[VB6] - Module for working with multithreading.

[The trick]

lowe517, you can't call the methods of an object between threads without marshaling. You can pass the socket handle between threads so you can create an auxiliary object which lives in the thread. See the example.

[lowe517]

lowe517, you can't call the methods of an object between threads without marshaling. You can pass the socket handle between threads so you can create an auxiliary object which lives in the thread. See the example.

Thanks! I 'll check this out

[lowe517]

Dear The trick,
I find that I can do the some work using VBCreatethread, as well as using a private object as your example showed,all I need to do is that I dim an object(cTCPClient) in the threadFunc and after its method calling I free it. the object exists only in the threadfunc, everything seems all right, but is there anything potentially wrong ?

[The trick]

Dear The trick,
I find that I can do the some work using VBCreatethread, as well as using a private object as your example showed,all I need to do is that I dim an object(cTCPClient) in the threadFunc and after its method calling I free it. the object exists only in the threadfunc, everything seems all right, but is there anything potentially wrong ?

The main restriction you shouldn't pass an object reference between threads. The other point is you should track the data and synchronize access. The rules are the same if you would work in C/C++.

[fafalone]

So I'm trying to follow how this all works but it's quite difficult, so sorry if this is a stupid question, but will threads created in this manner terminate normally, when the Thread Proc completes? As in, I can duplicate the handle and use WaitOnSingleObject, and expect it terminate as expected when the thread proc exits?

[The trick]

So I'm trying to follow how this all works but it's quite difficult, so sorry if this is a stupid question, but will threads created in this manner terminate normally, when the Thread Proc completes? As in, I can duplicate the handle and use WaitOnSingleObject, and expect it terminate as expected when the thread proc exits?

When you use vbCreateThread it's the same like you use CreateThread-API. It returns a Win32 handle you can pass to other APIs. And yes the threads terminate normally.

[vbwins]

Hi Trick,

I am using the version below. When I create more than one thread AND i run my projects in WinDbg I get a crash inside

Private Function ThreadProc( _
                 ByVal pParameter As Long) As Long

Attachment 186145

It only seems to happen inside WinDbg when I have created two threads. It does not seem to happen outside WinDbg but this may be a timing issue. I have included a screen shot of the stack.

Perhaps you have some idea what is happening?

EDIT - I take it back. It does happen outside WinDbg

EDIT EDIT - It does happen outside WinDbg but not reliably. Sometimes its fine.

' //
' // modMultiThreading2.bas - The module provides support for multi-threading.
' // Version 2.1
' // © Krivous Anatoly Anatolevich (The trick), 2015-2019
' // No TLB, No additional DLLs, No Asm-thunks (in compiled form)
' // Private object creation based on NameBasedObjectFactory by firehacker

[vbwins]

It may be my fault. I was calling this in the startup for each thread right before vbCreateThread. If I only call it once it seems fine.

Public Function Initialize() As Boolean
10        On Error GoTo errorHandler
          
          Dim bIsInIDE As Boolean
          
20        Debug.Assert MakeTrue(bIsInIDE)
                    

40        If Not bIsInIDE Then
                           
50            If Not tLockMarshal.bIsInitialized Then
              
60               writeAgentLog "INFORMATION - Initialized Marshal lock"
                 
70               InitializeCriticalSection tLockMarshal.tWinApiSection
              
80               tLockMarshal.bIsInitialized = True
              
90            End If
              
100           If Not tLockHeap.bIsInitialized Then
              
110              writeAgentLog "INFORMATION - Initialized heap lock"
              
120              InitializeCriticalSection tLockHeap.tWinApiSection
              
130              tLockHeap.bIsInitialized = True
              
140           End If
              
150           hModule = App.hInstance
              
160           pVBHeader = GetVBHeader()
              
170           If pVBHeader = 0 Then GoTo CleanUp
                            
180           ModifyVBHeader AddressOf FakeMain
              
190           hHeadersHeap = HeapCreate(0, 0, 65536)
              
200           If hHeadersHeap = 0 Then GoTo CleanUp

210       End If
          
220       lTlsSlot = TlsAlloc()
          
230       If lTlsSlot = TLS_OUT_OF_INDEXES Then GoTo CleanUp
          
          ' // Main thread already initialized
240       TlsSetValue lTlsSlot, ByVal 1&
          
250       Initialize = True
          
CleanUp:

300       If Not Initialize Then
          
             'writeAgentLog "Calling uninitialize"
             
310          Uninitialize
              
320       End If
          
330       Exit Function
          

End Function

[The trick]

You should call Initialize once. Attach your project with error.

