COM - what does _pAtlModule->Lock() lock exactly?

Question

I'm working my way through learning writing a COM control. I've got an example project, and it uses the lines

_pAtlModule->Lock()
_pAtlModule->Unlock()

in the OnCreate() handler and the OnDestroy() handler for the COM control respectively.

I realise that the _pAtlModule is an instance of the CAtlModule - the "application" object (for want of a better description ).

But to my question. What exactly does _pAtlModule->Lock() lock? I know it's a critical section, but what is it protecting?

Must I Lock and Unlock the _pAtlModule object when writing my COM controls?

thanks!

Answer 1

On the outsude, it doesn't actually appear to do anything substantial!

MSDN says "It increases the Lock count and returns the updated value; This may be useful for debugging and tracing".

http://msdn.microsoft.com/en-US/library/9syc2105%28v=VS.80%29.aspx

I think this is misleading however, the behavior is intended to stop the module from being unloaded. I theorize it's some atomic value that's used as a lock anchor (for want of a better term!).

Answer 2

See this answer to a similar question This function is for managing so-called "lock count" of the in-proc COM server DLL. Together with DllCanUloadNow() the lock count prevents the DLL from being unloaded until its code and data is of no use anymore.