Re: [Bug-guile-ncurses] [PATCH 1/2] Add reference count to ITEM structs contained by SCMs

[John Darrington]

On Tue, May 03, 2016 at 02:11:56PM +0000, Mike Gran wrote:
     
     
     
     > On Tuesday, May 3, 2016 5:20 AM, John Darrington <address@hidden> wrote:
     > > This patch (partially) fixes a bug where a segmentation violation in 
the 
     > guile library would occur after, for example the current-item had been 
called.
     > 
     > The problem was, the native C item struct is shared between many SCM 
smobs.
     > Thus, if the garbage collector is allowed to run on any one of them, 
it'll
     > free memory which will later be needed by another.
     > 
     > This patch fixes the problem by using the "userptr" member as a 
     > reference count.
     
     Not too excited about this idea, but, it is better that the present
     condition.

I thought a bit about this.  The only other reasonable solution I could think of
was to keep a hash table.  But that seemed like a lot of effort.   It does mean 
that one cannot use the userptr for any other purpose, but that kind of paradigm
doesn't fit into the scheme way of doing things anyway.

I wasn't too happy about having to cast from pointer to integer and back again.

     
     I'll push after I've written a test case for the test suite.

Writing a reproducible test case is hard because the GC being a conservative
one, one can't force it to do anyting.  But perhaps you're better at it
than I am.
     
J'

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