/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  1985-2017, University of Amsterdam
                              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.
*/

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

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
General  handling  of  procedures:  creation;  adding/removing  clauses;
finding source files, etc.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

#undef LD
#define LD LOCAL_LD

static void	resetProcedure(Procedure proc, bool isnew);
static atom_t	autoLoader(Definition def);
static Procedure visibleProcedure(functor_t f, Module m ARG_LD);
static void	freeClauseRef(ClauseRef cref);
static int	setDynamicDefinition_unlocked(Definition def, bool isdyn);
static void	registerDirtyDefinition(Definition def ARG_LD);
static void	unregisterDirtyDefinition(Definition def);
static size_t	clause_count_in_dirty_predicates(ARG1_LD);

/* Enforcing this limit demands we propagate NULL from lookupProcedure()
   through the whole system.  This is not done
*/
#define O_PROGLIMIT_INCL_PRED 0
#define SIZEOF_PROC (sizeof(struct procedure) + sizeof(struct definition))

Procedure
lookupProcedure(functor_t f, Module m)
{ GET_LD
  Procedure proc, oproc;
  Definition def;

  if ( (proc = lookupHTable(m->procedures, (void *)f)) )
  { DEBUG(MSG_PROC, Sdprintf("lookupProcedure(%s) --> %s\n",
			     PL_atom_chars(m->name),
			     procedureName(proc)));
    return proc;
  }

#if O_PROGLIMIT_INCL_PRED
  if ( m->code_limit &&
       m->code_size + SIZEOF_PROC > m->code_limit )
  { PL_error(NULL, 0, NULL, ERR_RESOURCE, ATOM_program_space);
    return NULL;
  }
#endif

  proc = (Procedure)  allocHeapOrHalt(sizeof(struct procedure));
  def  = (Definition) allocHeapOrHalt(sizeof(struct definition));
  proc->definition = def;
  proc->flags      = 0;
  proc->source_no  = 0;

  memset(def, 0, sizeof(*def));
  def->functor = valueFunctor(f);
  def->module  = m;
  def->shared  = 1;
  if ( def->functor->arity > 0 )
  { def->impl.any.args = allocHeapOrHalt(sizeof(arg_info)*def->functor->arity);
    memset(def->impl.any.args, 0, sizeof(arg_info)*def->functor->arity);
  } else
  { def->impl.any.args = NULL;
  }
  resetProcedure(proc, TRUE);

  DEBUG(MSG_PROC_COUNT, Sdprintf("Created %s\n", procedureName(proc)));
  ATOMIC_INC(&GD->statistics.predicates);
  ATOMIC_ADD(&m->code_size, SIZEOF_PROC);

  if ( (oproc=addHTable(m->procedures, (void *)f, proc)) == proc )
  { return proc;
  } else
  { unallocProcedure(proc);
    return oproc;
  }
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
lingerDefinition() deals with (undefined) definitions  that are replaced
due to importing. These definitions can be   in  use with other threads.
This needs be be improved, possibly using a technique similar to the RDF
database. For now, we merely collect them in  a single place, so we know
what is going on. In addition, we can collect lingering definitions when
destroying a module, resulting in leak-free temporary modules.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

void
lingerDefinition(Definition def)
{ ListCell c = allocHeapOrHalt(sizeof(*c));
  Module m = def->module;
  ListCell o;

  c->value     = def;
  do
  { o            = m->lingering;
    c->next      = o;
  } while( !COMPARE_AND_SWAP(&m->lingering, o, c) );

  DEBUG(MSG_PROC_COUNT, Sdprintf("Linger %s\n", predicateName(def)));
  ATOMIC_SUB(&m->code_size, sizeof(*def));
  ATOMIC_DEC(&GD->statistics.predicates);

  /*GC_LINGER(def);*/
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
destroyDefinition() is called to destroy predicates from destroyModule()
as well as destroying thread-local  instantiations   while  a  thread is
being terminated. In both  cases  is  the   predicate  known  to  be not
referenced.

However, we cannot simply discard  everything   as  the predicate may be
involved in clause-GC. Therefore we need to leave the entire cleaning to
clause-GC. This is somewhat slower than  the   old  way around. The good
news is the it works towards more   general garbage collection for code,
e.g., eventually we may be able  to   destroy  modules even if we cannot
guarantee they are not in use.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

void
destroyDefinition(Definition def)
{ ATOMIC_DEC(&GD->statistics.predicates);
  ATOMIC_SUB(&def->module->code_size, sizeof(*def));

  freeCodesDefinition(def, FALSE);

  if ( false(def, P_FOREIGN|P_THREAD_LOCAL) )	/* normal Prolog predicate */
  { freeHeap(def->impl.any.args, sizeof(arg_info)*def->functor->arity);
    removeClausesPredicate(def, 0, FALSE);
    DEBUG(MSG_CGC_PRED,
	  Sdprintf("destroyDefinition(%s)\n", predicateName(def)));
    if ( true(def, P_DIRTYREG) )
    { DEBUG(MSG_PROC_COUNT, Sdprintf("Erased %s\n", predicateName(def)));
      def->module = NULL;
      set(def, P_ERASED);
    } else
    { DEBUG(MSG_PROC_COUNT, Sdprintf("Unalloc %s\n", predicateName(def)));
      freeHeap(def, sizeof(*def));
    }
  } else					/* foreign and thread-local */
  { DEBUG(MSG_PROC_COUNT, Sdprintf("Unalloc foreign/thread-local: %s\n",
				   predicateName(def)));
    if ( true(def, P_DIRTYREG) )
    { DEBUG(0, if ( GD->cleaning == CLN_NORMAL )
	         Sdprintf("Destroying dirty predicate: %s\n",
			  predicateName(def)));
      unregisterDirtyDefinition(def);
    }

#ifdef O_PLMT
    if ( true(def, P_THREAD_LOCAL) )
      free_ldef_vector(def->impl.local);
#endif

    freeHeap(def, sizeof(*def));
  }
}


void
unallocProcedure(Procedure proc)
{ Definition def = proc->definition;
  Module m = def->module;

  if ( unshareDefinition(def) == 0 )
  { DEBUG(MSG_PROC, Sdprintf("Reclaiming %s\n", predicateName(def)));
    destroyDefinition(def);
  }
  freeHeap(proc, sizeof(*proc));
  if ( m )
    ATOMIC_SUB(&m->code_size, sizeof(*proc));
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Add (import) a definition to a module.  Used by loadImport() for loading
states and QLF files. Must be merged with import/1.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

int
importDefinitionModule(Module m, Definition def, int flags)
{ GET_LD
  functor_t functor = def->functor->functor;
  Procedure proc;
  int rc = TRUE;

  LOCKMODULE(m);
  if ( (proc = lookupHTable(m->procedures, (void *)functor)) )
  { if ( proc->definition != def )
    { if ( !isDefinedProcedure(proc) )
      { Definition odef = proc->definition;

	shareDefinition(def);
	proc->definition = def;
	if ( unshareDefinition(odef) == 0 )
	  lingerDefinition(odef);
      } else
      { if ( !(flags&PROC_WEAK) )
	  rc = warning("Failed to import %s into %s",
		       predicateName(def), PL_atom_chars(m->name));
      }
    }
  } else
  { proc = (Procedure) allocHeapOrHalt(sizeof(struct procedure));
    proc->definition = def;
    proc->flags      = flags;
    proc->source_no  = 0;
    addNewHTable(m->procedures, (void *)functor, proc);
    shareDefinition(def);
  }
  UNLOCKMODULE(m);

  return rc;
}



/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
resetProcedure() is called  by  lookupProcedure()   for  new  ones,  and
abolishProcedure() by abolish/2.

