resource.c

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2011-2014, VU University Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

#include "rdf_db.h"
#include "murmur.h"

static functor_t FUNCTOR_literal1;

static int
init_resource_hash(resource_db *rdb)
{ size_t bytes = sizeof(resource**)*INITIAL_RESOURCE_TABLE_SIZE;
  resource **r = rdf_malloc(rdb->db, bytes);
  int i, count = INITIAL_RESOURCE_TABLE_SIZE;

  memset(r, 0, bytes);
  for(i=0; i<MSB(count); i++)
    rdb->hash.blocks[i] = r;

  rdb->hash.bucket_count       = count;
  rdb->hash.bucket_count_epoch = count;
  rdb->hash.count              = 0;

  return TRUE;
}


static void
free_resource_chain(rdf_db *db, resource *r)
{ resource *n;

  for(; r; r=n)
  { n = r->next;
    PL_unregister_atom(r->name);
    rdf_free(db, r, sizeof(*r));
  }
}

static void
free_resource_chains(rdf_db *db, resource **rl, int count)
{ int i;

  for(i=0; i<count; i++)
    free_resource_chain(db, rl[i]);

  rdf_free(db, rl, sizeof(resource**)*count);
}

static void
erase_resource_hash(resource_db *rdb)
{ if ( rdb->hash.blocks[0] )
  { int i, count = INITIAL_RESOURCE_TABLE_SIZE;

    free_resource_chains(rdb->db, rdb->hash.blocks[0], count);

    for(i=MSB(count); i<MAX_RBLOCKS; i++)
    { resource **r = rdb->hash.blocks[i];

      if ( r )
      { int size = BLOCKLEN(i);

	r += size;
	free_resource_chains(rdb->db, r, size);
      } else
	break;
    }
  }

  memset(&rdb->hash, 0, sizeof(rdb->hash));
}


static int
resize_resource_table(resource_db *rdb)
{ int i = MSB(rdb->hash.bucket_count);
  size_t bytes  = sizeof(resource**)*rdb->hash.bucket_count;
  resource **r = rdf_malloc(rdb->db, bytes);

  memset(r, 0, bytes);
  rdb->hash.blocks[i] = r-rdb->hash.bucket_count;
  rdb->hash.bucket_count *= 2;
  DEBUG(1, Sdprintf("Resized resource table to %ld\n",
		    (long)rdb->hash.bucket_count));

  return TRUE;
}


int
init_resource_db(rdf_db *db, resource_db *rdb)
{ rdb->db = db;
  init_resource_hash(rdb);

  return TRUE;
}


void
erase_resources(resource_db *rdb)
{ erase_resource_hash(rdb);
}


typedef struct res_walker
{ resource_db  *rdb;			/* Resource DB */
  atom_t	name;			/* Name of the resource */
  size_t	unbounded_hash;		/* Atom's hash */
  size_t	bcount;			/* current bucket count */
  resource     *current;		/* current location */
} res_walker;


static void
init_res_walker(res_walker *rw, resource_db *rdb, atom_t name)
{ rw->rdb	     = rdb;
  rw->name	     = name;
  rw->unbounded_hash = atom_hash(name, MURMUR_SEED);
  rw->bcount	     = rdb->hash.bucket_count_epoch;
  rw->current	     = NULL;
}


static resource*
next_resource(res_walker *rw)
{ resource *r;

  if ( rw->current )
  { r = rw->current;
    rw->current = r->next;
  } else if ( rw->bcount <= rw->rdb->hash.bucket_count )
  { do
    { size_t entry = rw->unbounded_hash % rw->bcount;
      r = rw->rdb->hash.blocks[MSB(entry)][entry];
      rw->bcount *= 2;
    } while(!r && rw->bcount <= rw->rdb->hash.bucket_count );

    if ( r )
      rw->current = r->next;
  } else
    return NULL;

  return r;
}


static resource *
existing_resource(resource_db *rdb, atom_t name)
{ res_walker rw;
  resource *r;

  init_res_walker(&rw, rdb, name);
  while((r=next_resource(&rw)))
  { if ( r->name == name )
      return r;
  }

  return NULL;
}


resource *
lookup_resource(resource_db *rdb, atom_t name)
{ resource *r, **rp;
  int entry;

  if ( (r=existing_resource(rdb, name)) )
    return r;

