Multithreading and Event Marshalling Question Using The Tricks Threading example

[smkperu]

Private events won't work, because they require marshaling.

Hello Trick,

Did not understand.

1. Can you show how to make private objects/events work using marshalling using Marshal/Marshal2 and UnMarshal functions along with CreatePrivateObjectByNameInNewThread.

2. Can the above be extended for public objects(activex objects)/events using CreateActiveXObjectInNewThread2.


Thanks

[The trick]

1. Can you show how to make private objects/events work using marshalling using Marshal/Marshal2 and UnMarshal functions along with CreatePrivateObjectByNameInNewThread.

Private objects don't support events because events require marshaling. You can use another solution to notify the main thread (see examples).

2. Can the above be extended for public objects(activex objects)/events using CreateActiveXObjectInNewThread2.

Public events are supported. You can declare variable as usual.

[smkperu]

Hello Trick,

You have already shown how to add private user controls to forms at runtime at

https://www.vbforums.com/showthread....=1#post5447871

by making changes in new thread to support apartment model in CreateVBHeaderCopy at runtime.

In a similar way can we receive events from this user control at runtime with some changes.


Thanks

[The trick]

smkperu i see you don't understand what is marshaling is for. You can't share a COM (STA) object reference without marshaling. When you declare a variable with a private interface there is no information how to transfer the parameters from one apartment to another one. When you declare a variable with a public interface it uses description from a typelibrary. There is no typelibrary for private interfaces/classes in VB.

[smkperu]

smkperu i see you don't understand what is marshaling is for. You can't share a COM (STA) object reference without marshaling. When you declare a variable with a private interface there is no information how to transfer the parameters from one apartment to another one. When you declare a variable with a public interface it uses description from a typelibrary. There is no typelibrary for private interfaces/classes in VB.

Hello Trick,

When we declare a private user object in one thread in standard exe project if we want to call its methods to be called from another thread
we use Marshal/Marshal2 to marshal it to the other thread and we obtain unmarshaled object in new thread using unmarshal.
So when we are using marshalling for private objects manually why not we use marshalling for private user events also manually.Can you show using a simple example for my understanding.

Thanks

[The trick]

Hello Trick,

When we declare a private user object in one thread in standard exe project if we want to call its methods to be called from another thread
we use Marshal/Marshal2 to marshal it to the other thread and we obtain unmarshaled object in new thread using unmarshal.
So when we are using marshalling for private objects manually why not we use marshalling for private user events also manually.Can you show using a simple example for my understanding.

Thanks

We never get an unmarshaled object but we get unmarshaled interface reference (pointer). I never use private interfaces in my examples. If you noted i use Object (or another public interface) type which is public IDispatch interface alias.

[smkperu]

We never get an unmarshaled object but we get unmarshaled interface reference (pointer). I never use private interfaces in my examples. If you noted i use Object (or another public interface) type which is public IDispatch interface alias.

Hello Trick,

I achieved using receiving events in standard exe
using the following code in Form1 :

Public WithEvents m_class1 As Class1
Private Sub Command1_Click()
Dim thid As Long
Set lfrm1 = Me
vbCreateThread 0, 0, AddressOf th1, 0, 0, thid
End Sub



Private Sub Form_Load()
modMultiThreading.Initialize
Me.Caption = App.ThreadID
End Sub

Private Sub Form_Unload(Cancel As Integer)
modMultiThreading.Uninitialize
End Sub

Private Sub m_class1_abc()

MsgBox "in abc evt threadid= " & App.ThreadID

End Sub


where th1 is defined in modMultiThreading2 as follows:


' // Private object thread
Public Function th1( _
                 ByVal data As Long) As Long
Dim lclass1 As Object

Set lclass1 = New Class1
Set lfrm1.m_class1 = lclass1
lclass1.memfunc
End Function

I defined lfrm1 As global in module as follows:


Public lfrm1 As Object

and initialized in Command_Click() as follows:

Set lfrm1 = Me

and used it to get m_class1 in thread th1 as follows:

Set lfrm1.m_class1 = lclass1

Is this the correct way or is there any other method
of getting main thread form1 object.


Thanks

[The trick]

It isn't correct because you access to the lfrm1 from another thread without marshaling.