There are two cases where a  complete  reset   is  safe:  if  this is an
unreferenced dynamic predicate and if this is   a  predicate that has no
clause-list. Such predicates can't be active  and can't become active as
that requires clauses which, even under  MT,   can  only  be added after
locking the L_PREDICATE mutex.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static void
resetProcedure(Procedure proc, bool isnew)
{ Definition def = proc->definition;

  if ( (true(def, P_DYNAMIC) /*&& def->references == 0*/) ||
       !def->impl.any.defined )
    isnew = TRUE;

  def->flags ^= def->flags & ~(SPY_ME|P_DIRTYREG);
  if ( stringAtom(def->functor->name)[0] != '$' )
    set(def, TRACE_ME);
  def->impl.clauses.number_of_clauses = 0;

  if ( isnew )
  { deleteIndexes(&def->impl.clauses, TRUE);
    freeCodesDefinition(def, FALSE);
  } else
    freeCodesDefinition(def, TRUE);	/* carefully sets to S_VIRGIN */
}


Procedure
isCurrentProcedure__LD(functor_t f, Module m ARG_LD)
{ return lookupHTable(m->procedures, (void *)f);
}


ClauseRef
hasClausesDefinition(Definition def)
{ if ( false(def, P_FOREIGN|P_THREAD_LOCAL) &&
       def->impl.clauses.first_clause )
  { GET_LD
    ClauseRef c;
    gen_t generation = global_generation();

    acquire_def(def);
    for(c = def->impl.clauses.first_clause; c; c = c->next)
    { Clause cl = c->value.clause;

      if ( visibleClauseCNT(cl, generation) )
	break;
    }
    release_def(def);

    return c;
  }

  return NULL;
}


bool
isDefinedProcedure(Procedure proc)
{ Definition def = proc->definition;

  if ( true(def, PROC_DEFINED) )
    succeed;

  return hasClausesDefinition(def) ? TRUE : FALSE;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Find a procedure for defining it.  Here   we check whether the procedure
to be defined is a system predicate.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

Procedure
isStaticSystemProcedure(functor_t fd)
{ GET_LD
  Procedure proc;

  if ( !SYSTEM_MODE &&
       MODULE_system &&
       (proc=isCurrentProcedure(fd, MODULE_system)) &&
       true(proc->definition, P_LOCKED) &&
       false(proc->definition, P_DYNAMIC) )
    return proc;

  return NULL;
}


int
checkModifySystemProc(functor_t fd)
{ Procedure proc;

  if ( (proc = isStaticSystemProcedure(fd)) &&
       true(proc->definition, P_ISO) )
    return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);

  succeed;
}


int
overruleImportedProcedure(Procedure proc, Module target)
{ GET_LD
  Definition def = getProcDefinition(proc);

  assert(def->module != target);	/* e.g., imported */
  if ( true(def->module, M_SYSTEM) )
  { return PL_error(NULL, 0, NULL, ERR_PERMISSION_PROC,
		    ATOM_redefine, ATOM_built_in_procedure, proc);
  } else
  { if ( proc->flags & PROC_WEAK )
    { if ( truePrologFlag(PLFLAG_WARN_OVERRIDE_IMPLICIT_IMPORT) )
      { term_t pi;

	if ( !(pi=PL_new_term_ref()) ||
	     !PL_unify_predicate(pi, proc, GP_NAMEARITY) ||
	     !printMessage(ATOM_warning,
			   PL_FUNCTOR_CHARS, "ignored_weak_import", 2,
			     PL_ATOM, target->name,
			     PL_TERM, pi) )
	  return FALSE;
      }

      abolishProcedure(proc, target);
      return TRUE;
    }
  }

  return PL_error(NULL, 0, NULL, ERR_PERMISSION_PROC,
		  ATOM_redefine, ATOM_imported_procedure, proc);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
lookupProcedureToDefine() locates the proc for  a   functor  in a module
with the aim of providing a  definition   for  this  procedure, e.g., to
declare it as a meta-predicate, dynamic, etc.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

Procedure
lookupProcedureToDefine(functor_t def, Module m)
{ GET_LD
  Procedure proc;

  if ( (proc = isCurrentProcedure(def, m)) )
  { Definition def = getProcDefinition(proc);

    if ( def->module != m )
    { if ( !overruleImportedProcedure(proc, m) )
	return NULL;
    }

    return proc;
  }

  if ( checkModifySystemProc(def) )
    return lookupProcedure(def, m);

  return NULL;
}


Procedure
getDefinitionProc(Definition def)
{ GET_LD
  Procedure proc = isCurrentProcedure(def->functor->functor, def->module);
  assert(proc);
  return proc;
}


void
shareDefinition(Definition def)
{ int shared = ATOMIC_INC(&def->shared);
  assert(shared > 0);
  (void)shared;
}


int
unshareDefinition(Definition def)
{ return ATOMIC_DEC(&def->shared);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
get_functor() translates term  of  the   format  +Name/+Arity  into  the
internal functor represenation. It fails and  raises an exception on the
various possible format or representation errors.  ISO compliant.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int
get_arity(term_t t, int extra, int maxarity, int *arity)
{ int a;

  if ( !PL_get_integer_ex(t, &a) )
    fail;
  if ( a < 0 )
    return PL_error(NULL, 0, NULL, ERR_DOMAIN,
		    ATOM_not_less_than_zero, t);
  a += extra;
  if ( maxarity >= 0 && a > maxarity )
  { char buf[100];

    Ssprintf(buf, "limit is %d, request = %d", maxarity, a);

    return PL_error(NULL, 0, buf,
		    ERR_REPRESENTATION, ATOM_max_arity);
  }

  *arity = a;

  return TRUE;
}


int
get_functor(term_t descr, functor_t *fdef, Module *m, term_t h, int how)
{ GET_LD
  term_t head;
  int dcgpi=FALSE;

  if ( !(how&GP_NOT_QUALIFIED) )
  { head = PL_new_term_ref();
    if ( !PL_strip_module(descr, m, head) )
      return FALSE;
  } else
  { head = descr;
  }

  if ( PL_is_functor(head, FUNCTOR_divide2) ||
       (dcgpi=PL_is_functor(head, FUNCTOR_gdiv2)) )
  { term_t a = PL_new_term_ref();
    atom_t name;
    int arity = 0;