[vbwins]

Unfortunately I can't attach the project. Calling initialize once solved the problem. Thanks Andrew

[Chris_G33]

Thanks a lot for the multithreading files.

However, I have a problem with it:
It works only when compiling to system code
When compiling to p-code the exe it seems hangs when the thread is started and the crashses (the window just closes).

I have a large project and when compiling it to systerm code I get a linker error:
........Form....frm(-22483) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'E:\8783\vc98\p2\src\P2\main.c', line 494)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more information

I have no idea how to solve that.

Any chance the multithreading will work with p-code?

thanks, Chris

[wqweto]

There is no way to implement in-proc multi-threading with p-code compiled modules either using this submission or any other one because the p-code interpreter is not thread safe.

In your case if you *have* to use in-proc multi-threading (this or other impl) there is no other way for this than to fix the internal compiler error by figuring out what is causing it in your VB6 project.

It is either targeting p-code and forget about in-proc multi-threading, fix internal compiler error and use in-proc multi-threading or try using ActiveX EXEs i.e. out-of-proc multi-threading w/ p-code.

cheers,
</wqw>

[Chris_G33]

Thanks for the quick reply.
It seems I have to find out what line is causing the linker error.

Or does this work with an active x dll in p code?

Is there a thread about difference between p-code and native code?
E.g.
For i = 0 to ubound(List())
Next
hangs in the for loop when compiling to native code and List() is empty, but with compiled to p-code it works fine.
When On Error Resume Next is used

Other such known differences?

[wqweto]

Other such known differences?

Why do you think this is a known difference? Is there a list of known differences you are looking at which has this one listed there?

Better ask in the main forum if someone (who cares about these differences) knows anything might chime in because this thread is about multi-threading.

cheers,
</wqw>

[Chris_G33]

No, I do not have a list. I just wanted to know if there is such a list (and gave an example) before starting a new thread.

[SuperDre]

Why would you want compiled to p-Code in the first place? what's the benifits over compiling to native code (as p-code is a lot slower as native)?

[Chris_G33]

Why would you want compiled to p-Code in the first place? what's the benifits over compiling to native code (as p-code is a lot slower as native)?

P-Code:
- Smaller files
- im my experience not really much slower, maybe some %
- faster compiling
- I had problems with native code some years ago (cant remember details) and with p-code it was working fine.
And now I have that damn compiler error, still after 2 hours changing code etc.
Maybe the compiler has a problem in a form with more than ~49000 lines.

[fafalone]

Smaller files?? P-code always makes substantially larger files for me, usually at least 2-3x the size.

[Chris_G33]

P-Code file are usually factor 2-2.5 smaller than file in native code.

I now found this thread here:
https://www.vbforums.com/showthread....us-Native-Code
with a project with multithreading working with p-code. Well, not really, crashes when thread is finished.

[fafalone]

Checked more samples and it's all over the map... pcode is ranging from half the size, to very close (most common), to 4 bigger

[Schmidt]

Checked more samples and it's all over the map... pcode is ranging from half the size, to very close (most common), to 4 bigger

I think it's safe to say that, when we compile "code-only" Projects (like e.g. Ax-Dlls),
PCode produces "roughly half the size" compared to NativeCode.

In your 1:1 cases there's probably "a lot of Bitmaps and Icons" embedded
(coming from visual-resource-parts as *.frx or *.ctx,
making the PCode-savings insignificant compared to the resource-volume)...

And your case where PCode is 4 times larger might be related to Typelib-embedding?
Never investigated that, but PCode might embed a referenced *.tlb in its entirety -
whereas native-compiles "embed only the needed parts of a typelib"?

Olaf

[Chris_G33]

I now got one project working.
Thanks again for this great piece of code.

My exe is now 16 MB (native code) instead of 6 MB (p code).

My other project with the "fatal error C1001: INTERNAL COMPILER ERROR": I moved some routines to another bas file. Now it compiles. But the exe just quits after some seconds. I need to investigate further.

(It seems for the line number a signed 16bit integer, as the line number of my error message was Form....frm(-22483)), though the line number was -22483 + 65536 = 43053.)

[The trick]

The linker can remove unused code from executables (native-code) whenas P-code saves everything. So if you use an universal standard module with bunch of functions and use few ones the native code can have smaller size.

[Chris_G33]

I now have the problem that my exe sometimes terminates when a thread ends.
Any idea how to solve that?

[wqweto]

I now have the problem that my exe sometimes terminates when a thread ends.
Any idea how to solve that?

You have to *manually* release global state i.e. private and public variable of Object and String type in a .bas module has to be cleared (set to Nothing or vbNullString) in ThreadProc before calling CoUninitialize and subsequenctly returning execution to OS.

