Two blitz apps communicating

Is there an efficient way for two separate Blitz programs to communicate?

I wan't my game to have two separate threads, a client and a server sending data packets back and forth. In connections through WAN I would use TCP or UDP, but when playing the game on single machine, using network to communicate is strange. I wouldn't want to use that if I don't really need to.

Blitz functions that haven't catched my eye? Windows API functions?

Of course if blitz3d supports multithreading, that would be solution, but I haven't found any info on that.

The Windows window message WM_COPYDATA is built specifically for that... you may need to write a DLL for it to work happily, though. It is in User32, sent by SendMessage in the Windows API.

I used UDP to send commands between two editors for a game I was making on the same machine (one written in blitzplus other written in blitz3d) with no problems. What is the reason you wish to not use networking commands?

User could have the whole network service disabled, but this is of course a rare case.

Using user32 sounds good, but a bit complicated. I wonder how fast it is compared to having both stuff in one exe? Writing DLL's is new to me and I have no tools make them. If this gets too difficult, I'll probably use UDP first and implement WM_COPYDATA later if needed. Or?

Imlementing UDP properly may take as much time as doing the WM_COPYDATA thing. It is very useful because you'll learn how to use Windoes Api functions using Blitz userlib declarations.

I don't know exactly about WM_COPYDATA, but usually you only need to write a DLL because Blitz doesn't support Pointers. But with a little hack this can be solved nevertheless:

In the "userlibs" folder needs to be a file named "kernel32.decls" containing at least the following lines:

api_RtlMoveMemory(Destination*,Source,Length) : "RtlMoveMemory"

In the Blitz App you'll then be able to find out the physical adress of a bank this sway:

mybank=createbank(256)
pointer =AddressOf(mybank)
...
Function AddressOf(Bank) ; Find the correct Adress of a Bank (for C *Pointer)
Local Address = CreateBank(4) 
api_RtlMoveMemory(Address,Bank+4,4) 
Return PeekInt(Address,0) 
End Function

Im pretty sure this WM_COPYDATA function requires such a pointer to write the Data to. An other reason why it could fail is Memory protection.

Well, not sure of this, tho I managed to use a lot of Api calls directly from within blitz where other coders used to write DLLs for.