Delphi DllMain DLL_PROCESS_DETACH called before DLL_PROCESS_ATTACH

Question

I'm having a lot of trouble dealing with a DLL I've written in Delphi. I've set up a DllMain function using the following code in the library: ``` begin DllProc := DllMain; end. ``` My `DllMain` procedure looks like this: ``` procedure DllMain(reason: Integer); begin if reason = DLL_PROCESS_DETACH then OutputDebugString('DLL PROCESS DETACH') else if reason = DLL_PROCESS_ATTACH then OutputDebugString('DLL PROCESS ATTACH') else if reason = DLL_THREAD_ATTACH then OutputDebugString('DLL THREAD ATTACH') else if reason = DLL_THREAD_DETACH then OutputDebugString('DLL THREAD DETACH') else OutputDebugString('DllMain'); end; ``` What I'm finding is that DETACH seems to be called (twice?!) by a caller (that I don't control) before ATTACH is ever called. Is that even possible, or am I misunderstanding how this is supposed to work? My expectation would be that every ATTACH call would be met with a matching DETACH call, but that doesn't appear to be the case. What's goin' on here?!

Accepted Answer

Unfortunately when `begin` is executed in your dll code, the OS has already called `DllMain` in your library. So when your `DllProc := DllMain;` statement executes it is already too late. The Delphi compiler does not allow user code to execute when the dll is attached to a process. The suggested workaround (if you can call that a workaround) is to call your own `DllMain` function yourself in a unit initalization section or in the library code:

```
begin
  DllProc := DllMain;
  DllMain(DLL_PROCESS_ATTACH);
end;
```

The relevant documentation:

Note: DLL_PROCESS_ATTACH is passed to the procedure only if the DLL's initialization code calls the procedure and specifies DLL_PROCESS_ATTACH as a parameter.

Delphi DllMain DLL_PROCESS_DETACH called before DLL_PROCESS_ATTACH

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