File: pl-gvar.c

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/*  $Id$

    Part of SWI-Prolog

    Author:        Jan Wielemaker and Anjo Anjewierden
    E-mail:        J.Wielemaker@cs.vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 1985-2009, University of Amsterdam

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

/*#define O_DEBUG 1*/
#include "pl-incl.h"
#ifdef O_GVAR


		 /*******************************
		 * NON-BACKTRACKABLE GLOBAL VARS*
		 *******************************/

void
freezeGlobal(ARG1_LD)
{ LD->frozen_bar = LD->mark_bar = gTop;
  DEBUG(2, Sdprintf("*** frozen bar to %p at freezeGlobal()\n",
		    LD->frozen_bar));
}


void
destroyGlobalVars()
{ GET_LD

  if ( LD->gvar.nb_vars )
  { destroyHTable(LD->gvar.nb_vars);
    LD->gvar.nb_vars = NULL;
  }

  LD->gvar.grefs = 0;
  LD->frozen_bar = NULL;
}


static void
free_nb_linkval_symbol(Symbol s)
{ word w = (word)s->value;

  if ( isAtom(w) )
    PL_unregister_atom(w);
  else if ( storage(w) == STG_GLOBAL )
  { GET_LD
    LD->gvar.grefs--;
  }

  PL_unregister_atom((atom_t)s->name);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Assign  a  global  variable.  For    backtrackable   variables  we  need
TrailAssignment(), but we can only call that  on addresses on the global
stack. Therefore we must make  a  reference   to  the  real value if the
variable is not already a reference.

SHIFT-SAFE: TrailAssignment() takes at most g+t=1+2.  One more Trail and
	    2 more allocGlobal(1) makes g+t<3+3
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int
setval(term_t var, term_t value, int backtrackable ARG_LD)
{ atom_t name;
  Word p;
  word w, old;
  Symbol s;

  if ( !PL_get_atom_ex(var, &name) )
    fail;

  if ( !LD->gvar.nb_vars )
  { LD->gvar.nb_vars = newHTable(32|TABLE_UNLOCKED);
    LD->gvar.nb_vars->free_symbol = free_nb_linkval_symbol;
  }

  if ( !hasGlobalSpace(3) )		/* also ensures trail for */
  { int rc;				/* TrailAssignment() */

    if ( (rc=ensureGlobalSpace(3, ALLOW_GC)) != TRUE )
      return raiseStackOverflow(rc);
  }

  p = valTermRef(value);
  deRef(p);
  w = *p;

  if ( canBind(w) )
  { if ( onStackArea(local, p) )
    { Word p2 = allocGlobal(1);

      setVar(*p2);
      w = *p = makeRef(p2);
      LTrail(p);
    } else
    { w = makeRef(p);
    }
  }

  if ( !(s=lookupHTable(LD->gvar.nb_vars, (void*)name)) )
  { s = addHTable(LD->gvar.nb_vars, (void*)name, (void*)ATOM_nil);
    PL_register_atom(name);
    PL_register_atom(ATOM_nil);
  }
  assert(s);

  old = (word)s->value;
  if ( w == old )
    succeed;
  if ( isAtom(old) )
    PL_unregister_atom(old);

  if ( backtrackable )
  { Word p;

    if ( isRef(old) )
    { p = unRef(old);
    } else
    { p = allocGlobal(1);
      *p = old;
      freezeGlobal(PASS_LD1);		/* The value location must be */
      if ( storage(old) != STG_GLOBAL )	/* preserved */
	LD->gvar.grefs++;
      s->value = (void*)makeRefG(p);
    }

    TrailAssignment(p);
    *p = w;
  } else
  { if ( storage(old) == STG_GLOBAL )
      LD->gvar.grefs--;

    s->value = (void *)w;

    if ( storage(w) == STG_GLOBAL )
    { freezeGlobal(PASS_LD1);
      LD->gvar.grefs++;
    } else if ( isAtom(w) )
      PL_register_atom(w);
  }

  succeed;
}


typedef enum
{ gvar_fail,
  gvar_retry,
  gvar_error
} gvar_action;


static gvar_action
auto_define_gvar(atom_t name)
{ GET_LD
  static predicate_t pred;
  fid_t fid;
  term_t av;
  gvar_action rc = gvar_error;

  if ( !pred )
    pred = PL_predicate("exception", 3, "user");

  if ( !(fid = PL_open_foreign_frame()) )
    return gvar_error;
  av = PL_new_term_refs(3);
  PL_put_atom(av+0, ATOM_undefined_global_variable);
  PL_put_atom(av+1, name);

  if ( PL_call_predicate(NULL, PL_Q_PASS_EXCEPTION, pred, av) )
  { atom_t action;			/* retry, error, fail */

    if ( (rc=PL_get_atom_ex(av+2, &action)) )
    { if ( action == ATOM_retry )
	rc = gvar_retry;
      else if ( action == ATOM_fail )
	rc = gvar_fail;
    }
  }


  PL_close_foreign_frame(fid);

  return rc;
}


/* gvar_value__LD() is a quick and dirty way to get a global variable.
   It is used to get '$variable_names' for compiler warnings.

