为什么会阻塞？ （带有事件和委托的 VB.NET 多线程）

Question

我有一个功能，DLL 中的类会显示一个表单，要求用户在单击“重试”按钮之前清除打印机上的故障。用户只是点击重试而没有费心清除故障，所以我现在正在编写一个联锁： 调用表单上的按钮将被禁用，直到调用表单上的“启用”方法为止。

这是通过委托调用完成的，因为触发这些更改的事件来自在不同线程上运行的其他 dll。

表单的“enable”方法被连接到一个事件处理程序，处理来自不同线程（监视以太网 IO 服务器的线程）的事件。

我遇到的问题是“_Fault_StateChanged”事件永远不会触发。我怀疑原因是我在这里使用的“ShowDialog”和“DialogResult”技术，但我在该应用程序的其他地方使用了完全相同的技术。

任何建议都会很棒

请参阅下面的代码摘录：

MAIN CLASS 摘录

Public Class StatePrintHandler

    Private WithEvents _RetryForm As frmRetryReject

    Private Delegate Sub delShowRetryDialog()
    Private Delegate Sub delResetEnable()

    Private Sub InvokeResetEnable()
        Dim del As delResetEnable
        del = New delResetEnable(AddressOf ResetEnable)
        del.Invoke()
    End Sub

    Private Sub InvokeRetryDialogue()
        Dim del As delShowRetryDialog
        del = New delShowRetryDialog(AddressOf ShowRetryDialog)
        del.Invoke()
    End Sub

    Private Sub ShowRetryDialog()
        _RetryForm = New frmRetryReject
        _RetryForm.Prep()
        _RetryForm.ShowDialog()
        If (_RetryForm.DialogResult = Windows.Forms.DialogResult.OK) Then
            Me._RetryForm.Visible = False
        End If
    End Sub


Private Sub ResetEnable()
    If (Not IsNothing(_RetryForm)) Then
        _RetryForm.ResetEnable()
    Else
        AuditTrail("Retry form not active, no action", True)
    End If
End Sub


'Event handler for status change coming in on a different thread
    Private Sub _Fault_StateChanged(ByVal sender As Object, ByVal e As Drivers.Common.DigitalSignalChangedEventArgs) Handles _fault.StateChanged
        If (e.NewState) Then
                AuditTrail("Labeller has faulted out during cycling", True)
        Else
                InvokeResetEnable()
        End If
    End Sub
End Class

RETRY FORM CLASS 摘录

Public Class frmRetryReject
    Private Delegate Sub delEnable()
    Public Event Complete()
    Public Sub Prep()
        Me.OK_Button.Enabled = False
    End Sub
    Private Sub OK_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK_Button.Click
        Me.DialogResult = System.Windows.Forms.DialogResult.OK
        Me.Close()
    End Sub
    Public Sub ResetEnable()
        If (IsHandleCreated) Then
            Dim params() As Object = {}
            Me.Invoke(New delEnable(AddressOf InvokeEnable), params)
        End If
    End Sub
    Private Sub InvokeEnable()
        Me.OK_Button.Enabled = True
    End Sub
End Class

针对 Daniel 的评论的其他详细信息

此处的代码不完整，它是摘录。故障对象是对外部库的订阅，并且是以太网 IO 服务器的处理程序。 当 IOServer 上的数字输入发生更改时，会触发 _fault StateChanged 事件。我知道以下几点： 我的跟踪文件显示信号变高，这会调用重试形式。 当重试屏幕仍然显示时，信号物理再次变为低电平。 ...但是事件不会触发

这就像应用程序无法为传入的事件提供服务，直到 ShowDialog/DialogResult 完成 - 但我对此感到困惑，因为我知道 .NET 2.0 中的 ShowDialog 没有阻止，我仍然应该能够为事件提供服务，并且在应用程序的其他地方使用了相同的模式。

有几点需要注意： MAIN CLASS 在运行时通过基于配置的反射动态实例化。 这是 VS2005 SP2

如果这有帮助的话，我会将整个类发布在另一个代码框中，但它可能会使场景拥挤......