  LOCK_MISC(rdb->db);
  if ( (r=existing_resource(rdb, name)) )
  { UNLOCK_MISC(rdb->db);
    return r;
  }

  r = rdf_malloc(rdb->db, sizeof(*r));
  memset(r, 0, sizeof(*r));
  r->name = name;
  PL_register_atom(name);
  if ( rdb->hash.count > rdb->hash.bucket_count )
    resize_resource_table(rdb);
  entry = atom_hash(name, MURMUR_SEED) % rdb->hash.bucket_count;
  rp = &rdb->hash.blocks[MSB(entry)][entry];
  r->next = *rp;
  *rp = r;
  rdb->hash.count++;
  UNLOCK_MISC(rdb->db);

  return r;
}


resource *
register_resource(resource_db *rdb, atom_t name)
{ resource *r = lookup_resource(rdb, name);

  assert(r);
  ATOMIC_INC(&r->references);

  return r;
}


resource *
unregister_resource(resource_db *rdb, atom_t name)
{ resource *r = existing_resource(rdb, name);

  ATOMIC_DEC(&r->references);

  return r;
}



		 /*******************************
		 *	       PROLOG		*
		 *******************************/

typedef struct res_enum
{ resource_db *rdb;
  resource    *current;
  int	       current_entry;
} res_enum;


static foreign_t
rdf_resource(term_t r, control_t h)
{ rdf_db *db = rdf_current_db();
  res_enum *state;

  switch( PL_foreign_control(h) )
  { case PL_FIRST_CALL:
    { atom_t name;

      if ( PL_is_variable(r) )
      { state = PL_malloc_uncollectable(sizeof(*state));
	state->rdb = &db->resources;
	state->current = NULL;
	state->current_entry = -1;
	break;
      } else if ( PL_get_atom(r, &name) )
      { resource *r;

	if ( (r=existing_resource(&db->resources, name)) &&
	     r->references > 0
	   )
	  return TRUE;
	return FALSE;
      } else if ( PL_is_functor(r, FUNCTOR_literal1) )
	return FALSE;

      return PL_type_error("atom", r);
    }
    case PL_REDO:
      state = PL_foreign_context_address(h);
      break;
    case PL_PRUNED:
      state = PL_foreign_context_address(h);
      rdf_free(db, state, sizeof(*state));
      return TRUE;
    default:
      assert(0);
      return FALSE;
  }

  for(;;)
  { int ce;

    for ( ; state->current; state->current = state->current->next )
    { if ( state->current->references )
      { if ( !PL_unify_atom(r, state->current->name) )
	{ PL_free(state);
	  return FALSE;				/* error */
	}
	state->current = state->current->next;
	PL_retry_address(state);
      }
    }

    if ( (ce = ++state->current_entry) < state->rdb->hash.bucket_count )
    { state->current = state->rdb->hash.blocks[MSB(ce)][ce];
    } else
    { PL_free(state);
      return FALSE;
    }
  }
}


#ifdef O_DEBUG
#define RDF_LOOKUP_RESOURCE
static foreign_t
rdf_lookup_resource(term_t r)
{ rdf_db *db = rdf_current_db();
  atom_t a;

  if ( !PL_get_atom_ex(r, &a) )
    return FALSE;

  lookup_resource(&db->resources, a);

  return TRUE;
}
#endif

#define MKFUNCTOR(n, a) \
	FUNCTOR_ ## n ## a = PL_new_functor(PL_new_atom(#n), a)
#define NDET PL_FA_NONDETERMINISTIC

int
register_resource_predicates(void)
{ MKFUNCTOR(literal, 1);

  PL_register_foreign("rdf_resource",        1, rdf_resource,        NDET);
#ifdef RDF_LOOKUP_RESOURCE
  PL_register_foreign("rdf_lookup_resource", 1, rdf_lookup_resource, 0);
#endif

  return TRUE;
}