This is practically impossible with static "local" variables in procedures so in-proc mutli-threading in VB6 is doomed unless threaded lightly by the app. developers themselves (take care of every wrinkle introduced).

Another thing which might help if you are using Ax DLL for the in-proc is to enable Retained in Memory in project settings though I wouldn't hold my breath.

cheers,
</wqw>

[Chris_G33]

You have to *manually* release global state i.e. private and public variable of Object and String type in a .bas module has to be cleared (set to Nothing or vbNullString) in ThreadProc before calling CoUninitialize and subsequenctly returning execution to OS.

This is practically impossible with static "local" variables in procedures so in-proc mutli-threading in VB6 is doomed unless threaded lightly by the app. developers themselves (take care of every wrinkle introduced).
cheers,
</wqw>

Thanks for the answer.

But, can you please clarify this.

1. clear private strings and objects, ok. Why only in bas modukes, but not in Forms?

2. public strings:
Do i have to clear them only when they are set/modified in a thread? Or when they are only accessed by reading them, too?

[The trick]

I now have the problem that my exe sometimes terminates when a thread ends.
Any idea how to solve that?

Attach your project exe or attach a crash dump.

[Chris_G33]

Attach your project exe or attach a crash dump.

From the event log, thats all I have, There is no crash message.
- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
<Provider Name="Application Error" Guid="{a0e9b465-b939-57d7-b27d-95d8e925ff57}" />
<EventID>1000</EventID>
<Version>0</Version>
<Level>2</Level>
<Task>100</Task>
<Opcode>0</Opcode>
<Keywords>0x8000000000000000</Keywords>
<TimeCreated SystemTime="2023-03-27T15:34:56.7881203Z" />
<EventRecordID>41944</EventRecordID>
<Correlation />
<Execution ProcessID="24792" ThreadID="10068" />
<Channel>Application</Channel>
<Computer>NewTowerWork</Computer>
<Security UserID="S-1-5-21-245563044-3042615410-272610636-1001" />
</System>
- <EventData>
<Data Name="AppName">My.exe</Data>
<Data Name="AppVersion">5.3.0.652</Data>
<Data Name="AppTimeStamp">6421b786</Data>
<Data Name="ModuleName">MSVBVM60.DLL</Data>
<Data Name="ModuleVersion">6.0.98.48</Data>
<Data Name="ModuleTimeStamp">5ea8e7bc</Data>
<Data Name="ExceptionCode">c0000005</Data>
<Data Name="FaultingOffset">00020f36</Data>
<Data Name="ProcessId">0x5a4c</Data>
<Data Name="ProcessCreationTime">0x1d960c1a8c52a49</Data>
<Data Name="AppPath">P:\Projects\6Vb6\My.exe</Data>
<Data Name="ModulePath">C:\WINDOWS\SYSTEM32\MSVBVM60.DLL</Data>
<Data Name="IntegratorReportId">964bd0eb-4527-45b5-a0a8-1e5c71d86a74</Data>
<Data Name="PackageFullName" />
<Data Name="PackageRelativeAppId" />
</EventData>
</Event>

[The trick]

I suppose (according to your log) you call Uninitialize when you have worked threads. So you should either wait until the threads end or don't call Uninitialize at all.

[Chris_G33]

I suppose (according to your log) you call Uninitialize when you have worked threads. So you should either wait until the threads end or don't call Uninitialize at all.

Yeah, you are absolutely right! Thanks a lot!

[Chris_G33]

When I need to transfer data in strings from a thread to the main thread, i see these options:

1. a public String variable in a form

2. a textfield control in a form

3. a string with fixed length

4. a public string, which I prealloc in the main thread e.g. with mystring = String$(1000, 0) and in the the thread I copy a local string to that string using the StrPtr


Is this correct?

[The trick]

When I need to transfer data in strings from a thread to the main thread, i see these options:

1. a public String variable in a form

2. a textfield control in a form

3. a string with fixed length

4. a public string, which I prealloc in the main thread e.g. with mystring = String$(1000, 0) and in the the thread I copy a local string to that string using the StrPtr


Is this correct?

See AsynchDispMethodCall. It accepts a callback method which is called when the method is done. You can see the examples there are many callback examples.

[Chris_G33]

I now have another issue/question.

The created threads are working fine multithreadwise.
But not the main thread and the created threads. Only one of the is active, either the main thread or the created threads.

e.g.