    _PL_get_arg(1, head, a);
    if ( !PL_get_atom_ex(a, &name) )
      fail;
    _PL_get_arg(2, head, a);
    if ( !get_arity(a,
		    (dcgpi ? 2 : 0),
		    (how&GF_PROCEDURE) ? MAXARITY : -1,
		    &arity ) )
      fail;
    *fdef = PL_new_functor(name, arity);
    if ( h )
      PL_put_term(h, head);

    succeed;
  } else if ( !(how&GF_NAMEARITY) && PL_get_functor(head, fdef) )
  { if ( h )
      PL_put_term(h, head);

    succeed;
  } else
  { if ( how & GP_TYPE_QUIET )
      fail;
    else
      return PL_error(NULL, 0, NULL, ERR_TYPE,
		      ATOM_predicate_indicator, head);
  }
}


int
get_head_functor(term_t head, functor_t *fdef, int how ARG_LD)
{ FunctorDef fd;

  if ( !PL_get_functor(head, fdef) )
  { if ( how&GP_TYPE_QUIET )
      fail;
    else
      return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_callable, head);
  }

  fd = valueFunctor(*fdef);

  if ( fd->arity > MAXARITY )
  { if ( how&GP_TYPE_QUIET )
    { fail;
    } else
    { char buf[100];

      Ssprintf(buf, "limit is %d, request = %d", MAXARITY, fd->arity);

      return PL_error(NULL, 0, buf,
		      ERR_REPRESENTATION, ATOM_max_arity);
    }
  }

  if ( !isCallableAtom(fd->name) )
  { if ( how&GP_TYPE_QUIET )
    { fail;
    } else
    { return PL_error(NULL, 0, NULL,
		      ERR_TYPE, ATOM_callable, head);
    }
  }

  succeed;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Get the specified procedure from a   Prolog  argument.  This argument is
either a head or a term of the form module:head.  If `create' is TRUE, a
procedure is created in the module.  Otherwise, the system traverses the
module-inheritance chain to find the existing procedure.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static Module
get_module(atom_t mname, int how ARG_LD)
{ if ( mname )
  { switch(how&GP_HOW_MASK)
    { case GP_CREATE:
      case GP_DEFINE:
	return lookupModule(mname);
      case GP_FIND:
      case GP_FINDHERE:
      case GP_RESOLVE:
      { Module m;
	if ( (m=isCurrentModule(mname)) )
	  return m;
	return MODULE_user;
      }
    }
  }

  return (environment_frame ? contextModule(environment_frame)
			    : MODULE_user);
}


int
get_procedure(term_t descr, Procedure *proc, term_t h, int how)
{ GET_LD
  atom_t mname = 0;
  Module m = NULL;
  functor_t fdef;
  Procedure p;

  if ( (how&GP_NAMEARITY) )
  { if ( !get_functor(descr, &fdef, &m, h,
		      GF_PROCEDURE|(how&GP_TYPE_QUIET)) )
      fail;
  } else
  { term_t head = PL_new_term_ref();
    Word p;

    if ( !(p=stripModuleName(valTermRef(descr), &mname PASS_LD)) )
      return FALSE;
    *valTermRef(head) = linkVal(p);

    if ( !(m = get_module(mname, how PASS_LD)) )
      return FALSE;

    if ( h )
      PL_put_term(h, head);

    if ( !get_head_functor(head, &fdef, how PASS_LD) )
      fail;
  }

  switch( how & GP_HOW_MASK )
  { case GP_CREATE:
      *proc = lookupBodyProcedure(fdef, m);
      break;
    case GP_FINDHERE:
      if ( (p = isCurrentProcedure(fdef, m)) )
      { *proc = p;
        break;
      }
      goto notfound;
    case GP_FIND:
      if ( (p = visibleProcedure(fdef, m PASS_LD)) )
      { *proc = p;
        goto out;
      }
      goto notfound;
    case GP_DEFINE:
      if ( (p = lookupProcedureToDefine(fdef, m)) )
      { *proc = p;
        break;
      }
      fail;				/* permission error */
    case GP_RESOLVE:
      if ( (p = resolveProcedure(fdef, m)) )
      { *proc = p;
        break;
      }
      goto notfound;
    default:
      assert(0);
  }
out:
  succeed;

notfound:
  if ( (how & GP_EXISTENCE_ERROR) )
    return PL_error(NULL, 0, NULL, ERR_EXISTENCE, ATOM_procedure, descr);
  fail;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This function  implements  $c_current_predicate/2.   current_predicate/2
itself  is  written  in  Prolog, based on this function.  Having dynamic
linking from super modules and dynamic loading from the  libraries,  the
definition  of current predicate has become a difficult issue.  Normally
it is used for meta-programming and program analysis.  I think it should
succeed  for  each  predicate  that  can   be   called.    The   current
implementation  is VERY slow due to all Prolog overhead.  This should be
reconsidered and probably a large part of this function should be  moved
to C.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

word
pl_current_predicate(term_t name, term_t spec, control_t h)
{ GET_LD
  TableEnum e;
  atom_t n;
  functor_t f;
  Module m = (Module) NULL;
  Procedure proc;
  term_t functor = PL_new_term_ref();

  if ( ForeignControl(h) == FRG_CUTTED )
  { e = ForeignContextPtr(h);
    freeTableEnum(e);
    succeed;
  }

  if ( !PL_strip_module__LD(spec, &m, functor, SM_NOCREATE PASS_LD) )
    fail;

  if ( !PL_get_atom(name, &n) )
  { if ( PL_is_variable(name) )
      n = NULL_ATOM;
    else
      fail;
  }
  if ( !PL_get_functor(functor, &f) )
  { if ( PL_is_variable(functor) )
      f = 0;
    else
      fail;
  }

  if ( ForeignControl(h) == FRG_FIRST_CALL)
  { if ( f )
    { if ( (proc = isCurrentProcedure(f, m)) )
	return PL_unify_atom(name, nameFunctor(f));
      fail;
    }
    e = newTableEnum(m->procedures);
  } else
    e = ForeignContextPtr(h);

  while( advanceTableEnum(e, NULL, (void**)&proc) )
  { FunctorDef fdef;

    fdef = proc->definition->functor;

    if ( (n && n != fdef->name) ||
	 !PL_unify_atom(name, fdef->name) ||
	 !PL_unify_functor(functor, fdef->functor) )
      continue;

    ForeignRedoPtr(e);
  }

  freeTableEnum(e);
  fail;
}

		 /*******************************
		 *    ISO CURRENT-PREDICATE/1	*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Patterns: ?Name/?Arity
	  ?Module:(?Name/?Arity)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

typedef struct
{ functor_t	functor;		/* Functor we are looking for */
  atom_t	name;			/* Name of target pred */
  int		arity;			/* arity of target pred */
  Module	module;			/* Module to search in */
  Module	super;			/* Walking along super-chain */
  TableEnum	epred;			/* Predicate enumerator */
  TableEnum	emod;			/* Module enumerator */
} cur_enum;


static Procedure
visibleProcedure(functor_t f, Module m ARG_LD)
{ ListCell c;
  Procedure p;

  for(;;)
  { next:

    if ( (p = isCurrentProcedure(f, m)) && isDefinedProcedure(p) )
      return p;

    for(c=m->supers; c; c=c->next)
    { if ( c->next )
      { if ( (p=visibleProcedure(f, c->value PASS_LD)) )
	  return p;
      } else
      { m = c->value;
	goto next;
      }
    }

