lwgeom_geos_prepared.c

Go to the documentation of this file.

/**********************************************************************
 *
 * PostGIS - Spatial Types for PostgreSQL
 * http://postgis.net
 *
 * PostGIS is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * PostGIS is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with PostGIS.  If not, see <http://www.gnu.org/licenses/>.
 *
 **********************************************************************
 *
 * Copyright (C) 2012 Sandro Santilli <strk@kbt.io>
 * Copyright (C) 2008 Paul Ramsey <pramsey@cleverelephant.ca>
 * Copyright (C) 2007 Refractions Research Inc.
 *
 **********************************************************************/
 
 
#include <assert.h>
 
#include "../postgis_config.h"
#include "lwgeom_geos_prepared.h"
#include "lwgeom_cache.h"
 
/***********************************************************************
**
**  PreparedGeometry implementations that cache intermediate indexed versions
**  of geometry in a special MemoryContext for re-used by future function
**  invocations.
**
**  By creating a memory context to hold the GEOS PreparedGeometry and Geometry
**  and making it a child of the fmgr memory context, we can get the memory held
**  by the GEOS objects released when the memory context delete callback is
**  invoked by the parent context.
**
**  Working parts:
**
**  PrepGeomCache, the actual struct that holds the keys we compare
**  to determine if our cache is stale, and references to the GEOS
**  objects used in computations.
**
**  PrepGeomHash, a global hash table that uses a MemoryContext as
**  key and returns a structure holding references to the GEOS
**  objects used in computations.
**
**  PreparedCacheContextMethods, a set of callback functions that
**  get hooked into a MemoryContext that is in turn used as a
**  key in the PrepGeomHash.
**
**  All this is to allow us to clean up external malloc'ed objects
**  (the GEOS Geometry and PreparedGeometry) before the structure
**  that references them (PrepGeomCache) is pfree'd by PgSQL. The
**  methods in the PreparedCacheContext are called just before the
**  function context is freed, allowing us to look up the references
**  in the PrepGeomHash and free them before the function context
**  is freed.
**
**/
 
/*
** Backend prepared hash table
**
** The memory context call-backs use a MemoryContext as the parameter
** so we need to map that over to actual references to GEOS objects to
** delete.
**
** This hash table stores a key/value pair of MemoryContext/Geom* objects.
*/
static HTAB* PrepGeomHash = NULL;
 
#define PREPARED_BACKEND_HASH_SIZE      32
 
typedef struct
{
        MemoryContext context;
        const GEOSPreparedGeometry* prepared_geom;
        const GEOSGeometry* geom;
}
PrepGeomHashEntry;
 
/* Memory context hash table function prototypes */
uint32 mcxt_ptr_hasha(const void *key, Size keysize);
static void CreatePrepGeomHash(void);
static void AddPrepGeomHashEntry(PrepGeomHashEntry pghe);
static PrepGeomHashEntry *GetPrepGeomHashEntry(MemoryContext mcxt);
static void DeletePrepGeomHashEntry(MemoryContext mcxt);
 
 
static void
PreparedCacheDelete(void *ptr)
{
        MemoryContext context = (MemoryContext)ptr;
 
        PrepGeomHashEntry* pghe;
 
        /* Lookup the hash entry pointer in the global hash table so we can free it */
        pghe = GetPrepGeomHashEntry(context);
 
        if (!pghe)
                elog(ERROR, "PreparedCacheDelete: Trying to delete non-existent hash entry object with MemoryContext key (%p)", (void *)context);
 
        POSTGIS_DEBUGF(3, "deleting geom object (%p) and prepared geom object (%p) with MemoryContext key (%p)", pghe->geom, pghe->prepared_geom, context);
 
        /* Free them */
        if ( pghe->prepared_geom )
                GEOSPreparedGeom_destroy( pghe->prepared_geom );
        if ( pghe->geom )
                GEOSGeom_destroy( (GEOSGeometry *)pghe->geom );
 
        /* Remove the hash entry as it is no longer needed */
        DeletePrepGeomHashEntry(context);
}
 
 
/* TODO: put this in common are for both transform and prepared
** mcxt_ptr_hash
** Build a key from a pointer and a size value.
*/
uint32
mcxt_ptr_hasha(const void *key, Size keysize)
{
        uint32 hashval;
 
        hashval = DatumGetUInt32(hash_any(key, keysize));
 
        return hashval;
}
 
static void
CreatePrepGeomHash(void)
{
        HASHCTL ctl;
 
        ctl.keysize = sizeof(MemoryContext);
        ctl.entrysize = sizeof(PrepGeomHashEntry);
        ctl.hash = mcxt_ptr_hasha;
 
        PrepGeomHash = hash_create("PostGIS Prepared Geometry Backend MemoryContext Hash", PREPARED_BACKEND_HASH_SIZE, &ctl, (HASH_ELEM | HASH_FUNCTION));
}
 
static void
AddPrepGeomHashEntry(PrepGeomHashEntry pghe)
{
        bool found;
        void **key;
        PrepGeomHashEntry *he;
 
        /* The hash key is the MemoryContext pointer */
        key = (void *)&(pghe.context);
 
        he = (PrepGeomHashEntry *) hash_search(PrepGeomHash, key, HASH_ENTER, &found);
        if (!found)
        {
                /* Insert the entry into the new hash element */
                he->context = pghe.context;
                he->geom = pghe.geom;
                he->prepared_geom = pghe.prepared_geom;
        }
        else
        {
                elog(ERROR, "AddPrepGeomHashEntry: This memory context is already in use! (%p)", (void *)pghe.context);
        }
}
 
static PrepGeomHashEntry*
GetPrepGeomHashEntry(MemoryContext mcxt)
{
        void **key;
        PrepGeomHashEntry *he;
 