[smkperu]

It isn't correct because you access to the lfrm1 from another thread without marshaling.

Hello Trick,

As you already said for Private objects I will use notification solution to the main thread instead of events.

But for public objects how can we receive events from arbitrary threads like calling callbacks from arbitrary threads

using InitCurrentThreadAndCallFunction of modMultThreading2.bas like in Callback demo.


Thanks

[The trick]

Hello Trick,

As you already said for Private objects I will use notification solution to the main thread instead of events.

But for public objects how can we receive events from arbitrary threads like calling callbacks from arbitrary threads

using InitCurrentThreadAndCallFunction of modMultThreading2.bas like in Callback demo.


Thanks

By using WithEvents statement.

[smkperu]

By using WithEvents statement.

Hello Trick,

Events are received in the same thread in which the source object is called which always requires extra thread on the client side so as to keep the main thread always responsive.
But this not the case with callbacks where this extra thread is not required since callbacks from arbitrary threads of component run directly in client independent of main thread.
How to overcome this overhead of extra thread when using events on client side using
withevents.

Thanks

[The trick]

Hello Trick,

Events are received in the same thread in which the source object is called which always requires extra thread on the client side so as to keep the main thread always responsive.
But this not the case with callbacks where this extra thread is not required since callbacks from arbitrary threads of component run directly in client independent of main thread.
How to overcome this overhead of extra thread when using events on client side using
withevents.

Thanks

Read about marshaling. When a COM object fires an event it transmits the call to all the apartments subscribed.

[smkperu]

Read about marshaling. When a COM object fires an event it transmits the call to all the apartments subscribed.

Hello Trick,

Visual Basic uses apartment threading model. Cross-thread function calls need
to be marshalled. Visual Basic does not support events fired directly from any
thread other than the main thread created by a Visual Basic project without
marshalling.

In order Fire Event in Secondary thread we have to
Marshal the event firing code:

1. The thread being spun off needs to call CoInitialize/CoUnInitialize.

2. The sink interface being called back on in the thread must be marshalled over
to that thread with CoMarshalInterThreadInterfaceInStream/CoGetInterfaceAndReleaseStream.

This shows that even though the event is fired in Secondary thread of public object
or component thru sink interface it is received in the same thread from which the source object was called at the client side.

But this is not the case with callbacks and the callback is called in new thread directly because no marshalling is required.

Thanks

[The trick]

Hello Trick,

Visual Basic uses apartment threading model. Cross-thread function calls need
to be marshalled. Visual Basic does not support events fired directly from any
thread other than the main thread created by a Visual Basic project without
marshalling.

In order Fire Event in Secondary thread we have to
Marshal the event firing code:

1. The thread being spun off needs to call CoInitialize/CoUnInitialize.

2. The sink interface being called back on in the thread must be marshalled over
to that thread with CoMarshalInterThreadInterfaceInStream/CoGetInterfaceAndReleaseStream.

This shows that even though the event is fired in Secondary thread of public object
or component thru sink interface it is received in the same thread from which the source object was called at the client side.

But this is not the case with callbacks and the callback is called in new thread directly because no marshalling is required.

Thanks

This is the COM rules. If you need to use raw callbacks you should use InitCurrentThreadAndCallFunction.

[smkperu]

This is the COM rules. If you need to use raw callbacks you should use InitCurrentThreadAndCallFunction.

Hello Trick,

I mentioned about the same raw callbacks as callbacks in the callback demo provided.
How to fire event from a secondary thread using sink interface so that it can behave just like
this raw callbacks ie., the event should be able to be received in the same secondary thread.


Thanks

[The trick]

Hello Trick,

I mentioned about the same raw callbacks as callbacks in the callback demo provided.
How to fire event from a secondary thread using sink interface so that it can behave just like
this raw callbacks ie., the event should be able to be received in the same secondary thread.


Thanks

COM events should follow COM rules. VB thread is STA thread so it can only process the events in the subscriber STA.

[smkperu]

COM events should follow COM rules. VB thread is STA thread so it can only process the events in the subscriber STA.

Hello Trick,

This is the reason I mentioned that we have to create another(extra) VB thread on client side so that events can be processed or received in this subscriber thread without disturbing
the default main VB thread.

