Hi.

I would like to pass a Dbisam Dataset as parameter in function call in DLL.
I have already set this up with a DLL that is dynamically loaded and
unloaded.
However I get an AV when closing my application, and in some way it seems to
have a relation to handeling of the dataset that was passed with the
function.
I can do iterations of the datasets, but not gather data from the datasets
(FieldByName).

Is using datasets passed as parameters a wise approach?

Petter Topp
Dbisam4

Petter


Its a long time since I used DLLs so I may be wrong but my memory is that the DLL and the main process for the application don't share the same memory space. What I remember doing was having the datamodule in the DLL and passing string parameters across to identify the table and record I wanted.

If you want to share access to tables etc you have to use packages not DLLs.

Roy Lambert [Team Elevate]

Hi Roy.

As you may have understood - it's simply a very convenient way to go...
I will have a look at using a dynamic array to pass along key values of data
to be worked on, or simply sharing a table for this purpose...

Petter


"Roy Lambert"  skrev i nyhetsmeldingen:
CD1E98E0-CACA-4BB6-A35A-062E31EA52EC@news.elevatesoft.com ...

Petter


Its a long time since I used DLLs so I may be wrong but my memory is that
the DLL and the main process for the application don't share the same memory
space. What I remember doing was having the datamodule in the DLL and
passing string parameters across to identify the table and record I wanted.

If you want to share access to tables etc you have to use packages not DLLs.

Roy Lambert [Team Elevate]

Petter


If its something you're going to do much I'd investigate packages. The other question to ask yourself is "why use a DLL?" Way back it made sense because of memory restrictions now I just don't bother and have some monstrous .exes (up to 35Mb whilst in development with debug code).

I just had a quick browse on the web and found

http://wwv.comanswer.com/question/delphi-dll-form-communication
(this one surprised me because it says the dll and application share the same memory space - my memory must be wrong)

http://www.delphipages.com/articles/delphi_memory_monitor-9225.html
(this one suggests memory mapped files as a good way to communicate)


There are also some good threads on the CodeGear ngs eg:

https://forums.embarcadero.com/thread.jspa?messageID=216034&tstart=0#216034

Roy Lambert [Team Elevate]

Petter,

<< I would like to pass a Dbisam Dataset as parameter in function call in
DLL. >>

Unfortunately, you cannot do so.  As Roy indicated, you can use packages to
do so, but not DLLs.  The reason for this restriction is that the .exe and
..dll have different virtual method tables for classes, and so they cannot
understand each other's object layouts.  With packages, the virtual method
tables are all located in one place.  This is the reason for the rule that
once you use packages, you cannot have the same code in a package and
compiled into the .exe.

--
Tim Young
Elevate Software
www.elevatesoft.com

Roy,

<< (this one surprised me because it says the dll and application share the
same memory space - my memory must be wrong) >>

They share the same memory space (and with Delphi can even share the same
memory manager), but they can't understand each other's classes, so they
don't know how to deal with an object instance from the other.  This is why
simple types work fine as parameters to a DLL, but object instances do not.

--
Tim Young
Elevate Software
www.elevatesoft.com

Tim

>They share the same memory space (and with Delphi can even share the same
>memory manager), but they can't understand each other's classes, so they
>don't know how to deal with an object instance from the other. This is why
>simple types work fine as parameters to a DLL, but object instances do not.

So why was it you could pass ShortStrings but not strings?

Roy Lambert

Hi Guys.

Thanks for very useful information.
Based on this info I have decided to go the safe way - adding a datamodule
to the DLL and "share" needed information throgh Dbisam.
And just for the record - I'm also happy with just deploying large exe
applications, but sometimes it's very convenient to just upgrade a module of
the app that are more exposed to outside changes.

"Petter Topp"  skrev i nyhetsmeldingen:
E1CEA262-97F5-462A-858F-71CCA358F06F@news.elevatesoft.com ...

Hi.

I would like to pass a Dbisam Dataset as parameter in function call in DLL.
I have already set this up with a DLL that is dynamically loaded and
unloaded.
However I get an AV when closing my application, and in some way it seems to
have a relation to handeling of the dataset that was passed with the
function.
I can do iterations of the datasets, but not gather data from the datasets
(FieldByName).

Is using datasets passed as parameters a wise approach?

Petter Topp
Dbisam4

Roy,

<< So why was it you could pass ShortStrings but not strings? >>

I think you can pass long strings also, if you use the shared memory manager
(FastMM4).   The reason that short strings work is that they are not
(normally) dynamically-allocated and aren't reference-counted, and therefore
don't need to know from whence they came like long strings.  When you assign
a short string to another short string, you're copying the entire string
from one memory location to the other.

--
Tim Young
Elevate Software
www.elevatesoft.com