        /* The hash key is the MemoryContext pointer */
        key = (void *)&mcxt;
 
        /* Return the projection object from the hash */
        he = (PrepGeomHashEntry *) hash_search(PrepGeomHash, key, HASH_FIND, NULL);
 
        return he;
}
 
 
static void
DeletePrepGeomHashEntry(MemoryContext mcxt)
{
        void **key;
        PrepGeomHashEntry *he;
 
        /* The hash key is the MemoryContext pointer */
        key = (void *)&mcxt;
 
        /* Delete the projection object from the hash */
        he = (PrepGeomHashEntry *) hash_search(PrepGeomHash, key, HASH_REMOVE, NULL);
 
        if (!he)
        {
                elog(ERROR, "DeletePrepGeomHashEntry: There was an error removing the geometry object from this MemoryContext (%p)", (void *)mcxt);
        }
 
        he->prepared_geom = NULL;
        he->geom = NULL;
}
 
static int
PrepGeomCacheBuilder(const LWGEOM *lwgeom, GeomCache *cache)
{
        PrepGeomCache* prepcache = (PrepGeomCache*)cache;
        PrepGeomHashEntry* pghe;
 
        /*
        * First time through? allocate the global hash.
        */
        if (!PrepGeomHash)
                CreatePrepGeomHash();
 
        /*
        * No callback entry for this statement context yet? Set it up
        */
        if ( ! prepcache->context_callback )
        {
                PrepGeomHashEntry pghe;
                MemoryContextCallback *callback;
                prepcache->context_callback = AllocSetContextCreate(prepcache->context_statement,
                                           "PostGIS Prepared Geometry Context",
                                           ALLOCSET_SMALL_SIZES);
 
                /* PgSQL comments suggest allocating callback in the context */
                /* being managed, so that the callback object gets cleaned along with */
                /* the context */
                callback = MemoryContextAlloc(prepcache->context_callback, sizeof(MemoryContextCallback));
                callback->arg = (void*)(prepcache->context_callback);
                callback->func = PreparedCacheDelete;
                MemoryContextRegisterResetCallback(prepcache->context_callback, callback);
 
                pghe.context = prepcache->context_callback;
                pghe.geom = 0;
                pghe.prepared_geom = 0;
                AddPrepGeomHashEntry( pghe );
        }
 
        /*
        * Hum, we shouldn't be asked to build a new cache on top of
        * an existing one. Error.
        */
        if ( prepcache->gcache.argnum || prepcache->geom || prepcache->prepared_geom )
        {
                lwpgerror("PrepGeomCacheBuilder asked to build new prepcache where one already exists.");
                return LW_FAILURE;
    }
 
        prepcache->geom = LWGEOM2GEOS( lwgeom , 0);
        if ( ! prepcache->geom ) return LW_FAILURE;
        prepcache->prepared_geom = GEOSPrepare( prepcache->geom );
        if ( ! prepcache->prepared_geom ) return LW_FAILURE;
        prepcache->gcache.argnum = cache->argnum;
 
        /*
        * In order to find the objects we need to destroy, we keep
        * extra references in a global hash object.
        */
        pghe = GetPrepGeomHashEntry(prepcache->context_callback);
        if ( ! pghe )
        {
                lwpgerror("PrepGeomCacheBuilder failed to find hash entry for context %p", prepcache->context_callback);
                return LW_FAILURE;
        }
 
        pghe->geom = prepcache->geom;
        pghe->prepared_geom = prepcache->prepared_geom;
 
        return LW_SUCCESS;
}
 
static int
PrepGeomCacheCleaner(GeomCache *cache)
{
        PrepGeomHashEntry* pghe = 0;
        PrepGeomCache* prepcache = (PrepGeomCache*)cache;
 
        if ( ! prepcache )
                return LW_FAILURE;
 
        /*
        * Clear out the references to the soon-to-be-freed GEOS objects
        * from the callback hash entry
        */
        pghe = GetPrepGeomHashEntry(prepcache->context_callback);
        if ( ! pghe )
        {
                lwpgerror("PrepGeomCacheCleaner failed to find hash entry for context %p", prepcache->context_callback);
                return LW_FAILURE;
        }
        pghe->geom = 0;
        pghe->prepared_geom = 0;
 
        /*
        * Free the GEOS objects and free the index tree
        */
        POSTGIS_DEBUGF(3, "PrepGeomCacheFreeer: freeing %p argnum %d", prepcache, prepcache->gcache.argnum);
        GEOSPreparedGeom_destroy( prepcache->prepared_geom );
        GEOSGeom_destroy( (GEOSGeometry *)prepcache->geom );
        prepcache->gcache.argnum = 0;
        prepcache->prepared_geom = 0;
        prepcache->geom = 0;
 
        return LW_SUCCESS;
}
 
static GeomCache*
PrepGeomCacheAllocator()
{
        PrepGeomCache* prepcache = palloc(sizeof(PrepGeomCache));
        memset(prepcache, 0, sizeof(PrepGeomCache));
        prepcache->context_statement = CurrentMemoryContext;
        prepcache->gcache.type = PREP_CACHE_ENTRY;
        return (GeomCache*)prepcache;
}
 
static GeomCacheMethods PrepGeomCacheMethods =
{
        PREP_CACHE_ENTRY,
        PrepGeomCacheBuilder,
        PrepGeomCacheCleaner,
        PrepGeomCacheAllocator
};
 
 
PrepGeomCache *
GetPrepGeomCache(FunctionCallInfo fcinfo, SHARED_GSERIALIZED *g1, SHARED_GSERIALIZED *g2)
{
        return (PrepGeomCache*)GetGeomCache(fcinfo, &PrepGeomCacheMethods, g1, g2);
}