[geos-devel] An Immodest Proposal

[Chris Hodgson]

Very nice Paul.

Those two std allocs are a bit scary... I had a feeling we might have 
some of those, and they seem worse than I had initially thought. The 
problem is that either they are attempted to be freed, using the 
provided free function - and who knows what error that could bring - or 
they are not, and we're leaking. If they are only created once at load 
of the DLL and never actually freed, but simply go away when the DLL is 
unloaded, then I guess we're ok. But it seems likely to me that the C++ 
runtime would be trying to free them using your own provided free 
function... can we do a test where we provide pfree and see what it does 
with that? ie. if you try to pfree() a regularly malloc()'d segment of 
memory, does it actually free it without raising any errors?

It would be really nice to know what those things that are getting 
created earlier are, too...
but I guess it all just comes down to, does it work in postgres and not 
leak?

Chris

Paul Ramsey wrote:
> It turns out it is a quite small modification, and works pretty well:
>
> http://trac.osgeo.org/geos/attachment/ticket/208/memdiff.patch
>
> My patch adds the ability to override, and also has some printfs to
> show what is happening. When the overridden allocator is called
> without the runtime callback set, it prints "std alloc" and when it's
> called with the callback set, it prints "geos alloc".
>
> Here's a little program that exercises it:
>
> #include <stdio.h>
> #include "/usr/local/include/geos_c.h"
> #include <stdlib.h>
>
> int main() {
>   printf("main\n");
>
>   GEOSCoordSequence* cs;
>   GEOSGeometry* g;
>   int r;
>
>   printf("initgeos\n");
>   initGEOSMemory(malloc, free);
>   printf("coordseqcreate\n");
>   cs = GEOSCoordSeq_create(1, 2);
>   printf("coordseqsetx\n");
>   r = GEOSCoordSeq_setX(cs, 0, 1.0);
>   printf("coordseqsety\n");
>   r = GEOSCoordSeq_setY(cs, 0, 1.0);
>   printf("createpoint\n");
>   g = GEOSGeom_createPoint(cs);
>
>   return 0;
>
> }
>
>
> And here is the output:
>
> Heron:tmp pramsey$ ./a.out
> std alloc!
> std alloc!
> main
> initgeos
> coordseqcreate
> geos alloc!
> geos alloc!
> geos alloc!
> coordseqsetx
> coordseqsety
> createpoint
> geos alloc!
>
> So, something in C++ is doing a couple allocations before we can slip
> in and get our other function in place. But we can get all the big
> stuff caught no problem.
>
> P.
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