    return NULL;
  }
}


foreign_t
pl_current_predicate1(term_t spec, control_t ctx)
{ GET_LD
  cur_enum e0;
  cur_enum *e;
  int rval = FALSE;
  term_t mt = 0;			/* module-term */
  term_t nt = 0;			/* name-term */
  term_t at = 0;			/* arity-term */
  unsigned int aextra = 0;

  if ( ForeignControl(ctx) != FRG_CUTTED )
  { term_t pi = PL_copy_term_ref(spec);

    nt = PL_new_term_ref();
    at = PL_new_term_ref();

    while( PL_is_functor(pi, FUNCTOR_colon2) )
    { if ( !mt )
	mt = PL_new_term_ref();
      _PL_get_arg(1, pi, mt);
      _PL_get_arg(2, pi, pi);
    }

    if ( PL_is_functor(pi, FUNCTOR_divide2) )
    { _PL_get_arg(1, pi, nt);
      _PL_get_arg(2, pi, at);
    } else if ( PL_is_functor(pi, FUNCTOR_gdiv2) )
    { _PL_get_arg(1, pi, nt);
      _PL_get_arg(2, pi, at);
      aextra = 2;
    } else if ( PL_is_variable(pi) )
    { term_t a;

      if ( !(a=PL_new_term_ref()) ||
	   !PL_cons_functor(a, FUNCTOR_divide2, nt, at) ||
	   !PL_unify(pi, a) )
	return FALSE;			/* resource error */
    } else
      goto typeerror;
  }

  switch( ForeignControl(ctx) )
  { case FRG_FIRST_CALL:
    { e = &e0;
      memset(e, 0, sizeof(*e));

      if ( !PL_get_atom(nt, &e->name) )
      { if ( !PL_is_variable(nt) )
	  goto typeerror;
      }
      if ( PL_get_integer(at, &e->arity) )
      { if ( e->arity < 0 )
	  return PL_error(NULL, 0, NULL, ERR_DOMAIN,
			  ATOM_not_less_than_zero, at);

	e->arity += aextra;
      } else
      { if ( !PL_is_variable(at) )
	  goto typeerror;
	e->arity = -1;
      }

      if ( e->name && e->arity >= 0 )
	e->functor = PL_new_functor(e->name, e->arity);

      if ( mt )
      { atom_t mname;

	if ( PL_is_variable(mt) )
	{ Module m;
	  e->emod = newTableEnum(GD->tables.modules);

	  if ( advanceTableEnum(e->emod, NULL, (void**)&m) )
	    e->module = m;
	  else
	    fail;			/* no modules!? */
	} else if ( PL_get_atom_ex(mt, &mname) )
	{ e->module = isCurrentModule(mname);
	  if ( !e->module )
	    fail;
	} else
	{ fail;
	}
      } else
      { if ( environment_frame )
	  e->module = contextModule(environment_frame);
	else
	  e->module = MODULE_user;
	e->super = e->module;
      }

      if ( e->functor )
      { if ( !e->emod )			/* fully specified */
	  return (visibleProcedure(e->functor, e->module PASS_LD) != NULL);
      } else
      { e->epred = newTableEnum(e->module->procedures);
      }

      e = allocForeignState(sizeof(*e));
      *e = e0;
      break;
    }
    case FRG_REDO:
      e = ForeignContextPtr(ctx);
      break;
    case FRG_CUTTED:
    { e = ForeignContextPtr(ctx);
      rval = TRUE;
      goto clean;
    }
    default:
    { e = NULL;
      assert(0);
    }
  }

  for(;;)
  { if ( e->functor )			/* _M:foo/2 */
    { if ( visibleProcedure(e->functor, e->module PASS_LD) )
      { Module m;
	PL_unify_atom(mt, e->module->name);

	if ( advanceTableEnum(e->emod, NULL, (void**)&m) )
	{ e->module = m;
	  ForeignRedoPtr(e);
	} else
	{ rval = TRUE;
	  goto clean;
	}
      }
    } else
    { functor_t f;
      Procedure proc;
      while( advanceTableEnum(e->epred, (void**)&f, (void**)&proc) )
      { FunctorDef fd = valueFunctor(f);

	if ( (!e->name     || e->name == fd->name) &&
	     (e->arity < 0 || (unsigned int)e->arity == fd->arity) &&
	     fd->arity >= aextra &&
	     isDefinedProcedure(proc) )
	{ if ( mt )
	    PL_unify_atom(mt, e->module->name);
	  if ( !e->name )
	    PL_unify_atom(nt, fd->name);
	  if ( e->arity < 0 )
	    PL_unify_integer(at, fd->arity-aextra);

	  ForeignRedoPtr(e);
	}
      }
    }

    if ( e->emod )			/* enumerate all modules */
    { Module m;
      while( advanceTableEnum(e->emod, NULL, (void**)&m) )
      {
					/* skip hidden modules */
	if ( SYSTEM_MODE ||
	     m->name == ATOM_system ||
	     m->class != ATOM_system )
	  break;
      }
      if ( m )
	e->super = e->module = m;
      else
	break;
    } else if ( !e->functor && e->super && e->super->supers )
    { e->super = e->super->supers->value;	/* advance to user-modules */
					/* TBD: handle multiple supers */
    } else
      break;				/* finished all modules */

    if ( !e->functor )
    { freeTableEnum(e->epred);
      e->epred = newTableEnum(e->super->procedures);
    }
  }

clean:
  if ( e )
  { if ( e->epred )
      freeTableEnum(e->epred);
    if ( e->emod )
      freeTableEnum(e->emod);
    freeForeignState(e, sizeof(*e));
  }

  return rval;

typeerror:
  return PL_error(NULL, 0, NULL, ERR_TYPE,
		  ATOM_predicate_indicator, spec);
}


		 /*******************************
		 *	 CLAUSE REFERENCES	*
		 *******************************/

#ifdef O_DEBUG
static Table retracted_clauses = NULL;

static void
registerRetracted(Clause cl)
{ DEBUG(MSG_CGC_CREF_PL, Sdprintf("/**/ r(%p).\n", cl));
  DEBUG(MSG_CGC_CREF_TRACK,
	{ if ( !retracted_clauses )
	    retracted_clauses = newHTable(1024);
	  addNewHTable(retracted_clauses, cl, (void*)1);
	});
}

static void
reclaimRetracted(Clause cl)
{ DEBUG(MSG_CGC_CREF_TRACK,
	{ void *v = deleteHTable(retracted_clauses, cl);
	  if ( v != (void*)1 && GD->cleaning == CLN_NORMAL )
	  { Definition def = cl->predicate;
	    Sdprintf("reclaim not retracted from %s\n", predicateName(def));
	  }
	});
}

void
listNotReclaimed(void)
{ if ( retracted_clauses )
  { for_table(retracted_clauses, n, v,
	      { Clause cl = n;
		Definition def = cl->predicate;

		Sdprintf("%p from %s\n", cl, predicateName(def));
	      });
  }
}

#else

#define registerRetracted(cl) (void)0
#define reclaimRetracted(cl)  (void)0

#endif


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Clause references are used  to  link   clauses  from  the main predicate
clause list as well as from additional  indexes. They form a linked list
of clauses, indexed according to a  specific   key.  This key is deduced
from the first argument for  the  main   predicate  clause  list or from
alternative arguments for secondary clause lists.

