[Cffi-devel] foreign-free causes stack dump (on CCL) after a repeated calls

[Mirko Vukovic]

Problem solved - A buffer length was not properly initialized.

On Mon, Feb 9, 2015 at 3:50 PM, Mirko Vukovic <mirko.vukovic at gmail.com>
wrote:

> Hello,
>
> I am running 64-bit CCL 1.10 on Windows 7.  I'm writing an interface to a
> National Instruments library (dll)
> The library was downloaded from the NI site.  It was compiled using
> Microsofts C++ compiler.
>
> I get a stack dump when a pointer is being freed using foreign-free.  This
> error occurs not in a fresh lisp
> session, but after a second or third call to the same function (with same
> arguments).
>
> One more detail: the library is used to access data in files in NI's TDMS
> format.  This error does not
> seem to happen on all files that I am trying to access, only some of them.
>
> I don't have much experience in cross-language library interface building,
> and I am wondering if I am making
> some kind of mistake.  I am hoping for pointers on how to debug this
> further.
>
> I define a pointer of type :uint to access results of a call to a library
> function that places them into an
> unsigned int variable.  I then retrieve the value using using mem-ref, and
> the free the pointer.
> This is where the stack dump happens.
>
> What follows is the defcfun, and the lisp function.  I mark with *** the
> pointer, and the relevant variable
> definitions that pertain to it:
>
> The C-function interface (with the C-documentation included) is
> (defcfun (ddc-get-num-channel-group-properties
> "DDC_GetNumChannelGroupProperties")
>     ddc-code
>   "
> This function will get numberOfProperites (via a pointer)
>
> int DDC_GetNumChannelGroupProperties (DDCChannelGroupHandle channelGroup,
>                                       unsigned int *numberOfProperties);
> *******"
>   (group-handle group-handle) ;; group-handle is define to be a pointer
> type
>   (num-channel-group-properties :pointer)) ;;*******
>
> The pointer issue arises with the second variable
> num-channel-group-properties.
>
> The lisp code where the error occurs is below (relevant lines highlighted
> with ***).
>
> (defun get-num-channel-group-properties (group-handle*)
>   "Get number of file properties
>
> FILE-HANDLE* is a pointer to the file handle"
> ;;  (trace foreign-alloc)
>   (let ((number-of-properties
>        (let ((number-of-properties* (foreign-alloc :uint))) ;;******
>          (print 'allocated-pointer)
>          (print number-of-properties*)
>          (ddc-get-num-channel-group-properties group-handle*
>                            number-of-properties*)
>          (print 'done-with-ddc)
>          (prog2
>          (print 'acessing-number-of-properties)
>          (mem-ref number-of-properties* :uint) ;; ********
>            (print 'freeing-pointer)
>            (foreign-free number-of-properties*) ;; ********
>            (print 'freed-pointer)))))
>   ;;  (untrace foreign-alloc)
>     (print 'ready-to-return-with-value)
>     number-of-properties))
>
> The traceback is:
>
> ALLOCATED-POINTER
> #<A Foreign Pointer #x5FFC70>
> DONE-WITH-DDC
> ACESSING-NUMBER-OF-PROPERTIES
> FREEING-POINTER
>  1> Calling (FOREIGN-FREE #<A Foreign Pointer #x5FFC70>)
>
> and the debugger traceback is
>
> (#x0000000026479810) #x00000000000F532C : #<Function FREE
> #x00000001000F51BF> + 365
> (#x0000000026479840) #x0000000001491314 : #<Function (TRACED FOREIGN-FREE)
> #x000000210149109F> + 629
> (#x0000000026479888) #x000000000139DE14 : #<Function
> GET-NUM-CHANNEL-GROUP-PROPERTIES #x000000210139DCDF> + 309
>
> So, to summarize:
>
> I have created a pointer to access results of a library call.  Library
> accesses contents of files created with National
> Instruments software.  Library is compiled with MS C++.
>
> The pointer free crash occurs on the third call of the lisp function.  The
> first two calls (with same arguments)
> run OK.
>
> Thanks,
>
> Mirko
>
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