It may or may not be useful to you, but when I am dealing with DLL's,
I use this simple unit that I've written once:
unit untDLL;
interface
uses Windows;
type
IDLL = interface(IUnknown)
['{D1CB2BE4-7183-41EF-852F-8B9AE377444C}']
function GetProcAddress(ProcName: string): FARPROC;
function Handle: THandle;
function Name: string;
end;
function NewDLL(const Filename: string): IDLL;
implementation
uses SysUtils;
type
TDLL = class(TInterfacedObject, IDLL)
private
FHandle: THandle;
protected // IDLL
function GetProcAddress(ProcName: string): FARPROC;
function Handle: THandle;
function Name: string;
public
constructor Create(const Filename: string);
destructor Destroy; override;
end;
function NewDLL(const Filename: string): IDLL;
begin
Result := TDLL.Create(Filename);
end;
constructor TDLL.Create(const Filename: string);
begin
inherited Create;
FHandle := LoadLibrary(PChar(Filename));
if (FHandle = 0) then raise
Exception.Create(SysErrorMessage(GetLastError));
end;
destructor TDLL.Destroy;
begin
try
if (FHandle <> 0) then FreeLibrary(FHandle);
finally inherited;
end;
end;
function TDLL.GetProcAddress(ProcName: string): FARPROC;
begin
Result := Windows.GetProcAddress(FHandle, PChar(ProcName));
if (Result = nil) then raise
Exception.Create(SysErrorMessage(GetLastError));
end;
function TDLL.Handle: THandle;
begin
Result := FHandle;
end;
function TDLL.Name: string;
begin
Result := GetModuleName(FHandle);
end;
end.
(Removed blank lines to make this email smaller.)
Now, the usage is very simple. I just declare a variable (DLL) of type
IDLL and then use: DLL := NewDLL('Somefile.dll');
This either results in an exception or it will work. I can then call
DLL.GetProcAddress('Method') with just the name of the procedure or
function that I need.
The advantage of this interface is that when I assign nil or another
NewDLL object to the DLL variable, then it will unload the DLL
automatically. And of course, if the DLL variable is a local variable
then it will also unload the DLL when the variable goes out of scope.
(In other words, the Delphi Garbage collection will clean it.)
So far I haven't had any problems working with DLL's this way.
Now the trick is, of course, to avoid having to reread those methods
every time. So basically, after loading the DLL you should just get
all the addresses of procedures that you want to call and store them.
And maybe, if you like, you could add a special event to this
interface that will clear all those procedure variables for you when
your DLL is released.
One other advantage is that you can pass this DLL object to any other
function or procedure without having to worry about when you have to
release it. The reference counter in the object will release it once
the last reference to the object is nil'ed. In other words, this is a
good way to keep a DLL in memory for as long as you need it, and not
much longer...
With kind regards,
X Katja Bergman.
--- In [email protected], "Chris @ IT" <[EMAIL PROTECTED]> wrote:
> Hi All,
>
> I have this application that loads DLL's dynamically as plugins and
as such
> I use the loadlibrary, getprocaddress, free library routines.
>
> The host application loads the dll and calls its process export
function so
> that the dll can do what its meant to do. The problem is there are
usually
> many requests to be done (about 500 every second) and when I call
the dll
> for each sequentially its takes quite a bit of time
>
> What I want to try is spawn a new thread that loads the dll and
calls the
> function. With this approach the dll will be loaded many times and its
> function called many times.
>
> Anything I should know about calling dlls in this manner? All dlls
and apps
> written in Delphi 7
>
> Chris.
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