Traversing a list of clause  references   traverses  the ->next pointer,
possibly matches the key and then looks into the associated ->clause for
the born/died generations. If a clause erased, cleanDefinition() removes
the  references  to  it  from  the  linked    lists  and  adds  them  to
GD->lingering_clauses, which uses d.gnext to   link them together rather
then ->next because ->next might be used by some other thread traversing
the clause chain.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

ClauseRef
newClauseRef(Clause clause, word key)
{ ClauseRef cref = allocHeapOrHalt(SIZEOF_CREF_CLAUSE);

  DEBUG(MSG_CGC_CREF_PL,
	Sdprintf("/**/ a(%p, %p, %d, '%s').\n",
		 cref, clause, clause->references,
		 predicateName(clause->predicate)));

  cref->next         = NULL;
  cref->d.key        = key;
  cref->value.clause = clause;
  ATOMIC_INC(&clause->references);

  return cref;
}


static void
freeClauseRef(ClauseRef cref)
{ Clause cl = cref->value.clause;

  DEBUG(MSG_CGC_CREF_PL,
	Sdprintf("/**/ d(%p, %p, %d).\n",
		 cref, cl, (int)cl->references));

  if ( ATOMIC_DEC(&cl->references) == 0 )
  { size_t size = sizeofClause(cl->code_size) + SIZEOF_CREF_CLAUSE;

    ATOMIC_SUB(&GD->clauses.erased_size, size);
    ATOMIC_DEC(&GD->clauses.erased);

    reclaimRetracted(cl);
    freeClause(cl);
  }

  freeHeap(cref, SIZEOF_CREF_CLAUSE);
}


void
lingerClauseRef(ClauseRef cref)
{ ClauseRef o;

  do
  { o = GD->clauses.lingering;
    cref->d.gnext = o;
  } while(!COMPARE_AND_SWAP(&GD->clauses.lingering, o, cref) );

  ATOMIC_INC(&GD->clauses.lingering_count);
}


static int activePredicate(const Definition *defs, const Definition def);

static void
gcClauseRefs(void)
{ ClauseRef cref;

  if ( !(cref = GD->clauses.lingering) ||
       !COMPARE_AND_SWAP(&GD->clauses.lingering, cref, NULL) )
    return;			/* no work or someone else doing it */
  GD->clauses.lingering_count = 0;

  if ( cref )
  { ClauseRef next;
    Definition *active_defs = predicates_in_use();
    int freed = 0;
    int kept = 0;

    for( ; cref; cref = next)
    { Definition def;

      next = cref->d.gnext;
      def = cref->value.clause->predicate;
      if ( !activePredicate(active_defs, def) )
      { freeClauseRef(cref);
	freed++;
      } else
      {	lingerClauseRef(cref);
	kept++;
      }
    }

    if ( active_defs )
      PL_free(active_defs);

    DEBUG(MSG_CGC_CREF, Sdprintf("GC clause references: freed %d, kept %d\n",
				 freed, kept));
  }
}

static int
activePredicate(const Definition *defs, const Definition def)
{ if ( defs )
  { for( ; *defs; defs++)
    { if ( *defs == def )
	return TRUE;
    }
  }

  return FALSE;
}

static void
setLastModifiedPredicate(Definition def, gen_t gen)
{ Module m = def->module;

  def->last_modified = gen;

#ifdef HAVE___SYNC_ADD_AND_FETCH_8
{ gen_t lmm;

  do
  { lmm = m->last_modified;
  } while ( lmm < gen &&
	    !COMPARE_AND_SWAP(&m->last_modified, lmm, gen) );
}
#else
  LOCKMODULE(m);
  if ( m->last_modified < gen )
    m->last_modified = gen;
  UNLOCKMODULE(m);
#endif
}


		 /*******************************
		 *	      ASSERT		*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Assert a clause to a procedure. Where askes to assert either at the head
or at the tail of the clause list.

The `where` argument is one of

  - CL_START (asserta)
  - CL_END   (assertz)
  - The clause reference before which the clause must be inserted.
    This is used by reconsult.

(*) This function updates the indexing information.  If we have a static
procedure, it deletes the supervisor. This is  probably a bit rough, but
deals with -for example- clauses for   term_expansion/2. After the first
definition this will be  called  and   an  S_TRUSTME  supervisor will be
installed, causing further clauses to have no effect.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

ClauseRef
assertProcedure(Procedure proc, Clause clause, ClauseRef where ARG_LD)
{ Definition def = getProcDefinition(proc);
  word key;
  ClauseRef cref;

  argKey(clause->codes, 0, &key);
  cref = newClauseRef(clause, key);

  LOCKDEF(def);
  acquire_def(def);
  if ( !def->impl.clauses.last_clause )
  { def->impl.clauses.first_clause = def->impl.clauses.last_clause = cref;
  } else if ( where == CL_START || where == def->impl.clauses.first_clause )
  { cref->next = def->impl.clauses.first_clause;
    def->impl.clauses.first_clause = cref;
  } else if ( where == CL_END )
  { ClauseRef last = def->impl.clauses.last_clause;

    last->next = cref;
    def->impl.clauses.last_clause = cref;
  } else				/* insert before */
  { ClauseRef cr;

    for(cr = def->impl.clauses.first_clause; cr; cr = cr->next)
    { if ( cr->next == where )
      { cref->next = where;
	cr->next = cref;
	break;
      }
    }
    assert(cr);
  }

  def->impl.clauses.number_of_clauses++;
  if ( false(clause, UNIT_CLAUSE) )
    def->impl.clauses.number_of_rules++;
  ATOMIC_INC(&GD->statistics.clauses);
#ifdef O_LOGICAL_UPDATE
  clause->generation.created = next_global_generation();
  clause->generation.erased  = GEN_MAX;	/* infinite */
  setLastModifiedPredicate(def, clause->generation.created);
#endif

  if ( false(def, P_DYNAMIC) )		/* see (*) above */
    freeCodesDefinition(def, TRUE);

  addClauseToIndexes(def, clause, where);
  release_def(def);
  DEBUG(CHK_SECURE, checkDefinition(def));
  UNLOCKDEF(def);

  return cref;
}

/*  Abolish a procedure.  Referenced  clauses  are   unlinked  and left
    dangling in the dark until the procedure referencing it deletes it.

    Since we have a foreign language interface we will allow to  abolish
    foreign  predicates  as  well.  Permission testing should be done by
    the caller.

