Possible threading issue.

[texasdru92]

I noticed that some of my conveyors/diverts weren't updating properly, so I added some debug statements to investigate. I discovered that my bool variables were being set to True, but before the method finished executing, the variables were changing back to False—even though the actual PLC bit being monitored remained True the entire time. I suspect this was a threading issue, and adding a synclock seems to have resolved it. I'm using DataSubscriber2 and basicindicators to show the status of the conveyors. Has anyone else encountered a similar issue?

Code: [Select]

    Private Sub UpdateConveyorStatus(
    e As Drivers.Common.PlcComEventArgs,
    ByRef conveyorStatus As ConveyorStatus,
    plcActive As String,
    plcHalfFull As String,
    plcFull As String,
    plcJam As String,
    plcMotorFault As String,
    plcEstop As String,
    plcInterlock As String
)
        SyncLock lockObject
            ' Update the state properties based on PLC address
            If e.PlcAddress = plcFull Then
                conveyorStatus.Full = e.Values(0) = True
            End If

            If e.PlcAddress = plcActive Then
                Debug.WriteLine($"[DEBUG] PLC Address: {e.PlcAddress}, Received Value: {e.Values(0)}, Time: {DateTime.Now}")
                If conveyorStatus.Active <> (e.Values(0) = True) Then
                    conveyorStatus.Active = e.Values(0) = True
                    Debug.WriteLine($"[DEBUG] Active state updated to: {conveyorStatus.Active}")
                Else
                    Debug.WriteLine("[DEBUG] No change in Active state.")
                End If
            End If

            If e.PlcAddress = plcHalfFull Then
                conveyorStatus.HalfFull = e.Values(0) = True
            End If

            If e.PlcAddress = plcJam Then
                conveyorStatus.Jam = e.Values(0) = True
            End If

            If e.PlcAddress = plcMotorFault Then
                conveyorStatus.MotorFault = e.Values(0) = True
            End If

            If e.PlcAddress = plcEstop Then
                conveyorStatus.Estop = e.Values(0) = True
            End If

            If e.PlcAddress = plcInterlock Then
                conveyorStatus.Interlock = e.Values(0) = True
            End If

            ' Update conveyor color based on the states
            If conveyorStatus.Estop Then
                conveyorStatus.Conveyor.Color1 = Color.Red
            ElseIf conveyorStatus.Interlock Then
                conveyorStatus.Conveyor.Color1 = Color.Orange
            ElseIf conveyorStatus.Jam Then
                conveyorStatus.Conveyor.Color1 = Color.Orange
            ElseIf conveyorStatus.MotorFault Then
                conveyorStatus.Conveyor.Color1 = Color.Red
            ElseIf conveyorStatus.Active And Not conveyorStatus.HalfFull And Not conveyorStatus.Full Then
                conveyorStatus.Conveyor.Color1 = Color.Green
                Debug.WriteLine("[DEBUG] Active green")
            ElseIf conveyorStatus.Active And conveyorStatus.Full And conveyorStatus.HalfFull Then
                conveyorStatus.Conveyor.Color1 = Color.Blue
            ElseIf conveyorStatus.Active And Not conveyorStatus.Full And conveyorStatus.HalfFull Then
                conveyorStatus.Conveyor.Color1 = Color.Yellow
            ElseIf Not conveyorStatus.Active Then
                conveyorStatus.Conveyor.Color1 = Color.DarkGray
                Debug.WriteLine($"Active = {conveyorStatus.Active}")
                Debug.WriteLine("[DEBUG] Inactive gray")
            Else
                conveyorStatus.Conveyor.Color1 = Color.DarkGray
                Debug.WriteLine("[DEBUG] Fallback gray")
            End If
        End SyncLock
    End Sub



[Archie]

I'm not following what you are doing here:

Code: [Select]

conveyorStatus.Full = e.Values(0) = True
It appears you are over-writing the result (e.values(0)) returned from the driver and always making it True no matter what the PLC value has.

[texasdru92]

Having it set up this way actually works. It evaluates the expression e.Values(0) = True and stores the result in conveyorStatus.Full. I've done something similar in other languages, but the difference is that the assignment operator is = in VB.NET, while the equality operator is == in other languages (not = like in VB). My thought process was to evaluate whatever e.Values(0) is and check if it equals True, and if not, return False and assign the result to the variable.

[Archie]

That's interesting, I never seen it done that way. I tested it and it does work.

