Solved

Memory mapped files troubles

Posted on 2003-11-26
4
1,090 Views
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!
0
Comment
Question by:SpiderVenom
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
4 Comments
 
LVL 6

Accepted Solution

by:
GloomyFriar earned 125 total points
ID: 9831382
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.
0
 
LVL 1

Expert Comment

by:pucko
ID: 25505444
Hmm force accept on a Question the same day?
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction Raise your hands if you were as upset with FireMonkey as I was when I discovered that there was no TListview.  I use TListView in almost all of my applications I've written, and I was not going to compromise by resorting to TStringGrid…
In my programming career I have only very rarely run into situations where operator overloading would be of any use in my work.  Normally those situations involved math with either overly large numbers (hundreds of thousands of digits or accuracy re…
There are cases when e.g. an IT administrator wants to have full access and view into selected mailboxes on Exchange server, directly from his own email account in Outlook or Outlook Web Access. This proves useful when for example administrator want…
Do you want to know how to make a graph with Microsoft Access? First, create a query with the data for the chart. Then make a blank form and add a chart control. This video also shows how to change what data is displayed on the graph as well as form…

696 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question