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Memory mapped files troubles

Posted on 2003-11-26
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Last Modified: 2007-12-19
I’m having a bit of trouble with a dll that uses memory mapped files. Since my application must receive key presses when out of focus, I used a small bit of delphi code I found on the net to build a keyhook. The dll in in the apps resources as a piece of rcdata, and is unpacked to a temporary file, then loaded, and finally deleted when the app is done. Or it should be. If I just open the app, then close it, the file is deleted fine. But if I trigger a keypress, then close it, nu-uh. After reading the sdk doc for DeleteFile, I figured it was the memory mapped files doing this. But I can’t figure what I am doing wrong. Here’s the applicable code:

{ Dll loading code }

var
    DllHandle, MemFile: THandle;
    Receiver: PHandle;
    HookOn, HookOff: procedure; stdcall;

...

  MemFile := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0, SizeOf(Integer), 'KeyReceiver');
  if (MemFile = 0) then
    raise Exception.Create('Error while creating file');

  Receiver := MapViewOfFile(MemFile, FILE_MAP_WRITE, 0, 0, 0);
  Receiver^ := Handle;

  // Load the keyhook
  DllHandle := LoadLibrary(PChar(DllFile)); //DllFile contains the temp name
  if DllHandle = 0 then
    raise Exception.Create('Unable to load the required DLL');

  @HookOn := GetProcAddress(DllHandle, '_HookOn@0');
  @HookOff := GetProcAddress(DllHandle, '_HookOff@0');
  if (not Assigned(HookOn)) or (not Assigned(HookOff)) then
    raise Exception.Create('Unable to locate the required DLL functions');

  HookOn;

Here’s the DLL init code:

HHOOK Keybrd;
HANDLE MemFile, DllInst;
HWND *Receiver;

...

  switch (ul_reason_for_call)
  {
    case DLL_PROCESS_ATTACH:
      DllInst = hModule;
      MemFile = OpenFileMapping(FILE_MAP_READ, FALSE, "KeyReceiver");
      if (MemFile != 0)
        Receiver = MapViewOfFile(MemFile, FILE_MAP_READ, 0, 0, 0);      
      break;
    case DLL_PROCESS_DETACH:
      if (MemFile != 0) {
        UnmapViewOfFile(Receiver);
        CloseHandle(MemFile);
      }
      break;
  }

Hook activation code:

Keybrd = SetWindowsHookEx(WH_KEYBOARD, &HookCallBack, DllInst, 0);

Deactivation code:

UnhookWindowsHookEx(Keybrd);

The code to send a message to the app:

  if (Code == HC_ACTION)
    PostMessage(*Receiver, CM_SEND_KEY, wParam, lParam);

  return CallNextHookEx(Keybrd, Code, wParam, lParam);

And the code that frees the app’s vars and deletes (or tries to) the dll:

  if Assigned(HookOff) then
    HookOff;

  if (DllHandle > 0) then
    FreeLibrary(DllHandle);

  if (MemFile > 0) then begin
    UnmapViewOfFile(Receiver);
    CloseHandle(MemFile);
  end;

  if FileExists(DllFile) then
    DeleteFile(DllFile);

The most I can find is that windows reports Access is denied when it tries to delete the file (if I have pressed a key, if not, it deletes fine). Also, the file can be deleted manually once the app is closed.

If any more info is needed, just say.

Thanks!
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Question by:SpiderVenom
4 Comments
 
LVL 6

Accepted Solution

by:
GloomyFriar earned 125 total points
Comment Utility
Does the DllFile contain right pathname at the error point?
If so, then someone is using the dll and that is why you can't delete it.
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Expert Comment

by:pucko
Comment Utility
Hmm force accept on a Question the same day?
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