Re[2]: [Gc] Collecting large memory blocks

Ivan Maidanski ivmai at
Wed Dec 2 09:59:25 PST 2009

"Christian Gudrian" <christian at> wrote:
> Am 02.12.2009, 16:01 Uhr, schrieb Ivan Maidanski <ivmai at>:
> > The test work correctly: it prints something near 1.5 MiB. Does this
> > test runs ok on your side?
> Yes.  The heap sizes stays below 2 MiB.
> However, if I execute that loop in a Windows application (using Borland's
> VCL), the heap size goes up to more than 30 MiB.

> Without ALL_INTERIOR_POINTERS it stays below 10 MiB.

This is the key phrase, I think - the data roots (that are scanned by GC) contain values that look like pointers the allocated blocks, so the collector can't recycle them.

Tip: if you have no global pointer variables, you can use the following (to prevent GC from scanning static data roots at all):

int main(void)

If you have a "limited set" of global pointer variables then you can try to inform the collector about them after GC_clear_roots like:

 GC_add_roots(&ptr1_in_data_section, (char*)&ptrN_in_data_section + sizeof(void*));
 GC_add_roots(&ptr1_in_bss_section, (char*)&ptrN_in_bss_section + sizeof(void*));

> How come the collector haves differently depending on the application type
> (console/Windows)?

The collector knows nothing about console/Windows. Check whether the data roots addresses are the same in both cases (and also compare the address of heap (for the allocated objects)).

> Christian


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