 ** Sun Apr 17 16:18:50 1988  jan@swivax.UUCP (Jan Wielemaker)  */

bool
abolishProcedure(Procedure proc, Module module)
{ GET_LD
  Definition def = proc->definition;

  DEBUG(MSG_PROC, Sdprintf("abolishProcedure(%s)\n", predicateName(def)));

  startCritical;
  LOCKDEF(def);
  if ( def->module != module )		/* imported predicate; remove link */
  { Definition ndef	     = allocHeapOrHalt(sizeof(*ndef));

    memset(ndef, 0, sizeof(*ndef));
    ndef->functor            = def->functor; /* should be merged with */
    ndef->impl.any.args	     = allocHeapOrHalt(sizeof(*ndef->impl.any.args)*
					       def->functor->arity);
    ndef->module             = module;	     /* lookupProcedure()!! */
    ndef->codes		     = SUPERVISOR(virgin);
    proc->definition         = ndef;
    ATOMIC_INC(&GD->statistics.predicates);
    ATOMIC_ADD(&module->code_size, sizeof(*ndef));
    resetProcedure(proc, TRUE);
  } else if ( true(def, P_FOREIGN) )	/* foreign: make normal */
  { def->impl.clauses.first_clause = def->impl.clauses.last_clause = NULL;
    resetProcedure(proc, TRUE);
  } else if ( true(def, P_THREAD_LOCAL) )
  { UNLOCKDEF(def);
    if ( !endCritical )
      return FALSE;
    return PL_error(NULL, 0, NULL, ERR_PERMISSION_PROC,
		    ATOM_modify, ATOM_thread_local_procedure, proc);
  } else				/* normal Prolog procedure */
  { removeClausesPredicate(def, 0, FALSE);
    setDynamicDefinition_unlocked(def, FALSE);
    resetProcedure(proc, FALSE);
  }

  DEBUG(CHK_SECURE, checkDefinition(def));
  UNLOCKDEF(def);

  return endCritical;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Remove (mark for  deletion)  all  clauses   that  come  from  the  given
source-file or any sourcefile. Note   that thread-local predicates don't
have clauses from files, so we don't   need to bother. Returns number of
clauses that has been deleted.

MT: Caller must hold L_PREDICATE
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

size_t
removeClausesPredicate(Definition def, int sfindex, int fromfile)
{ GET_LD
  ClauseRef c;
  size_t deleted = 0;
  size_t memory = 0;
  gen_t update = global_generation()+1;

  if ( true(def, P_THREAD_LOCAL) )
    return 0;

  acquire_def(def);
  for(c = def->impl.clauses.first_clause; c; c = c->next)
  { Clause cl = c->value.clause;

    if ( (sfindex == 0 || sfindex == cl->owner_no) &&
	 (!fromfile || cl->line_no > 0) &&
	 false(cl, CL_ERASED) )
    { set(cl, CL_ERASED);
#ifdef O_LOGICAL_UPDATE
      cl->generation.erased = update;
#endif
      deleted++;
      memory += sizeofClause(cl->code_size) + SIZEOF_CREF_CLAUSE;
      def->impl.clauses.number_of_clauses--;
      def->impl.clauses.erased_clauses++;
      if ( false(cl, UNIT_CLAUSE) )
	def->impl.clauses.number_of_rules--;
      deleteActiveClauseFromIndexes(def, cl);
      registerRetracted(cl);
    }
  }
  release_def(def);

  if ( global_generation() < update )
    next_global_generation();

  if ( deleted )
  { ATOMIC_SUB(&def->module->code_size, memory);
    ATOMIC_ADD(&GD->clauses.erased_size, memory);
    ATOMIC_ADD(&GD->clauses.erased, deleted);

    registerDirtyDefinition(def PASS_LD);
    DEBUG(CHK_SECURE, checkDefinition(def));
  }

  return deleted;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Retract  a  clause  from  a  dynamic  procedure.  Called  from  erase/1,
retract/1 and retractall/1. Returns FALSE  if   the  clause  was already
retracted.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

int
retractClauseDefinition(Definition def, Clause clause)
{ GET_LD
  size_t size = sizeofClause(clause->code_size) + SIZEOF_CREF_CLAUSE;

  assert(true(def, P_DYNAMIC));

  LOCKDEF(def);
  if ( true(clause, CL_ERASED) )
  { UNLOCKDEF(def);
    return FALSE;
  }

  DEBUG(CHK_SECURE, checkDefinition(def));
  set(clause, CL_ERASED);
  deleteActiveClauseFromIndexes(def, clause); /* just updates "dirtyness" */
  def->impl.clauses.number_of_clauses--;
  def->impl.clauses.erased_clauses++;
  if ( false(clause, UNIT_CLAUSE) )
    def->impl.clauses.number_of_rules--;
#ifdef O_LOGICAL_UPDATE
  clause->generation.erased = next_global_generation();
  setLastModifiedPredicate(def, clause->generation.erased);
#endif
  DEBUG(CHK_SECURE, checkDefinition(def));
  UNLOCKDEF(def);

					/* update stats */
  registerRetracted(clause);
  ATOMIC_SUB(&def->module->code_size, size);
  ATOMIC_ADD(&GD->clauses.erased_size, size);
  ATOMIC_INC(&GD->clauses.erased);

  registerDirtyDefinition(def PASS_LD);

  return TRUE;
}


void
unallocClause(Clause c)
{ ATOMIC_SUB(&GD->statistics.codes, c->code_size);
  ATOMIC_DEC(&GD->statistics.clauses);

#ifdef ALLOC_DEBUG
#define ALLOC_FREE_MAGIC 0xFB
  size_t size = sizeofClause(c->code_size);
  memset(c, ALLOC_FREE_MAGIC, size);
#endif

  PL_free(c);
}


#ifdef O_DEBUG_ATOMGC
void
unregister_atom_clause(atom_t a)
{ PL_unregister_atom(a);
}

void
register_atom_clause(atom_t a)
{ PL_register_atom(a);
}
#endif

void
freeClause(Clause c)
{
#ifdef O_ATOMGC
#ifdef O_DEBUG_ATOMGC
  forAtomsInClause(c, unregister_atom_clause);
#else
  forAtomsInClause(c, PL_unregister_atom);
#endif
#endif

  if ( true(c, DBREF_CLAUSE) )		/* will be freed from symbol */
    set(c, DBREF_ERASED_CLAUSE);
  else
    unallocClause(c);
}


static int WUNUSED			/* FALSE if there was an error */
announceErasedClause(Clause clause)
{
#if O_DEBUGGER
  int rc;
  Definition def = clause->predicate;

  rc = clearBreakPointsClause(clause) >= 0;
  if ( PROCEDURE_event_hook1 &&
       def != PROCEDURE_event_hook1->definition )
    rc = callEventHook(PLEV_ERASED_CLAUSE, clause) && rc;

  return rc;
#endif

  return TRUE;
}


static void
freeLingeringDefinition(Definition def, DirtyDefInfo ddi)
{ gen_t gen = ddi->oldest_generation == GEN_MAX ? global_generation()
						: ddi->oldest_generation;
  free_lingering(&def->lingering, gen);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
cleanDefinition()
    This function has two tasks. If the predicate needs to be rehashed,
    this is done and all erased clauses from the predicate are returned
    as a linked list.

    We cannot delete the clauses immediately as the debugger requires a
    call-back and we have the L_PREDICATE mutex when running this code.

find_prev() finds the real  previous  clause.   The  not-locked  loop of
cleanDefinition() keep track of this, but  in the meanwhile the previous
may change due to an assert. Now that we are in the locked region we can
search for the real previous, using   the  one from cleanDefinition() as
the likely candidate.