Thanks

[smkperu]

Hello Trick,

If I use a public object in (activex dll) with atleast one event and use it in my standard exe supporting MultiThreading( using your modMultiThreading2.bas) by adding thru project references,
what is the difference I get when the activex dll is having Threading model set to
1.single threaded
2.apartment threaded.

Can you provide a simple example.

Thanks

[The trick]

Hello Trick,

If I use a public object in (activex dll) with atleast one event and use it in my standard exe supporting MultiThreading( using your modMultiThreading2.bas) by adding thru project references,
what is the difference I get when the activex dll is having Threading model set to
1.single threaded
2.apartment threaded.

Can you provide a simple example.

Thanks

1 - all the instances should live in the main STA thread;
2 - all the instances can live in the different STA threads.

[smkperu]

1 - all the instances should live in the main STA thread;
2 - all the instances can live in the different STA threads.

Hello Trick,

Can you show this instances with simple example.

Thanks

[smkperu]

Hello Trick,

1. In a std exe

when we create and display a private object in new thread it is created in new thread.

But even when we create and display a public object in new thread it is created in main thread which can be verified by displaying app.ThreadId if the public object threading model is single threaded.

Why is this difference between a private object in a standard exe and public object(single threaded) used in the same standard exe even though we are displaying in new thread using vbCreateThread.
What is the threading model of standard exe for this private object .Projects (public object and std exe) attached.

2. In a activex dll with single threaded

when we create a new thread and display a std exe private object it is displayed in new thread successfully.


But in a activex dll with apartment threaded
when we create a new thread and display a std exe private object it fails.How to make the private object creation successful.

Thanks

[The trick]

If an ActiveX DLL has the single threading model it works as it should (because it's the COM rules). If each object in single thread model will live in its own thread it won't work because library doesn't expect such behavior (for example there is no global variable isolation).

[smkperu]

If an ActiveX DLL has the single threading model it works as it should (because it's the COM rules). If each object in single thread model will live in its own thread it won't work because library doesn't expect such behavior (for example there is no global variable isolation).

Hello Trick,

When we create a thread in std exe it works when we use vbCreateThread without any restrictions.

But when we create thread in public object actx dll(single threaded) and try to run it in std exe
it crashes. How to make this to work successfully without crash in the actx dll(single threaded) just like vbCreateThread in std exe.

Projects(stdexe and actx dll(single threaded)) simpleactsingledemo attached

Thanks

[The trick]

I don't understand you and didn't see my module in your project.

[smkperu]

I don't understand you and didn't see my module in your project.

Hello Trick,

This is similar to your callback demo.
Only difference is you are using standard dll(CallbackDll.dll) and I am using (activex dll single threaded)simpleactsingle.dll.

You are using CreateThread api in CallbackDll project as I do in simpleactsingle.dll.

But here there is a difference.I am trying to use my activex dll private objects or MsgBox for example to be shown in thread using thread initialization thru multi use class object creation using CreateObject in the thread in dll.

You have not created any private objects like forms or MsgBox in new thread of CallbackDll standard dll project.You are only showing how to use resources of standard exe thru its callback in the thread to which CallbackDll.dll is loaded.

Now coming to (activex dll singlethreaded)simpleactsingle.dll.If I set the project to apartment threaded
and run the std exe I get my form or msgbox of actx dll displayed in thread without having to use vbCreateThread or your module successfully without crash.


But since the same simpleactsingle.dll is crashing when set to single threaded I was asking can I avoid this crash and make the demo run successfully by using module(vbheader solution in exe or dll) in the project so that I can show MsgBox or private objects of my activex dll (single threaded) in the dll thread thru std exe.


Thanks

[xiaoyao]

What is a multithreaded solution that can run stably under the VB6 IDE without crashing? No need to debug, just run once, stop, then F5, repeat many times running without crashing.

[The trick]

What is a multithreaded solution that can run stably under the VB6 IDE without crashing? No need to debug, just run once, stop, then F5, repeat many times running without crashing.

This module runs the code in the main thread when you debug in IDE.

[smkperu]

This module runs the code in the main thread when you debug in IDE.

