From: Josh Huber <huber+rt@...>
Date: 2004-03-11T12:50:02+09:00
Subject: A few questions about Ruby/DL

I've had quite good luck using Ruby/DL to wrap a shared library, but
the lack of documentation in english is possibly preventing me from
using it in the best way.

I have a few questions:

1. Memory management -- how do I free memory?  When do I need to free
   memory?  I can't seem to find any free's in the examples, but
   there are references to setting a freeing function in the PtrData
   class documentation (ext/dl/doc/dl.txt)

2. What's the best way to handle pointer outputs which allocate
   memory?  I've done things like the following, but I'm not sure
   that it's the best way:

   # say the C interface has a prototype like

   # int get_data(char **data, int *len);

   # on success, memory is allocated for a string and the pointer is
   # assigned to the data parameter.  The length of the string is
   # written into the len parameter.

   data = DL::malloc(DL::sizeof("P"))
   len  = DL::malloc(DL::sizeof("L"))
   len.struct!("L", "val")

   ret  = LIB.get_data(data, len)

   if ret == LIB::STATUS_OK
     puts "got a string of length #{len[:val]}: #{data.ptr}"
   else
     puts "failed to get data: #{LIB::strerror(ret)}"
   end

So, my questions are:

in the above example, is there a more elegant way to deal with output
strings/data structures, etc, and how to I free the memory associated
with the output string?  Is there any way for GC to know if the
memory is allocated dynamically or statically?  What if the library
is responsible for freeing the memory?  (clearly, I don't know enough
about GC)

Thanks for the help,

-- 
Josh Huber