The `ddi->oldest_generation` contains the latest  marked generation that
was found or GEN_MAX  if  the  predicate   is  not  active.  The `start`
generation contains the generation when pl_garbage_collect_clauses() was
started.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int	mustCleanDefinition(const Definition def);

static ClauseRef
find_prev(Definition def, ClauseRef prev, ClauseRef cref)
{ if ( (!prev && def->impl.clauses.first_clause == cref) ||
       ( prev && prev->next == cref) )
    return prev;

  DEBUG(MSG_PROC, Sdprintf("Fixing prev\n"));
  for(prev = def->impl.clauses.first_clause; prev; prev = prev->next)
  { if ( prev->next == cref )
      return prev;
  }

  assert(0);
  return NULL;
}



/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(*) This used to be acquire_def(def),  but announceErasedClause may call
Prolog, leading to nested acquired definition. This is not needed anyway
as the acquired definition is only  used   by  clause  GC, we are inside
clause GC and clause GC calls cannot run in parallel.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static size_t
cleanDefinition(Definition def, DirtyDefInfo ddi, gen_t start, int *rcp)
{ size_t removed = 0;
  gen_t marked = ddi->oldest_generation;
  gen_t active = start < marked ? start : marked;

  DEBUG(CHK_SECURE,
	LOCKDEF(def);
	checkDefinition(def);
        UNLOCKDEF(def));

  if ( mustCleanDefinition(def) )
  { ClauseRef cref, prev = NULL;
#if O_DEBUG
    int left = 0;
#endif

    assert(GD->clauses.cgc_active);		/* See (*) */
    for(cref = def->impl.clauses.first_clause;
	cref && def->impl.clauses.erased_clauses;
	cref=cref->next)
    { Clause cl = cref->value.clause;

      if ( true(cl, CL_ERASED) && cl->generation.erased < active )
      { if ( !announceErasedClause(cl) )
	  *rcp = FALSE;

	LOCKDEF(def);
	prev = find_prev(def, prev, cref);
	if ( !prev )
	{ def->impl.clauses.first_clause = cref->next;
	  if ( !cref->next )
	    def->impl.clauses.last_clause = NULL;
	} else
	{ prev->next = cref->next;
	  if ( cref->next == NULL)
	    def->impl.clauses.last_clause = prev;
	}
	removed++;
	def->impl.clauses.erased_clauses--;
	UNLOCKDEF(def);

	lingerClauseRef(cref);
      } else
      { prev = cref;
	DEBUG(MSG_PROC, left++);
      }
    }
    if ( removed )
    { LOCKDEF(def);
      cleanClauseIndexes(def, &def->impl.clauses, active);
      UNLOCKDEF(def);
    }
    freeLingeringDefinition(def, ddi);

    DEBUG(CHK_SECURE,
	  LOCKDEF(def);
	  checkDefinition(def);
	  UNLOCKDEF(def));

    DEBUG(MSG_PROC,
	  Sdprintf("cleanDefinition(%s): removed %d, left %d, erased %d\n",
		   predicateName(def), removed, left,
		   def->impl.clauses.erased_clauses));
  }

  return removed;
}


static int
mustCleanDefinition(const Definition def)
{ return ( def->impl.clauses.erased_clauses > 0 );
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Finalize a reloaded predicate. This (nearly)   atomically  makes the new
definition visible.

(*) Updating the generation to one in the future and incrementing at the
end makes the transaction truely atomic.   In the current implementation
though, another thread may increment the  generation as well, making our
changes not entirely atomic. The lock-free retry mechanism won't work to
fix this. Only a true lock for modifying the generation can fix this.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

void
reconsultFinalizePredicate(sf_reload *rl, Definition def, p_reload *r ARG_LD)
{ if ( true(r, P_MODIFIED) )
  { ClauseRef cref;
    gen_t update   = global_generation()+1;	/* see (*) */
    size_t deleted = 0;
    size_t added   = 0;
    size_t memory  = 0;

    acquire_def(def);
    for(cref = def->impl.clauses.first_clause; cref; cref=cref->next)
    { Clause cl = cref->value.clause;

      if ( cl->generation.erased == rl->reload_gen && false(cl, CL_ERASED) )
      { set(cl, CL_ERASED);
	cl->generation.erased = update;
	deleted++;
	memory += sizeofClause(cl->code_size) + SIZEOF_CREF_CLAUSE;
	def->impl.clauses.number_of_clauses--;
	def->impl.clauses.erased_clauses++;
	if ( false(cl, UNIT_CLAUSE) )
	  def->impl.clauses.number_of_rules--;
	if ( true(def, P_DYNAMIC) )
	  deleteActiveClauseFromIndexes(def, cl);
	registerRetracted(cl);
      } else if ( cl->generation.created == rl->reload_gen )
      { cl->generation.created = update;
	added++;
      }
    }
    release_def(def);

    if ( global_generation() < update )	/* see (*) */
      next_global_generation();

    DEBUG(MSG_RECONSULT_CLAUSE,
	  Sdprintf("%s: added %ld, deleted %ld clauses "
		   "at gen=%ld, GD->gen = %lld\n",
		   predicateName(def), (long)added, (long)deleted,
		   (long)update, (int64_t)global_generation()));

    if ( added || deleted )
      setLastModifiedPredicate(def, update);

    if ( deleted )
    { ATOMIC_SUB(&def->module->code_size, memory);
      ATOMIC_ADD(&GD->clauses.erased_size, memory);
      ATOMIC_ADD(&GD->clauses.erased, deleted);

      registerDirtyDefinition(def PASS_LD);
    }

    DEBUG(CHK_SECURE, checkDefinition(def));
  }
}


		 /*******************************
		 *	  META PREDICATE	*
		 *******************************/

/** meta_predicate :HeadList is det.

Declaration for meta-predicates. The  declaration   fills  the meta_info
field of a definition as well  as   the  P_META and P_TRANSPARENT flags.
P_META indicates that meta_info is   valid. P_TRANSPARENT indicates that
the declaration contains at least one meta-argument (: or 0..9).

@param HeadList	Comma separated list of predicates heads, where each
		predicate head has arguments 0..9, :,+,-,?
*/

int
isTransparentMetamask(Definition def, arg_info *args)
{ size_t i, arity = def->functor->arity;
  int transparent = FALSE;

  for(i=0; i<arity && !transparent; i++)
  { int ma = args[i].meta;
    if ( MA_NEEDS_TRANSPARENT(ma) )
      transparent = TRUE;
  }

  return transparent;
}


void
setMetapredicateMask(Definition def, arg_info *args)
{ size_t i, arity = def->functor->arity;

  for(i=0; i<arity; i++)
    def->impl.any.args[i].meta = args[i].meta;

  if ( isTransparentMetamask(def, args) )
    set(def, P_TRANSPARENT);
  else
    clear(def, P_TRANSPARENT);
  set(def, P_META);
}


static int
meta_declaration(term_t spec)
{ GET_LD
  term_t head = PL_new_term_ref();
  term_t arg = PL_new_term_ref();
  Procedure proc;
  atom_t name;
  size_t i, arity;

  if ( !get_procedure(spec, &proc, head, GP_DEFINE) ||
       !PL_get_name_arity(head, &name, &arity) )
    return FALSE;

  arg_info args[arity];			/* GCC dynamic allocation */

  for(i=0; i<arity; i++)
  { atom_t ma;