If you are using a DataSubscriber2, the callback routine should be synchronizing to the UI thread and not allow parallel execution of the callback routine. I would be interested in seeing a breakpoint put in the DataSubscriber2 code in the OnDataReturned routine to see if the m_SynchronizationContext is set to anything:

Code: [Select]

    Protected Overridable Sub OnDataReturned(ByVal e As MfgControl.AdvancedHMI.Drivers.Common.PlcComEventArgs)
        If m_synchronizationContext IsNot Nothing Then
            m_synchronizationContext.Post(AddressOf DataReturnedSync, e)
        Else
            RaiseEvent DataReturned(Me, e)
        End If
    End Sub

    '****************************************************************************
    '* This is required to sync the event back to the parent form's main thread
    '****************************************************************************
    'Dim drsd As EventHandler(Of MfgControl.AdvancedHMI.Drivers.Common.PlcComEventArgs) = AddressOf DataReturnedSync
    Private Sub DataReturnedSync(ByVal e As Object)
        RaiseEvent DataReturned(Me, DirectCast(e, MfgControl.AdvancedHMI.Drivers.Common.PlcComEventArgs))
    End Sub


[texasdru92]

I got my code to work. I converted my class, which is not in the code I shared, and made it into one simple function instead. I think my issue was the way I was trying to use my class. Here is my updated code that works:

Code: [Select]

    Private Sub UpdateConveyorStatus(
    e As Drivers.Common.PlcComEventArgs,
    ByRef conveyorStatus As AdvancedHMIControls.BasicIndicator,
    ByRef Active As Boolean,
    ByRef HalfFull As Boolean,
    ByRef Full As Boolean,
    ByRef Jam As Boolean,
    ByRef MotorFault As Boolean,
    ByRef Estop As Boolean,
    ByRef Interlock As Boolean,
    ByRef plcActive As String,
    ByRef plcHalfFull As String,
    ByRef plcFull As String,
    ByRef plcJam As String,
    ByRef plcMotorFault As String,
    ByRef plcEstop As String,
    ByRef plcInterlock As String)

        ' SyncLock lockObject

            Dim currentTime As DateTime = DateTime.Now
            'If (currentTime - lastUpdateTime).TotalMilliseconds < 500 Then
            'Debug.WriteLine("[DEBUG] Ignoring rapid state change.")
            'Exit Sub
            'End If
            lastUpdateTime = currentTime


            ' Update the state properties based on PLC address
            If plcFull IsNot "NA" Then
                If e.PlcAddress = plcFull Then
                    Full = e.Values(0) = True
                End If
            End If

            If plcActive IsNot "NA" Then
                If e.PlcAddress = plcActive Then
                    Debug.WriteLine($"[DEBUG] PLC Address: {e.PlcAddress}, Received Value: {e.Values(0)}, Time: {DateTime.Now}")
                    If e.Values(0) = True Then
                        Active = e.Values(0) = True
                        Debug.WriteLine($"[DEBUG] Active state updated to: {Active}")
                    Else
                        Debug.WriteLine("[DEBUG] No change in Active state.")
                        Active = False
                    End If
                End If
            Else
                Active = False
            End If

            If plcHalfFull IsNot "NA" Then
                If e.PlcAddress = plcHalfFull Then
                    HalfFull = e.Values(0) = True
                End If
            Else
                HalfFull = False
            End If

            If plcJam IsNot "NA" Then
                If e.PlcAddress = plcJam Then
                    Jam = e.Values(0) = True
                End If
            Else
                Jam = False

            End If

            If plcMotorFault IsNot "NA" Then
                If e.PlcAddress = plcMotorFault Then
                    MotorFault = e.Values(0) = True
                End If
            Else
                MotorFault = False
            End If

            If plcEstop IsNot "NA" Then
                If e.PlcAddress = plcEstop Then
                    Estop = e.Values(0) = True
                    Debug.WriteLine($"E-Stop = {Estop}")
                End If
            Else
                Estop = False
                Debug.WriteLine($"E-Stop = {Estop}")
            End If


            If plcInterlock = "NA" Then
                If e.PlcAddress = plcInterlock Then
                    Interlock = e.Values(0) = True
                End If
            Else
                Interlock = False
            End If

            ' Determine the new color based on the states

            If Estop Then
                conveyorStatus.Color1 = Color.Red
            ElseIf Interlock Then
                conveyorStatus.Color1 = Color.Orange
            ElseIf Jam Then
                conveyorStatus.Color1 = Color.Orange
            ElseIf MotorFault Then
                conveyorStatus.Color1 = Color.Red
            ElseIf Active And Not HalfFull And Not Full Then
                conveyorStatus.Color1 = Color.Green
                Debug.WriteLine("[DEBUG] Active green")
            ElseIf Active And Full And HalfFull Then
                conveyorStatus.Color1 = Color.Blue
            ElseIf Active And Not Full And HalfFull Then
                conveyorStatus.Color1 = Color.Yellow
            ElseIf Active = False Then
                conveyorStatus.Color1 = Color.DarkGray
                Debug.WriteLine("[DEBUG] Inactive gray")
            End If
        ' End SyncLock
    End Sub