Visual Basic 6 - Any libraries exist to allow implementation of multithreading?

Are there any libraries that I can import into a VB6 project to enable multi threaded support? I know that there are examples using the Windows API but I was wondering if there are any libraries that already exist that I can just import into my project to allow this functionality in VB6. I have inherited a very complex application in VB6 that one of its tasks is to control a multi-million dollar robotic arm. I need to take this application and make some changes that would benefit greatly if I can add multithreaded support. Converting this application to .NET would be an enormous undertaking (to us a good analogy would be the equivalent of a manned mission to Mars next year). The application includes several custom libraries that perform complex scientific calculations and data analysis. The code has been customized to deliver an impressive processing speed (this is VB6). It would take an enormous amount of resources to migrate to a .NET platform. Executive management indicates it could easily be 8 years before the system is upgraded. I would appreciate any responses.

Note: I did a search before submitting this question and I did see a similar question being asked but the answer to the question directs to the Windows API directly. My question is a bit 开发者_JAVA百科different. I am asking about libraries that already include this functionality that I can use in this project. That is, libraries that have already done all this work of using the API.

There's no library for multithreading that I know of. But asynchronous processing does not necessarily require threads. Desaware have StateCoder, a library for state machines which helps with multi-tasking without multi-threading. A bit like the Aysnc CTP.

Alternatively here is a pretty standard scheme for asynchronous background processing in VB6. (For instance it's in Dan Appleman's book and Microsoft's VB6 samples.) You create a separate ActiveX EXE to do the work: that way the work is automatically on another thread, in a separate process (which means you don't have to worry about variables being trampled).

• The VB6 ActiveX EXE object should expose an event CheckQuitDoStuff(). This takes a ByRef Boolean called Quit.
• The client calls StartDoStuff in the ActiveX EXE object. This routine starts a Timer on a hidden form and immediately returns. This unblocks the calling thread. The Timer interval is very short so the Timer event fires quickly.
• The Timer event handler disables the Timer, and then calls back into the ActiveX object DoStuff method. This begins the lengthy processing.
• Periodically the DoStuff method raises the CheckQuitDoStuff event. The client's event handler checks the special flag and sets Quit True if it's necessary to abort. Then DoStuff aborts the calculation and returns early if Quit is True.

This scheme means that the client doesn't actually need to be multi-threaded, since the calling thread doesn't block while "DoStuff" is happening. The tricky part is making sure that DoStuff raises the events at appropriate intervals - too long, and you can't quit when you want to: too short, and you are slowing down DoStuff unecessarily. Also, when DoStuff exits, it must unload the hidden form.

If DoStuff does actually manage to get all the stuff done before being aborted, you can raise a different event to tell the client that the job is finished.

Disclaimer: direct copy of my answer on another question

You can certainly call the windows API to implement multi threading, and its not actually that complicated. However, the simplest solution would be to expose a .net Com object and implement multi threading through .net. For complicated already existing functionality you can break the vb6 app into com libraries that can be called by by the multi threaded .net controller.

[Gui]  ┬> [ .net Com Mulit thread controller]  -> [Com exposed VB 6 utility]
       |
       └> [Com exposed VB 6 utility]

See the article Using Background Threads with Visual Basic 6 for an elegant answer to the problem.

There was a threading library made by elitevb in 2002 which is unfortunately closed now. But there is an archive of elitevb articles on xtremevbtalk. In the section System and devices there is a post at the bottom with the threading.dll and sample source code attached, which makes it very easy to implement threading. As far as I remember, there was the problem, that testing it in the IDE crashed the program, but there were no problems running the compiled program.

With the library, you could create threads pretty straitforward:

Dim ReadValuesThread As Thread

Private Sub Form_Load()
    Set ReadValuesThread = New Thread
    ReadValuesThread.StartThread "ReadValues", "None", Me
    ' Public Function StartThread(FunctionName As String, _
    '                             FunctionParameter As Variant, _
    '                             ParentObject As Object) As Long
End Sub

Private Sub ReadValues()
    ' do things
End Sub

Private Sub Form_Unload(Cancel As Integer)
    ' kill thread
    ReadValuesThread.EndThread
End Sub