Hello Trick,

When we run the code with actx dll set to single threaded the code in the dll thread runs in main thread even when run compiled outside IDE according to COM rules as you already explained.
The code in the Dll thread runs in the same new thread when set to Apartment threaded model when run compiled.

There are two options:

Either

1. Change the threading model to Apartment Threaded dynamically at runtime before starting the thread so that it runs as Apartenet threaded and after thread completion reset it to single threaded.

or

2. initialize the Dll thread properly either thru vbheader or creating multiuse class so that the code in the thread runs in main thread without crashing when the dll thread is set to single threaded model.

How can the above two tasks achieved.

Thanks

[xiaoyao]

Would it be better to use multiple processes to simulate multiple threads?

[Cube8]

Would it be better to use multiple processes to simulate multiple threads?

You can have multiple processes, but this topic is about having a single exe.

[xiaoyao]

You can have multiple processes, but this topic is about having a single exe.

I mean there is no way to debug multithreading in the VB6 IDE.If we open three VB6 processes to simulate multithreading and then debug. It's more fun this way. One of them is used as the main process UI to display the running progress.

[xiaoyao]

You need to write a plug-in that starts three processes at the same time, and can also pause or end at the same time.

[xiaoyao]

Has anyone learned how to debug VB6 multithreading? If you open a main program, three child processes. () Write a plug-in addin, a total of 4 VB6 processes, can turn three child processes into tabs, can run at the same time pause the end.

In fact, it is good to copy the project into multiple projects and open them at the same time when needed.The main technical difficulty is the common variable.

[smkperu]

Hello Trick,

When we create a thread in std exe it works when we use vbCreateThread without any restrictions.

But when we create thread in public object actx dll(single threaded) and try to run it in std exe
it crashes. How to make this to work successfully without crash in the actx dll(single threaded) just like vbCreateThread in std exe.

Projects(stdexe and actx dll(single threaded)) simpleactsingledemo attached

Thanks

Hello Trick,

I made a activex dll (single threaded) actxdllwithapt_threaded1.dll with a form, module and multiuse class as follows:

Class1 (multiuse class) code

Option Explicit

Dim lThreadId   As Long
Dim hThread     As Long



Public Sub CreateFormofdllinNewThread()
    
    Dim tThData  As tThreadData
    
    hThread = CreateThread(ByVal 0&, 0, AddressOf ThreadProc, tThData, 0, lThreadId)
       
End Sub


Public Sub CloseThread()
    
    If lThreadId = 0 Then Exit Sub
    
 
    CloseHandle hThread
    lThreadId = 0
    
End Sub

Private Sub Class_Terminate()
    CloseThread
End Sub

modMain.bas module code

Option Explicit
Public Const PAGE_EXECUTE_READWRITE         As Long = &H40&
Public Const CC_STDCALL     As Long = 4
Public Const WM_EXITTHREAD  As Long = &H8001&

' // Lazy GUID structure
Public Type tCurGUID
    c1          As Currency
    c2          As Currency
End Type

Public Type tThreadData
    pStream     As Long
    hEvent      As Long
End Type

Public Type POINTAPI
    x                   As Long
    y                   As Long
End Type

Public Type MSG
    hwnd                As Long
    message             As Long
    wParam              As Long
    lParam              As Long
    time                As Long
    pt                  As POINTAPI
End Type


''''''''''''''''''''''''''''''''''''''''''

'Option Explicit

'Private Const CC_STDCALL As Long = 4


Private Declare Function LoadLibrary Lib "kernel32" _
                         Alias "LoadLibraryW" ( _
                         ByVal lpLibFileName As Long) As Long
Private Declare Function GetProcAddress Lib "kernel32" ( _
                         ByVal hModule As Long, _
                         ByVal lpProcName As String) As Long
Private Declare Function FreeLibrary Lib "kernel32" ( _
                         ByVal hLibModule As Long) As Long
Private Declare Function GetMem4 Lib "msvbvm60" ( _
                         ByRef pSrc As Any, _
                         ByRef pDst As Any) As Long
Private Declare Function lstrcmpA Lib "kernel32" ( _
                         ByRef lpString1 As Any, _
                         ByRef lpString2 As Any) As Long
Private Declare Function memcpy Lib "kernel32" _
                         Alias "RtlMoveMemory" ( _
                         ByRef Destination As Any, _
                         ByRef Source As Any, _
                         ByVal Length As Long) As Long

