Dynamic Link Library & Function Pointers

[AdrianLP]

Hello all. I'm writing a Push To Talk radio program. As such I have a DLL that uses SetWindowsHookEx to set a callback function. This works, and is called when keyboard events take place.

Client programs using this DLL wish to know when a keyboard event takes place (even if said client program is not in the foreground).

So in my DLL I store a function pointer in a shared data section), and the DLL allows the clients to pass in a function pointer to be called when a keyboard event is raised.

If the client program has focus, the callback works as expected. If the client does not have focus, the callback method is called but never returns. I suspect this is because the client's function is in a different address space then all the DLL instances except the one it explicitly creates.

So my question is, how do you send data from a DLL to a client which may not have focus? Is a pipe the best bet?

[AdrianLP]

...I hope this isn't off topic as it refers to DLLs. I would not find a Windows-specific programming forum on this site.

I suspect this question is less about DLLs and more about how to share data between applications using C++ (but perhaps even that is OS-specific) :(

[weaknessforcats]

This is covered in Windows via C/C++ by Jeffrey Richter 2008.

The aopplications are separate processes ?? Or os one a child proecess of the other?

Most likely, you will use a mutex.

[AdrianLP]

This is covered in Windows via C/C++ by Jeffrey Richter 2008.

The aopplications are separate processes ?? Or os one a child proecess of the other?

Most likely, you will use a mutex.

There is one client, and it uses LoadLibrary to get the DLL (which installs a global keyboard hook).

As long as the client is in focus, the DLL can call a callback function which the client provides it with. If however the client is not in focus, the callback never returns.

The trouble is, what I understand from the MSDN, the DLL is duplicated many times (once for each running application) to handle the keyboard hooking. Only one instance has access to the callback method though.

[weaknessforcats]

Focus may not be the issue. Are the Windows on separate threads?

I expect they will have to be to support multi-processing.