[geos-devel] Memory Leak In GEOSIntersection_r

[Mick Orridge]

On Thu, Feb 12, 2015 at 3:35 PM, Sandro Santilli <strk at keybit.net> wrote:

> On Sat, Jan 24, 2015 at 12:41:28AM +0000, Mick Orridge wrote:
> > This is my first post here, so feel free to let me know if I should
> > be doing things differently.
> >
> > I've been using the nightly snapshot from 4/1/2015 to generate
> > Voronoi polygons and then clip them to the UK coastline on Windows
> > 8.1 with VS2013. After processing several 100,000 polygons with
> > GEOSIntersection_r my laptop was running out of memory.
> >
> > I've investigated further and it looks like the Edges rejected by
> > OverlayOp::insertUniqueEdges in OverlayOp.cpp are not being deleted.
>
> I think they are deleted later. If you hadn't seen this yet please
> provide a testcase showing the leak. See tests/unit/capi/ for a good
> start.
>

Finally found some time to look at this. I have a testcase that can be
added to test/unit/capi and it can be downloaded here:-
http://www.gismosoftware.co.uk/download.php. I can post it to the list if
that's better (either as an attachment or in-line). The problem occurs in
test 4; when you have a multipolygon and a polygon within it where it's
envelope  doesn't intersect the other other polygon

eg.

geom1_ = GEOSGeomFromWKT("MULTIPOLYGON(((0 0,5 10,10 0,0 0),(1 1,1 2,2 2,2
1,1 1),(100 100,100 102,102 102,102 100,100 100)))");
geom2_ = GEOSGeomFromWKT("POLYGON((0 1,0 2,10 2,10 1,0 1))");

geom3_ = GEOSIntersection(geom1_, geom2_);

This causes the continue statement in OverlayOp::insertUniqueEdges to be
hit and then these edges are never deleted.

Here's the object dump from Visual Studio:-

Detected memory leaks!
Dumping objects ->
D:\src\Lib\Geos\geos-20141225\src\geomgraph\Edge.cpp(305) : {10223} normal
block at 0x000000469FEE2670, 32 bytes long.
 Data: <      Y@      Y@> 00 00 00 00 00 00 59 40 00 00 00 00 00 80 59 40
{10055} normal block at 0x000000469FED8E60, 16 bytes long.
 Data: <    F           > E0 8A ED 9F 46 00 00 00 00 00 00 00 00 00 00 00
{10054} normal block at 0x000000469FED8DD0, 40 bytes long.
 Data: <    F       F   > D0 8D ED 9F 46 00 00 00 D0 8D ED 9F 46 00 00 00
{10053} normal block at 0x000000469FED8C70, 16 bytes long.
 Data: <p   F           > 70 8A ED 9F 46 00 00 00 00 00 00 00 00 00 00 00
{10052} normal block at 0x000000469FED8D60, 12 bytes long.
 Data: <            > FF FF FF FF FF FF FF FF FF FF FF FF
{10049} normal block at 0x000000469FED8CF0, 12 bytes long.
 Data: <            > 01 00 00 00 00 00 00 00 02 00 00 00
{10046} normal block at 0x000000469FED8BF0, 16 bytes long.
 Data: <H   F           > 48 8A ED 9F 46 00 00 00 00 00 00 00 00 00 00 00
{10045} normal block at 0x000000469FED8B70, 16 bytes long.
 Data: <(   F           > 28 8A ED 9F 46 00 00 00 00 00 00 00 00 00 00 00
D:\src\Lib\Geos\geos-20141225\src\geomgraph\EdgeIntersectionList.cpp(220) :
{10044} normal block at 0x000000469FED8A20, 224 bytes long.
 Data: <`a3H    p   F   > 60 61 33 48 F9 7F 00 00 70 8B ED 9F 46 00 00 00
D:\src\Lib\Geos\geos-20141225\src\geomgraph\EdgeIntersectionList.cpp(211) :
{10043} normal block at 0x000000469FED89A0, 24 bytes long.
 Data: <  1H        F   > D0 EA 31 48 F9 7F 00 00 B0 87 ED 9F 46 00 00 00
{10042} normal block at 0x000000469FED88C0, 120 bytes long.
 Data: <      Y@      Y@> 00 00 00 00 00 00 59 40 00 00 00 00 00 00 59 40
{10041} normal block at 0x000000469FED8840, 16 bytes long.
 Data: <    F           > B0 87 ED 9F 46 00 00 00 00 00 00 00 00 00 00 00
D:\src\Lib\Geos\geos-20141225\src\geomgraph\EdgeIntersectionList.cpp(190) :
{10040} normal block at 0x000000469FED87B0, 32 bytes long.
 Data: <@   F       F   > 40 88 ED 9F 46 00 00 00 C0 88 ED 9F 46 00 00 00
D:\src\Lib\Geos\geos-20141225\src\geom\GeometryFactory.cpp(96) : {6995}
normal block at 0x000000469FECF060, 16 bytes long.
 Data: <                > 01 00 00 00 CD CD CD CD 00 00 00 00 00 00 00 00
D:\src\Lib\Geos\geos-20141225\src\geom\GeometryFactory.cpp(740) : {6994}
normal block at 0x000000469FECEFD0, 32 bytes long.
 Data: <  2H    `   F   > 90 AC 32 48 F9 7F 00 00 60 F0 EC 9F 46 00 00 00
Object dump complete.


The "Data:" memory blocks are owned by the leaked Edge but I haven't add
the code to trace them (but they do get deleted if you delete the edge as
per the deleteOrphanedEdges described in my original e-mail)

If you remove the ",(100 100,100 102,102 102,102 100,100 100)" from the
MULTIPOLYGON all but the GeometryFactory.cpp leaks disappear.


The fix I suggested with deleteOrphanedEdges breaks the GEOSPointOnSurface
test 4. This is because the 4th edge is collapsed in
OverlayOp::replaceCollapsedEdges (in OverlayOp::computeOverlay) which then
deletes the old edge, but it does not reset the pointer to null
for baseSplitEdges so this is left pointing at the deleted edge (which
causes an access violation for env->intersects(...)  in
deleteOrphanedEdges). I don't understand the relationship between
baseSplitEdges and the member variable edgeList so I don't really know what
to suggest here.


> > There is also a small memory leak of a geomFactory in
> > init/finishGEOS(). The only way I can see to fix this is to
> > introduce a reference count and then null the static pointer when it
> > reaches 0. Happy to have a look at fixing this if this seems a
> > reasonable approach.
>
> I think that one is not important. IIRC it once was a class-static
> and could be deleted by the Unload class, not sure if that's still the
> case.
>

 Agreed that it's not important.

Regards,

Mick Orridge

http://www.gismosoftware.co.uk
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