                         
Private m_cFactory  As IUnknown
Private m_cContext  As Object
Private m_hLibrary  As Long


''''''''''''''''''''''''''''''''''''''''''

Public Declare Function GetModuleHandle Lib "kernel32" _
                         Alias "GetModuleHandleW" ( _
                         ByVal lpModuleName As Long) As Long



Public Declare Function CreateIExprSrvObj Lib "MSVBVM60.DLL" ( _
                        ByVal pUnk1 As Long, _
                        ByVal lUnk2 As Long, _
                        ByVal pUnk3 As Long) As IUnknown

Public Declare Function PostThreadMessage Lib "user32" _
                        Alias "PostThreadMessageW" ( _
                        ByVal idThread As Long, _
                        ByVal uMsg As Long, _
                        ByVal wParam As Long, _
                        ByVal lParam As Long) As Long
Public Declare Function PostQuitMessage Lib "user32" ( _
                        ByVal nExitCode As Long) As Long
Public Declare Function GetMessage Lib "user32" _
                        Alias "GetMessageW" ( _
                        ByRef lpMsg As Any, _
                        ByVal hwnd As Long, _
                        ByVal wMsgFilterMin As Long, _
                        ByVal wMsgFilterMax As Long) As Long
Public Declare Function TranslateMessage Lib "user32" ( _
                        ByRef lpMsg As Any) As Long
Public Declare Function DispatchMessage Lib "user32" _
                        Alias "DispatchMessageW" ( _
                        ByRef lpMsg As Any) As Long
Public Declare Function CoInitialize Lib "ole32" ( _
                        ByRef pvReserved As Any) As Long
Public Declare Function CreateThread Lib "kernel32" ( _
                        ByRef lpThreadAttributes As Any, _
                        ByVal dwStackSize As Long, _
                        ByVal lpStartAddress As Long, _
                        ByRef lpParameter As Any, _
                        ByVal dwCreationFlags As Long, _
                        ByRef lpThreadId As Long) As Long
Public Declare Function CoMarshalInterThreadInterfaceInStream Lib "ole32.dll" ( _
                        ByRef riid As Any, _
                        ByVal pUnk As Any, _
                        ByRef ppstm As Any) As Long
Public Declare Function CoGetInterfaceAndReleaseStream Lib "ole32.dll" ( _
                        ByVal pstm As Long, _
                        ByRef riid As Any, _
                        ByRef pUnk As Any) As Long
Public Declare Function CreateStreamOnHGlobal Lib "ole32" ( _
                        ByVal hGlobal As Long, _
                        ByVal fDeleteOnRelease As Long, _
                        ByRef ppstm As Any) As Long
Public Declare Function CloseHandle Lib "kernel32" ( _
                        ByVal hObject As Long) As Long
Public Declare Function WaitForSingleObject Lib "kernel32" ( _
                        ByVal hHandle As Long, _
                        ByVal dwMilliseconds As Long) As Long
Public Declare Function CreateEvent Lib "kernel32" _
                        Alias "CreateEventW" ( _
                        ByRef lpEventAttributes As Any, _
                        ByVal bManualReset As Long, _
                        ByVal bInitialState As Long, _
                        ByVal lpName As Long) As Long
Public Declare Function SetEvent Lib "kernel32" ( _
                        ByVal hEvent As Long) As Long
Public Declare Function DestroyWindow Lib "user32" ( _
                        ByVal hwnd As Long) As Long
                        
                        
Public Declare Sub CoUninitialize Lib "ole32" ()
Public Declare Function DispCallFunc Lib "oleaut32.dll" ( _
                        ByRef pvInstance As Any, _
                        ByVal oVft As Long, _
                        ByVal cc As Long, _
                        ByVal vtReturn As VbVarType, _
                        ByVal cActuals As Long, _
                        ByRef prgvt As Any, _
                        ByRef prgpvarg As Any, _
                        ByRef pvargResult As Variant) As Long

