# Using a DLL that wants a function pointer **URL:** \ **Category:** Ruby\ **Created:** [January 24, 2008, 4:11pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046 "2008-01-24T16:11:50Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 4:11pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/1 "2008-01-24T16:11:50Z")
I want to use a DLL with Ruby (Win32). This DLL has X number of functions, and one of these takes a function pointer. The DLL will call this callback-function when some data arrives. I cannot figure out how to do this in Ruby. Is it possible? If not, any tips on how to circumvent this restriction? _Any_ hints appreciated. /D ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 7:22pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/2 "2008-01-24T19:22:46Z")
daniel Ã¥kerud wrote: > I want to use a DLL with Ruby (Win32). This DLL has X number of > functions, > and one of these takes a function pointer. The DLL will call this > callback-function when some data arrives. I cannot figure out how to do > this > in Ruby. Is it possible? If not, any tips on how to circumvent this > restriction? _Any_ hints appreciated. It is with fear and trembling that I post here, but I did not want nothing to be said, so take this with the proverbial salt lick until someone that knows can answer. Using pointers from an interpreted language is not something that should work and, if it does, I expect that it will be ugly. Here is what I would do if I had no other way to do, and, at the moment, I don’t. I would make an intermediary program that handles the pointers and talks to both your ruby app and the DLL in question using something simple. You did not say which language the DLL was written in, so I will assume that it is C/C++. Personally, I work with Delphi and a pascal DLL is compiled a bit differently. Also, if it is compiled for windows, they use the FAR PASCAL call to make it run faster, though Mr. Bill changed the name because he hates pascal. You can experiment to find how it all works together but it is at least something. I admit that it is ugly in the extreme, but it is a place to start if nothing more elegant gets offered. GL! ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 7:45pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/3 "2008-01-24T19:45:23Z")
On Jan 24, 9:10 am, daniel åkerud [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > [Note: parts of this message were removed to make it a legal post.] > > I want to use a DLL with Ruby (Win32). This DLL has X number of functions, > and one of these takes a function pointer. The DLL will call this > callback-function when some data arrives. I cannot figure out how to do this > in Ruby. Is it possible? If not, any tips on how to circumvent this > restriction? _Any_ hints appreciated. > > /D I haven’t tried it before, but look into Win32::API::Callback. Most of my googling returned threads where people were having problems with it, but that might give you examples to get started with. Here’s one of them: [http://rubyforge.org/pipermail/win32utils-devel/2008-January/000985.html](http://rubyforge.org/pipermail/win32utils-devel/2008-January/000985.html) Look for where SNMPAPI\_CALLBACK is defined. It appears that Callback takes two arguments - the first is the parameter signature notated the same as when you use an API method. The second would be the return signature. Following that is the body of the callback as a block. ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 9:53pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/4 "2008-01-24T21:53:35Z")
On Jan 24, 2008 9:45 PM, daniel Ã¥kerud [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > in Ruby. Is it possible? If not, any tips on how to circumvent this > > > Look for where SNMPAPI\_CALLBACK is defined. It appears that Callback > > > object. This would work right? I havn’t seen an example of an extension that > > > manages a Proc object though and calls it, but if someone says this sounds > > > reasonable i’ll do this. > > /D I think this is important in this context: The callback is called from another thread, i.e. the DLL creates a thread that reads data in the background, and when data arrives it calls the callback. Would this be a problem if the Ruby extension calls the Proc object from another thread, and if so, how to solve it… /D ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 9:46pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/5 "2008-01-24T21:46:29Z")
On Jan 24, 2008 7:45 PM, yermej [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > same as when you use an API method. The second would be the return > signature. Following that is the body of the callback as a block. Thanks for the answers, Today I have been working with creating Ruby extensions, and I got this idea: What about I pass a Proc.new object to a method in the extension, and when the extension gets a callback from the DLL, it calls the Proc object. This would work right? I havn’t seen an example of an extension that manages a Proc object though and calls it, but if someone says this sounds reasonable i’ll do this. /D ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 10:12pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/6 "2008-01-24T22:12:24Z")
On Jan 24, 1:52 pm, “daniel åkerud” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I think this is important in this context: The callback is called from > another thread, i.e. the DLL creates a thread that reads data in the > background, and when data arrives it calls the callback. Would this be a > problem if the Ruby extension calls the Proc object from another thread, and > if so, how to solve it… At the moment, you don’t. Windows callbacks occur in their own native thread. The Ruby interpreter isn’t thread safe. You’ll get one callback call to work, but after that it will probably segfault. Heesob is working on this for the C side of the house to see if he can come up with a way to make it work. In the meantime, I’m going to see if I can get win32-api ported to JRuby using JNA this weekend. That _should_ work, though it means you’ll have to use JRuby to use it, which may not be such a bad thing. 🙂 Regards, Dan ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 24, 2008, 11:06pm UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/7 "2008-01-24T23:06:57Z")
On Jan 24, 2008 10:11 PM, Daniel B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Regards, > > Dan What if I provide a polling-mechanism, i.e. the Ruby-extension puts all data from the callback in a queue, and the Ruby-script poll()s periodically to see if there is any data. In this case, to Ruby, everything will happen in the same thread. Indeed this removes the callback interface Ruby-Script → Ruby-Extension (which indeed is the subject…), but it circumvents the threading-problem. Would it work? /D ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 25, 2008, 10:29am UTC](https://www.ruby-forum.com/t/using-a-dll-that-wants-a-function-pointer/127046/8 "2008-01-25T10:29:34Z")
daniel åkerud wrote: > > and > > threading-problem. Would it work? > Yes, that would work if you make the data queue thread safe, probably > using a Windows mutex (and wait with no timeout duration in the Ruby > thread). Best regards, Jari W.