   Note that this function does *not* call auto_define_gvar().  This
   is on purpose because we cannot call Prolog from the compiler and
   there is no need for this hook for this variable.  Be careful to
   fix this if this function is to be used for other purposes.
*/

int
gvar_value__LD(atom_t name, Word p ARG_LD)
{ if ( LD->gvar.nb_vars )
  { Symbol s = lookupHTable(LD->gvar.nb_vars, (void*)name);

    if ( s )
    { *p = (word)s->value;
      return TRUE;
    }
  }

  return FALSE;
}


static int
getval(term_t var, term_t value, int raise_error ARG_LD)
{ atom_t name;
  int i;

  if ( !PL_get_atom_ex(var, &name) )
    fail;
  if ( !hasGlobalSpace(0) )
  { int rc;

    if ( (rc=ensureGlobalSpace(0, ALLOW_GC)) != TRUE )
      return raiseStackOverflow(rc);
  }


  for(i=0; i<2; i++)
  { if ( LD->gvar.nb_vars )
    { Symbol s = lookupHTable(LD->gvar.nb_vars, (void*)name);

      if ( s )
      { term_t tmp = PL_new_term_ref();
	word w = (word)s->value;

	*valTermRef(tmp) = w;
	return PL_unify(value, tmp);
      }
    }

    switch(auto_define_gvar(name))
    { case gvar_fail:
	fail;
      case gvar_retry:
	continue;
      case gvar_error:
	if ( exception_term )
	  fail;				/* error from handler */
        goto error;
    }
  }

error:
  if ( raise_error )
    return PL_error(NULL, 0, NULL, ERR_EXISTENCE,
		    ATOM_variable, var);
  else
    return FALSE;
}


static
PRED_IMPL("nb_linkval", 2, nb_linkval, 0)
{ PRED_LD

  return setval(A1, A2, FALSE PASS_LD);
}


static
PRED_IMPL("nb_getval", 2, nb_getval, 0)
{ PRED_LD

  return getval(A1, A2, TRUE PASS_LD);
}


static
PRED_IMPL("b_setval", 2, b_setval, 0)
{ PRED_LD

  return setval(A1, A2, TRUE PASS_LD);
}

static
PRED_IMPL("b_getval", 2, b_getval, 0)
{ PRED_LD

  return getval(A1, A2, TRUE PASS_LD);
}


static
PRED_IMPL("nb_delete", 1, nb_delete, 0)
{ PRED_LD
  atom_t name;

  if ( !PL_get_atom_ex(A1, &name) )
    fail;

  if ( LD->gvar.nb_vars )
  { Symbol s = lookupHTable(LD->gvar.nb_vars, (void*)name);

    if ( s )
    { free_nb_linkval_symbol(s);
      deleteSymbolHTable(LD->gvar.nb_vars, s);
    }
  }

  succeed;
}


static
PRED_IMPL("nb_current", 2, nb_current, PL_FA_NONDETERMINISTIC)
{ PRED_LD
  TableEnum e;
  Symbol s;
  fid_t fid;

  switch( CTX_CNTRL )
  { case FRG_FIRST_CALL:
      if ( PL_is_atom(A1) )
	return getval(A1, A2, FALSE PASS_LD);
      if ( !PL_is_variable(A1) )
	return PL_type_error("atom", A1);
      if ( LD->gvar.nb_vars )
      { e = newTableEnum(LD->gvar.nb_vars);
	break;
      } else
      { fail;
      }
    case FRG_REDO:
      e =  CTX_PTR;
      break;
    case FRG_CUTTED:
      e =  CTX_PTR;
      freeTableEnum(e);
      succeed;
    default:
      assert(0);
      fail;
  }

  if ( !(fid = PL_open_foreign_frame()) )
  { freeTableEnum(e);
    return FALSE;
  }
  while( (s=advanceTableEnum(e)) )
  { atom_t name = (atom_t)s->name;
    word   val = (word)s->value;

    if ( PL_unify_atom(A1, name) &&
	 unify_ptrs(valTermRef(A2), &val, 0 PASS_LD) )
    { PL_close_foreign_frame(fid);
      ForeignRedoPtr(e);
    } else
    { PL_rewind_foreign_frame(fid);
    }
  }
  PL_close_foreign_frame(fid);

  freeTableEnum(e);
  fail;
}


		 /*******************************
		 *	    REGISTRATION	*
		 *******************************/

BeginPredDefs(gvar)
  PRED_DEF("b_setval",   2, b_setval,   0)
  PRED_DEF("b_getval",   2, b_getval,   0)
  PRED_DEF("nb_linkval", 2, nb_linkval, 0)
  PRED_DEF("nb_getval",  2, nb_getval,  0)
  PRED_DEF("nb_current", 2, nb_current, PL_FA_NONDETERMINISTIC)
  PRED_DEF("nb_delete",  1, nb_delete,  0)
EndPredDefs

#endif /*O_ATTVAR*/