Sub Test()
Dim i As Long
vbCreateThread 0, 0, AddressOf MyThread1, 0, 0, 0
vbCreateThread 0, 0, AddressOf MyThread2, 0, 0, 0

for i = 0 to 10
    sleep 100
next
End Sub

MyThread1 and MyThread2 are not started after calling vbCreateThread, they are called when the procedure Test is finished and the main thread gets idle. Of course, I could add some DoEvents, but then still, either the main thread OR the created threads are executed.
Why is that so?
Is there a way to have full multithreading here, too?

Thank you, Chris

[The trick]

Make a small demo. Probably the child threads wait for main thread being idle like marshaling things etc.

[Chris_G33]

Make a small demo. Probably the child threads wait for main thread being idle like marshaling things etc.

project attached.
List1 is filled first (main thread), then list 2 and 3 simultaneously (2 created threads)

[The trick]

You have a bug with marshaling. You can't just access to an object from an arbitrary thread. You should use marshaling always to avoid the bugs in future. The behavior of your code is explained by the fact that you call Form1.Text2.Text = "Thread 1: " & CStr(GetCurrentThreadId()) & vbNewLine and Form1.Text3.Text = "Thread 2: " & CStr(GetCurrentThreadId()) & vbNewLine which just call SetWindowText that calls SendMessage WM_SETTEXT. SendMessage waits until the window process the message in main thread.

[Chris_G33]

You have a bug with marshaling. You can't just access to an object from an arbitrary thread. You should use marshaling always to avoid the bugs in future. The behavior of your code is explained by the fact that you call Form1.Text2.Text = "Thread 1: " & CStr(GetCurrentThreadId()) & vbNewLine and Form1.Text3.Text = "Thread 2: " & CStr(GetCurrentThreadId()) & vbNewLine which just call SetWindowText that calls SendMessage WM_SETTEXT. SendMessage waits until the window process the message in main thread.

Thanks for your anwer.
I tried with
MultiThreading.EnablePrivateMarshaling True
but no change.
What do I have to change in my example code? I don't know mashalling in VB6.

So, if do not do GUI stuff it should work.

[The trick]

Thanks for your anwer.
I tried with
MultiThreading.EnablePrivateMarshaling True
but no change.
What do I have to change in my example code? I don't know mashalling in VB6.

So, if do not do GUI stuff it should work.

You should use Marshal/Unmarshal functions to pass an object between threads (read the description). You can't use your code because to set form's caption you should message pump in the form's thread. The same behavior you will see in any other language.

[smkperu]

Hello Trick,

I wanted to use atlsimpleobjforvb simpleobject from Atlsimpleobjdeno atl project using CreateActiveXObjectInNewThread2 of modMultiThreading2.bas as follows by adding atl dll project thru references:

Dim x As ATLSIMPLEOBJDENOLib.atlsimpleobjforvb
Private Sub Command1_Click()
Dim cObj    As Object
Dim asyncid As Long
Set cObj = CreateActiveXObjectInNewThread2("ATLSIMPLEOBJDENOLib.atlsimpleobjforvb", , asyncid)  'fails with Invalid procedure call or argument error

cObj.method1
End Sub

Private Sub Form_Load()
modMultiThreading.Initialize
End Sub

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

when I add atl project thru references to vb st exe projectI run the project I get msgbox with the following error.

---------------------------
Project1
---------------------------
Run-time error '5':

Invalid procedure call or argument
---------------------------
OK
---------------------------

Both Atl dll and vb6 std exe projects attached

How to create atl simple object in the vb client and call its method method1 without error.

Thanks

[The trick]

Hello Trick,

I wanted to use atlsimpleobjforvb simpleobject from Atlsimpleobjdeno atl project using CreateActiveXObjectInNewThread2 of modMultiThreading2.bas as follows by adding atl dll project thru references:

Dim x As ATLSIMPLEOBJDENOLib.atlsimpleobjforvb
Private Sub Command1_Click()
Dim cObj    As Object
Dim asyncid As Long
Set cObj = CreateActiveXObjectInNewThread2("ATLSIMPLEOBJDENOLib.atlsimpleobjforvb", , asyncid)  'fails with Invalid procedure call or argument error

cObj.method1
End Sub

Private Sub Form_Load()
modMultiThreading.Initialize
End Sub

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

when I add atl project thru references to vb st exe projectI run the project I get msgbox with the following error.

---------------------------
Project1
---------------------------
Run-time error '5':

Invalid procedure call or argument
---------------------------
OK
---------------------------

Both Atl dll and vb6 std exe projects attached

How to create atl simple object in the vb client and call its method method1 without error.

Thanks

Why did you add "lib"?

Set x = CreateActiveXObjectInNewThread2("ATLSIMPLEOBJDENO.atlsimpleobjforvb", , asyncid)