谢谢 安迪

Imports System.IO
Imports ACS.Interfaces
Imports ACS.Pallet

Public Class StateCimPAKPrintHandler
    Inherits StateBase
    Private WithEvents _ioManager As ACS.Components.DigitalIOManager
    Private _config As StateCimPAKPrintHandlerBootstrap
    Private CONST_OutcomeOK As String = "OK"
    Private CONST_OutcomeRetry As String = "Retry"
    Private CONST_OutcomeException As String = "Exception"

    Private WithEvents _busy As ACS.Drivers.Common.InputSignal
    Private WithEvents _fault As ACS.Drivers.Common.InputSignal
    Private WithEvents _print As ACS.Drivers.Common.OutputSignal
    Private WithEvents _palletRelease As ACS.Drivers.Common.OutputSignal

    Private _labellingInProgress As Boolean
    Private _faulted As Boolean
    Private _retryScreenInvoked As Boolean
    Private WithEvents _timeout As System.Timers.Timer
    Private WithEvents _faultTimer As System.Timers.Timer

    Private WithEvents _RetryForm As frmRetryReject

    Private Delegate Sub delShowRetryDialog()
    Private Delegate Sub delResetEnable()

    Private Sub InvokeResetEnable()
        Dim del As delResetEnable
        del = New delResetEnable(AddressOf ResetEnable)
        del.Invoke()
    End Sub

    Private Sub InvokeRetryDialogue()
        Dim del As delShowRetryDialog
        del = New delShowRetryDialog(AddressOf ShowRetryDialog)
        del.Invoke()
    End Sub

    Private Sub ShowRetryDialog()
        _timeout.Stop()
        _retryScreenInvoked = True
        _RetryForm = New frmRetryReject
        _RetryForm.Prep()
        AuditTrail("Displaying Retry screen", True)
        _RetryForm.ShowDialog()
        If (_RetryForm.DialogResult = Windows.Forms.DialogResult.OK) Then
            AuditTrail("User clicked RETRY LINE on the RETRY dialogue", True)
            _retryScreenInvoked = False
            Me._RetryForm.Visible = False
            Me.SetOutcome(CONST_OutcomeRetry)
        End If
    End Sub

    Private Sub ResetEnable()
        If (Not IsNothing(_RetryForm)) Then
            _RetryForm.ResetEnable()
        Else
            AuditTrail("Retry form not active, no action", True)
        End If
    End Sub

