(AppEvents As List(Of AppEvent))
Dim sbEvents As New StringBuilder
If AppEvents.Count > 0 Then
For Each evt In AppEvents
sbEvents.AppendLine(FormatLineItem(evt.EventTime, evt.Level, evt.Description, evt.Source))
Next
LogDataToFile(sbEvents.ToString.TrimEnd(Environment.NewLine))
End If
End Sub
Private Shared Function FormatLineItem(eventTime As Date, eventLevel As EventLevel, eventDescr As String, eventSource As String) As String
Return String.Format("Logged On: {0} | Level: {1} | Details: {2} | Source: {3}", eventTime, System.Enum.GetName(GetType(EventLevel), eventLevel).Replace("[", "").Replace("]", ""), eventDescr, eventSource)
End Function
Private Shared Sub LogDataToFile(eventLogText As String, Optional ByVal LogFileName As String = "Error.log", Optional ByVal HeaderLine As String = "****** Application Log ******")
'log file operations
Dim LogPath As String = System.AppDomain.CurrentDomain.BaseDirectory()
If Not LogPath.EndsWith("\") Then LogPath &= "\"
LogPath &= LogFileName
Dim fm As FileMode
Try
If System.IO.File.Exists(LogPath) Then
fm = FileMode.Append
Else
fm = FileMode.Create
eventLogText = HeaderLine & Environment.NewLine & eventLogText
End If
Using fs As New FileStream(LogPath, fm, FileAccess.Write)
Using sw As New StreamWriter(fs)
sw.WriteLine(eventLogText)
End Using
End Using
My.Application.AppEvents.Clear() 'clears the global var
Catch ex As Exception
'handle this
End Try
End Sub
Public Shared Sub WriteEventToMemory(eventLevel As EventLevel, eventDescription As String, Optional eventSource As String = "")
Dim evt As New AppEvent
evt.Description = eventDescription
evt.Level = eventLevel
evt.EventTime = Now
evt.Source = eventSource
Try
My.Application.AppEvents.Add(evt)
Catch ex As Exception
Throw
End Try
End Sub
Public Shared Sub FlushEventsToLogFile()
WriteEventsToAppLog(My.Application.AppEvents)
End Sub
End Class
There's a few methods in here, but the method called in every exception handler is WriteEventToMemory (it merely adds an AppEvent to the AppEvents list).
An example test routine/worker process (to the local database) looks like:
#Region "local db test"
Private Sub TestLocalDBWorkerProcess_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles TestLocalDBWorkerProcess.DoWork
Me.TestLocalDBStatusMessage = TestLocalDB()
End Sub
Private Sub TestLocalDBWorkerProcess_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles TestLocalDBWorkerProcess.RunWorkerCompleted
Me.prgLocalDatabase.Style = ProgressBarStyle.Blocks
Me.prgLocalDatabase.Value = 100
If Me.ForcedCancelTestLocalDB Then
Me.lbStatus.Items.Add("Local DB Test Cancelled.")
Else
If TestLocalDBStatusMessage.Length > 0 Then
Me.lblLocalDatabaseStatus.Text = "Fail"
Me.lbStatus.Items.Add(TestLocalDBStatusMessage)
SendMessage(Me.prgLocalDatabase.Handle, 1040, 2, 0) 'changes color to red
Else
Me.lblLocalDatabaseStatus.Text = "OK"
Me.lbStatus.Items.Add("Connection to local database is good.")
Me.prgLocalDatabase.ForeColor = Color.Green
End If
End If
Me.ForcedCancelTestLocalDB = False
Me.TestLocalDBProcessing = False
ProcessesFinished()
End Sub
Private Sub StartTestLocalDB()
Me.prgLocalDatabase.Value = 0
Me.prgLocalDatabase.ForeColor = Color.FromKnownColor(KnownColor.Highlight)
Me.prgLocalDatabase.Style = ProgressBarStyle.Marquee
Me.TestLocalDBProcessing = True
Me.TestLocalDBStatusMessage = String.Empty
Me.lblLocalDatabaseStatus.Text = String.Empty
TestLocalDBWorkerProcess = New System.ComponentModel.BackgroundWorker
With TestLocalDBWorkerProcess
.WorkerReportsProgress = True
.WorkerSupportsCancellation = True
.RunWorkerAsync()
End With
End Sub
Private Function TestLocalDB() As String
Dim Statusmessage As String = String.Empty
Try
If Me.TestLocalDBWorkerProcess.CancellationPending Then
Exit Try
End If
If Not QBData.DB.TestConnection(My.Settings.DBConnStr3) Then
Throw New Exception("Unable to connect to local database!")
End If
Catch ex As Exception
Statusmessage = ex.Message
AppLogging.WriteEventToMemory(EventLevel.Fatal, ex.Message, "TestLocalDB")
End Try
Return Statusmessage
End Function
#End Region
The try-catch block simply catches the exception and writes it to memory (I just wrapped it in the WriteEventToMemory method, but it's just adding it to the AppEvents list: My.Application.AppEvents.Add(evt)
Everything appeared to be working peachy, until I noticed that the count for AppEvents was (1) after the Startup event, then it's count was (0) from any of the child processes, finally, the count was (1) when the list was dumped to the error log file (only the first event added was there). It is clearly acting like there are multiple versions of the AppEvents variable.
****** Application Log ******
Logged On: 10/7/2016 6:01:45 PM | Level: Information | Details: Program Started | Source: QBI
Only the first event shows up, the other events not (they are added, there's no null ref exceptions or any exceptions - like phantoms). Any event added to the global variable on the MAIN thread stays (and gets logged, ultimately). So this is clearly a multithreaded issue (never tried this before in a Windows app).
Any ideas on how to remedy?

Answer 1

As mentioned above, I had to pass the events back to the calling workerprocess, so, in the main form I put in:
Private AppEvent_TestLocalDB As New AppEvent
In the DoWork (for each process), I changed it to:
Private Sub TestLocalDBWorkerProcess_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles TestLocalDBWorkerProcess.DoWork
Me.TestLocalDBStatusMessage = TestLocalDB(AppEvent_TestLocalDB)
End Sub
The TestLocalDB sub now looks like:
Private Function TestLocalDB(ByRef aEvent As AppEvent) As String
Dim Statusmessage As String = String.Empty
Try
If Me.TestLocalDBWorkerProcess.CancellationPending Then
Exit Try
End If
If Not QBData.DB.TestConnection(My.Settings.DBConnStr3) Then
Throw New Exception("Unable to connect to local database!")
End If
Catch ex As Exception
Statusmessage = ex.Message
With aEvent
.Description = ex.Message
.Level = EventLevel.Fatal
.Source = "TestLocalDB"
End With
End Try
Return Statusmessage
End Function
Note there is no error logging, just the event variable (ByRef to pass it back, the equivalent to C# out).
When the worker process completes, I add the following:
With AppEvent_TestLocalDB
AppLogging.WriteEventToMemory(.Level, .Description, .Source)
End With
(the other worker processes work the same way)
When ALL the processes are complete, then I flush it to the log file.
AppLogging.FlushEventsToLogFile()
Now the custom event/error log entries look like so (with a freshly made file):
****** Application Log ******
Logged On: 10/7/2016 10:14:36 PM | Level: Information | Details: Program Started | Source: QBI
Logged On: 10/7/2016 10:14:53 PM | Level: Fatal | Details: Unable to connect to local database! | Source: TestLocalDB
That was it - just pass the variable back to the caller