DirectCom.dll implementation

[smkperu]

Hello Olaf,

I have gone thru your VB6ThreadingDirectCOM sample https://www.vbforums.com/showthread....-dll-HelperLib
which is really awesome.

Can you provide source code for the exported functions say STARTCOMOBJECT of DirectCom.dll c/c++ dll so that I can improve my understanding of COM using c/c++.

Thanks

[Schmidt]

It's the standard CreateThread-API-Call which is happening there basically...

And in the ThreadCallback-Function the usual things happen.
- Take the passed UDT-Pointer from the "UserParam" (priorily passed into CreateThread)
- Read out: DllName, ClassName, "Users-UserParam" from the UDT-Fields inside this new Thread
- initialize the Thread for COM-STA-Mode
- create an STA-ClassInstance regfree (from DllName, ClassName)
- enter the Thread-MessageLoop and stay there (until notice from the "controlling Class on the outside")

On Startup (from the outside), the UDT is filled from inside a Helper-Class cThreadHandler -
which will be returned by this Function - and runs on the MainThread (allowing interaction with the started Thread).

And that's it - not Rocket-Science.

Olaf

[smkperu]

Dear Olaf,

Thanks for the clarification.
I understood your explanation even better when I came across your another awesome pure
VB6 Threading-Tutorial (Mandelbrot-Rendering) at the link
https://www.vbforums.com/showthread....rot-Rendering) at Step7 StdExe (using STA-Dll).

More or less both VB6ThreadingDirectCOM and VB6 Threading-Tutorial (Mandelbrot-Rendering) at the link
https://www.vbforums.com/showthread....rot-Rendering) at Step7 StdExe (using STA-Dll) are same except
that VB6ThreadingDirectCOM is using c/c++ dll (DirectCom.dll) for creating the STA thread.

The beauty of VB6ThreadingDirectCOM is that it works fine even when the project is compiled to p-code(both std exe app and STA dll app) and works even when run in vb6 IDE.

But Step7 StdExe (using STA-Dll) of VB6 Threading-Tutorial (Mandelbrot-Rendering) crashes when run outside or in vb6 IDE when compiled to p-code.

Is there any reason for this since I don't have this problem when working in pure c/c++ applications in which i never come across p-code option while compiling in vc++ IDE like in vb6 IDE.


Thanks.

[Schmidt]

https://www.vbforums.com/showthread....rot-Rendering)

at Step7 StdExe (using STA-Dll) ... crashes when run outside or in vb6 IDE when compiled to p-code.

Is there any reason for this since I don't have this problem when working in pure c/c++ applications in which i never come across p-code option while compiling in vc++ IDE like in vb6 IDE.

We are not allowed to call any vbRuntime-Functions from within the ThreadCallback until STA-instance-creation took place.
(that's the reason for using a *.tlb to call "other APIs").

And when in PCode-Mode - it seems not even the little trick with the *.tlb-based API-calls
(this way avoiding Err.LastDllError interactions) is sufficient because the "Runtime is touched anyways"...

And yes, there's of course no PCode-option in C/C++ compilers -
and, if "native-VB6-compilation" solves the issue in VB6 - why not keep it this way (it's the default).

Olaf

[smkperu]

Dear Olaf,

Thanks for the clarification.
I understood your explanation even better when I came across your another awesome pure
VB6 Threading-Tutorial (Mandelbrot-Rendering) at the link
https://www.vbforums.com/showthread....rot-Rendering) at Step7 StdExe (using STA-Dll).

More or less both VB6ThreadingDirectCOM and VB6 Threading-Tutorial (Mandelbrot-Rendering) at the link
https://www.vbforums.com/showthread....rot-Rendering) at Step7 StdExe (using STA-Dll) are same except
that VB6ThreadingDirectCOM is using c/c++ dll (DirectCom.dll) for creating the STA thread.

The beauty of VB6ThreadingDirectCOM is that it works fine even when the project is compiled to p-code(both std exe app and STA dll app) and works even when run in vb6 IDE.

But Step7 StdExe (using STA-Dll) of VB6 Threading-Tutorial (Mandelbrot-Rendering) crashes when run outside or in vb6 IDE when compiled to p-code.

Is there any reason for this since I don't have this problem when working in pure c/c++ applications in which i never come across p-code option while compiling in vc++ IDE like in vb6 IDE.


Thanks.

Hello Olaf,

Now I understood that vb6 native code is the default option we can use in vb6.
You mean there is no way to bypass runtime in pcode in threadcallback like using .tlb in native code.
Then for what other purpose is this extra pcode option available in vb6 IDE.

Thanks

[wqweto]

Then for what other purpose is this extra pcode option available in vb6 IDE.

It's the other way around -- p-code compiled binaries were first intoduced in VB3 (or earlier) and it was in VB5 that native binaries become available.

They left p-code binaries for compatibility reasons, besides it makes no sense to remove it when thay *had* to support p-code interpreter for IDE debugging etc. interactions which cannot be replaced by any compiled code (incl. native compiled one).

cheers,
</wqw>

p.s. I already told you p-code multi-threading is not possible and now you know the reason -- the p-code interpreter is not thread-safe, not only the runtime is not thread-safe which can be circumvented with TLB usage.

[smkperu]

Dear wqweto and Olaf,

Now I have understood better and mark the thread as resolved.

Thanks