Public Declare Function MessageBox Lib "user32" Alias "MessageBoxA" (ByVal hwnd As Long, ByVal lpText As String, ByVal lpCaption As String, ByVal wType As Long) As Long
Public Declare Function VirtualProtect Lib "kernel32" ( _
                         ByVal lpAddress As Long, _
                         ByVal dwSize As Long, _
                         ByVal flNewProtect As Long, _
                         ByRef lpflOldProtect As Long) As Long
Public Declare Function VBDllGetClassObject Lib "MSVBVM60.DLL" ( _
                         ByRef phModule As Long, _
                         ByVal lReserved As Long, _
                         ByVal pVBHeader As Long, _
                         ByRef pClsid As Any, _
                         ByRef pIID As Any, _
                         ByRef pObject As Any) As Long

' // Modify VBHeader to replace Sub Main
Public Sub ModifyVBHeader(mpVbHeader As Long)
    Dim ptr             As Long
    Dim lOldProtect     As Long
    Dim lFlags          As Long
    Dim lFormsCount     As Long
    Dim lModulesCount   As Long
    Dim lStructSize     As Long
    
    ' // Allow to write to that page
    VirtualProtect ByVal mpVbHeader, &H64, PAGE_EXECUTE_READWRITE, lOldProtect
    
    ' // Remove Sub Main
    ptr = mpVbHeader + &H2C
    GetMem4 0&, ByVal ptr ' 'AddressOf mymain

    VirtualProtect ByVal mpVbHeader, &H64, lOldProtect, 0
    
   

End Sub
Public Function InitVbProjContext1() As IUnknown
    Dim pVBHeader       As Long
    Dim pNewHeader       As Long
    Dim pCOMData        As Long
    Dim lOfstRegInfo    As Long
    Dim pRegInfo        As Long
    Dim pfn             As Long
    Dim hLib            As Long
    Dim iTypes(2)       As Integer
    Dim vParams(2)      As Variant
    Dim lList(2)        As Long
    Dim bIID(1)         As Currency
    Dim cFactory        As IUnknown
    Dim cObject         As IUnknown
    Dim hr              As Long
    Dim vRet            As Variant
    Dim tIID        As tCurGUID
    Dim tClsId      As tCurGUID
    
    hLib = GetModuleHandle(StrPtr("actxdllwithapt_threaded1.dll"))
    MessageBox 0, "aft GetModuleHandle hLib= " & hLib, 0, 0
    pfn = GetProcAddress(hLib, "DllGetClassObject")
    MessageBox 0, "aft GetProcAddress pfn= " & pfn, 0, 0
    If pfn = 0 Then Exit Function
    tIID.c1 = 0.0001@
    tIID.c2 = 504403158265495.5712@
    ' // Get VBHeader
    GetMem4 ByVal pfn + 2, pVBHeader
    MessageBox 0, "aft GetMem4 pVBHeader= " & pVBHeader, 0, 0
    ModifyVBHeader pVBHeader
  
        If pVBHeader Then
    
         VBDllGetClassObject hLib, 0, pVBHeader, tClsId, tIID, 0
        ' MsgBox "VBDllGetClassObject"
        MessageBox 0, "aft VBDllGetClassObject pVBHeader= " & pVBHeader, 0, 0
         
       End If

End Function

Public Function ThreadProc( _
                ByRef tData As tThreadData) As Long
    Dim cExprSrv    As IUnknown
    Dim cInitObj    As IUnknown
    Dim cForm       As Form1
    
    Set cExprSrv = CreateIExprSrvObj(0, 4, 0)
    
    CoInitialize ByVal 0&
    
    Set cInitObj = InitVbProjContext1()
    Set cForm = New Form1
    cForm.Show vbModal
    Set cForm = Nothing
    Set cInitObj = Nothing
    
    CoUninitialize

End Function

When I add athe actx dll (actxdllwithapt_threaded1.dll) thru proj references and call CreateFormofdllinNewThread of Class1 object as follows to std exe (Project1.exe):

Dim x As actxdllwithapt_threaded1.Class1
Private Sub Command1_Click()
Set x = New actxdllwithapt_threaded1.Class1
x.CreateFormofdllinNewThread
End Sub

the std exe crashes when clicked on Command1_Click button.How to make prevent this crash and run the std exe successfully.

std exe (Project1 ) and actx(single threaded) actxdllwithapt_threaded1 projects attached in the same folder.

Thanks