I'm currently testing an environment with embedding ruby and found an
issue when allocating a large amount of ruby string objects in external
C calls. Im not sure, whether I misunderstood the correct usage.

The Ruby version used is 1.8.4, own compile on red hat EL update 5.

The C environment is:
---------------------------------
#include "ruby.h"

int main (int argc, char *argv[])
{
    VALUE cModule;
    VALUE message;

    ruby_init();
    cModule = rb_define_module("CModule");

    rb_require("MemCheck.rb");

    for (long long l=0; l<1000LL; l++) {
        // convert C string to Ruby object
        message = rb_str_new2("C says Hello to Ruby."
                              "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                              "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                              "ABCDEFGHIJKLMNOPQRSTUVWXYZ");

        rb_funcall(cModule, rb_intern("sendToRuby"), 1, message);
    }

    return 0;

module CModule
  def CModule.sendToRuby(msgFromC)
  end
end
--------------------------

If I use valgrind to check for memory leaks, all is OK. If I now change
the loop count from 1000LL to 10000LL, valgrind throws errors:

==7903== Conditional jump or move depends on uninitialised value(s)
==7903==    at 0x806C904: gc_mark_children (gc.c:758)
==7903==    by 0x806C88F: gc_mark (gc.c:731)
==7903==    by 0x806C6C2: mark_locations_array (gc.c:626)
==7903==    by 0x806C6EF: rb_gc_mark_locations (gc.c:639)

(in total 496 errors from 39 contexts)

Has anybody seen this behavior? Where am I wrong?

Any help is appreciated, best regards

You'll see similar warnings from valgrind in the presence of other
conservative GCs (for example, the boehm collector for C).

This is a consequence of the fact that a conservative collector must
scan memory without knowing whether it is initialized/valid in
advance or not.  Conservative collectors are designed to be robust
in the face of garbage pointers, however, so this is perfectly
safe.

I was just surprised, that the smaller loop doesn't throw any errors
and as soon as the allocated string objects exceed a given memeory
size, something seems to go wrong. Since Ruby is widely used, that
hinted at an usage error.

Thanks again and best regards,