    Public Sub New(ByVal Sequencer As ISequencer, ByVal ParentPlt As ACS.Interfaces.IPallet, ByVal Name As String)
        MyBase.New(Sequencer, ParentPlt, Name)
        _timeout = New System.Timers.Timer
        _faultTimer = New System.Timers.Timer
        _config = New StateCimPAKPrintHandlerBootstrap(Me._myIniFileName, Name)
        _timeout.Interval = _config.CycleTimeoutMS
        _faultTimer.Interval = 750
        _retryScreenInvoked = False
        _RetryForm = New frmRetryReject
        Me._RetryForm.Visible = False
        _ioManager = ACS.Components.DigitalIOManager.GetInstance
        _busy = _ioManager.GetInput("Busy")
        _fault = _ioManager.GetInput("CimPAKFault")
        _print = _ioManager.GetOutput("Print")
        _palletRelease = _ioManager.GetOutput("PalletRelease")
    End Sub
    Public Overrides Sub Kill()
        _ioManager = Nothing
        _RetryForm = Nothing
        _busy = Nothing
        _fault = Nothing
        _print = Nothing
        _timeout = Nothing
        _faultTimer = Nothing
        _pallet = Nothing
    End Sub
    Public Overrides Sub Execute()
        AuditTrail("Pulsing Print Signal", True)
        _print.PulseOutput(3000)
        _labellingInProgress = True
        _timeout.Start()
    End Sub
    Private Sub _busy_StateChanged(ByVal sender As Object, ByVal e As Drivers.Common.DigitalSignalChangedEventArgs) Handles _busy.StateChanged
        _timeout.Stop()
        AuditTrail("Busy signal changed to : " & e.NewState, True)
        If (e.NewState) Then
            _faulted = False
            AuditTrail("CimPAK = Busy High", True)
            _labellingInProgress = True
        Else
            AuditTrail("CimPAK = Busy Low", True)
            AuditTrail("Wait 750 milliseconds for any faults", True)
            _faultTimer.Start()
        End If
    End Sub
    Private Sub _Fault_StateChanged(ByVal sender As Object, ByVal e As Drivers.Common.DigitalSignalChangedEventArgs) Handles _fault.StateChanged
        AuditTrail("Fault signal changed to : " & e.NewState, True)
        If (e.NewState) Then
            If (_labellingInProgress = True) Then
                AuditTrail("Labeller has faulted out during cycling", True)
                _faulted = True
                If (Not _retryScreenInvoked) Then
                    InvokeRetryDialogue()
                End If
            Else
                AuditTrail("Labeller has faulted out between cycles, no action can be taken", True)
            End If
        Else
            If (_retryScreenInvoked) Then
                AuditTrail("Enable button on Retry screen", True)
                InvokeResetEnable()
            End If
            _faulted = False
        End If
    End Sub
    Private Sub _faultTimer_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles _faultTimer.Elapsed
        _faultTimer.Stop()
        If (_faulted) Then
            AuditTrail("System has faulted", True)
        Else
            AuditTrail("No fault occured, assume pallet is OK to release", True)
            AuditTrail("CimPAK cycle complete", True)
            _labellingInProgress = False
            _palletRelease.PulseOutput(3000)
            Me.SetOutcome(CONST_OutcomeOK)
        End If
    End Sub
    Private Sub _timeout_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles _timeout.Elapsed
        _timeout.Stop()
        AuditTrail("Labeller print cycle timed out", True)
        If (Not _retryScreenInvoked) Then
            _retryScreenInvoked = True
            InvokeRetryDialogue()
            InvokeResetEnable()
        End If
    End Sub



End Class

#Region "Bootstrap"
Public Class StateCimPAKPrintHandlerBootstrap
    Private Const CONST_CycleTimeoutMS As String = "CycleTimeoutMS"
    Private _CycleTimeoutMS As Long
#Region "Properties"
    Public ReadOnly Property CycleTimeoutMS() As Long
        Get
            Return _CycleTimeoutMS
        End Get
    End Property
#End Region
    Public Sub New(ByVal IniFile As String, ByVal Name As String)
        Try
            Dim _cfgFile As String = Environ("ACSVAR") & "\" & IniFile
            ' Check to see if the CFG file exits
            If File.Exists(_cfgFile) = False Then
                Throw New Exception("Configuration file does not exist: " & _cfgFile)
            Else
                'Get values
                _CycleTimeoutMS = ACS.Utility.Configuration.GetLong(_cfgFile, Name, CONST_CycleTimeoutMS)
            End If
        Catch ex As Exception
            Throw
        End Try
    End Sub
End Class
#End Region

Answer 1

尝试查看

Visual Basic，子线程阻塞主线程

多线程示例中的答案和

新线程仍然阻塞 UI -Thread

来自（我）对于模型线程的回答......这两个应该给你编写的代码来启动。

Answer 2

我已经很长时间没有做过任何 Winforms 工作了，但是您是否以模式方式显示对话框？因为这可能是委托调用未到达的原因。

异步委托的工作方式是将调用详细信息序列化到框架内部的内存位置，然后将窗口消息发布到相关线程的顶级窗口。模态对话框的工作方式是进入消息处理循环，该循环窃取线程的所有消息，以便只有一个对话框可以响应。您可以看到这可能会发生冲突。