Re: garbage collection (was Re: gpfree_string within temp_at())

[Daniel J S. <dan...@ie...>]

Ethan Merritt wrote:
> On Friday 08 July 2005 01:57 am, Dave Denholm wrote:
>>Need to be a little careful with registration of non-trivial objects,
>>to make sure things are atomic wrt SIGINT. 
> 
> 
> That is indeed an issue in principle (but hard to debug I think!).
> 
> New allocations (udv, whole plots, ...) are added at the end of a
> linked list. But this allocate+link operation is not guaranteed 
> atomic by the current code.  I'm not particularly worried by the
> possibily of leaking a single newly-allocated block. But if the
> SIGINT were to occur at just the  wrong time, the final list link
> pointer itself could become corrupt. That would show up as a
> segfault rather than a memory leak.
> 
>    new_element = &(current_end_of_list->next);
>    new_element = gp_alloc(...);
>                     <<<<  SIGINT here is bad news
>    new_element->next = NULL;
> 
> This is fixable, either by careful audit of all the routines that
> do list insertion or by modifying gp_alloc to zero out new space
> before returning it.  

I think the only true way to fix that sort of thing is if SIGINT is disabled before starting the memory allocation and re-enabled after recording the pointer in the linked list.  Otherwise, the same problem can still occur inside gp_alloc() I would think.

Dan