    _PL_get_arg(i+1, head, arg);

    if ( PL_is_integer(arg) )
    { int e;

      if ( !PL_get_integer_ex(arg, &e) )
	return FALSE;
      if ( e < 0 || e > 9 )
      { domain_error:
	return PL_error(NULL, 0, "0..9",
			ERR_DOMAIN, ATOM_meta_argument_specifier, arg);
      }
      args[i].meta = e;
    } else if ( PL_get_atom(arg, &ma) )
    { int m;

      if      ( ma == ATOM_plus )          m = MA_NONVAR;
      else if ( ma == ATOM_minus )         m = MA_VAR;
      else if ( ma == ATOM_question_mark ) m = MA_ANY;
      else if ( ma == ATOM_star )	   m = MA_ANY; /* * mapped to ? */
      else if ( ma == ATOM_colon )         m = MA_META;
      else if ( ma == ATOM_hat )           m = MA_HAT;
      else if ( ma == ATOM_gdiv )          m = MA_DCG;
      else goto domain_error;

      args[i].meta = m;
    } else
    { return PL_error(NULL, 0, "0..9",
			ERR_TYPE, ATOM_meta_argument_specifier, arg);;
    }
  }

  if ( ReadingSource )
  { SourceFile sf = lookupSourceFile(source_file_name, TRUE);
    return setMetapredicateSource(sf, proc, args PASS_LD);
  } else
  { setMetapredicateMask(proc->definition, args);
    return TRUE;
  }
}


static
PRED_IMPL("meta_predicate", 1, meta_predicate, PL_FA_TRANSPARENT)
{ PRED_LD
  term_t tail = PL_copy_term_ref(A1);
  term_t head = PL_new_term_ref();

  while ( PL_is_functor(tail, FUNCTOR_comma2) )
  { _PL_get_arg(1, tail, head);
    if ( !meta_declaration(head) )
      return FALSE;
    _PL_get_arg(2, tail, tail);
  }

  if ( !meta_declaration(tail) )
    return FALSE;

  return TRUE;
}


static int
unify_meta_argument(term_t head, Definition def, int i ARG_LD)
{ term_t arg = PL_new_term_ref();
  int m = def->impl.any.args[i].meta;

  _PL_get_arg(i+1, head, arg);
  if ( m < 10 )
  { return PL_unify_integer(arg, m);
  } else
  { atom_t a;

    switch(m)
    { case MA_META:	a = ATOM_colon; break;
      case MA_VAR:	a = ATOM_minus; break;
      case MA_ANY:	a = ATOM_question_mark; break;
      case MA_NONVAR:	a = ATOM_plus; break;
      case MA_HAT:	a = ATOM_hat; break;
      case MA_DCG:	a = ATOM_gdiv; break;
      default:		a = NULL_ATOM; assert(0);
    }

    return PL_unify_atom(arg, a);
  }
}


static int
unify_meta_pattern(Procedure proc, term_t head)
{ GET_LD
  Definition def = proc->definition;

  if ( PL_unify_functor(head, def->functor->functor) )
  { int arity = def->functor->arity;
    int i;

    for(i=0; i<arity; i++)
    { if ( !unify_meta_argument(head, def, i PASS_LD) )
	return FALSE;
    }

    return TRUE;
  }

  return FALSE;
}


int
PL_meta_predicate(predicate_t proc, const char *spec_s)
{ Definition def = proc->definition;
  int arity = def->functor->arity;
  int i;
  int mask = 0;
  int transparent = FALSE;
  const unsigned char *s = (const unsigned char*)spec_s;

  for(i=0; i<arity; i++, s++)
  { int spec_c = *s;
    int spec;

    switch(spec_c)
    { case '+':
	spec = MA_NONVAR;
        break;
      case '-':
	spec = MA_VAR;
        break;
      case '?':
	spec = MA_ANY;
        break;
      case ':':
	spec = MA_META;
        break;
      case '^':
	spec = MA_HAT;
        break;
      case '/':
        if ( s[1] == '/' )
	{ spec = MA_DCG;
	  s++;
	  break;
	} else
	{ goto invalid;
	}
      default:
	if ( spec_c >= '0' && spec_c <= '9' )
	{ spec = spec_c - '0';
	  break;
	}
      invalid:
        fatalError("Invalid meta-argument for %s: %s\n", procedureName(proc), spec_s);
	return FALSE;
    }

    def->impl.any.args[i].meta = spec;
    mask |= spec<<(i*4);
    if ( MA_NEEDS_TRANSPARENT(spec) )
      transparent = TRUE;
  }

  if ( transparent )
    set(def, P_TRANSPARENT);
  else
    clear(def, P_TRANSPARENT);
  set(def, P_META);

  return TRUE;
}


void
clear_meta_declaration(Definition def)
{ int i;

  for(i=0; i<def->functor->arity; i++)
    def->impl.any.args[i].meta = MA_ANY;

  clear(def, P_META|P_TRANSPARENT);
}

#ifdef O_CLAUSEGC
		 /*******************************
		 *	     CLAUSE-GC		*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Retracted clauses are  reclaimed  using   the  clause  garbage collector
(CGC). Retract itself merely sets the   erased  generation of the clause
and marks related clause indexes as `dirty'.   CGC  needs to run both to
reclaim the memory and to remove ClauseRef   objects  that point to dead
clauses and thus slow down the  search   for  clauses.  This logic is in
considerClauseGC().

CGC builds on the following components and invariants:

  - Dynamic predicates and static predicates with removed clauses are
    in the table GD->procedures.dirty.
  - CGC does:
    - Set the dirty generation of all dirty predicates to GEN_MAX
    - markPredicatesInEnvironments() finds all referenced predicates
      from frames and pushed explicitly by pushPredicateAccess()
    - Remove all ClauseRefs pointing at clauses removed before the
      oldest active generation from the clause list.  Keep them using
      lingerClauseRef() as someone may be traversing the clause list.
    - Call gcClauseRefs(), which
      - Finds all predicates whose clause-list is being traversed as
        monitored using acquire_def()/release_ref().
      - Call freeClauseRef() for each clause-ref associated with a
        not-being-traversed predicate.  Re-add the others to the
	lingering clause reference list.
      - If freeClauseRef() lowers the clause reference count to zero,
        destroy the clause.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int
considerClauseGC(ARG1_LD)
{ size_t pending  = GD->clauses.erased_size - GD->clauses.erased_size_last;
  size_t codesize = GD->statistics.codes*sizeof(code);
  cgc_stats stats = {0};

  if ( GD->clauses.cgc_space_factor > 0 &&
       pending > codesize/GD->clauses.cgc_space_factor &&
       GD->cleaning == CLN_NORMAL )
  { DEBUG(MSG_CGC_CONSIDER,
	  Sdprintf("CGC? too much garbage: %lld bytes in %lld clauses\n",
		   (int64_t)GD->clauses.erased_size,
		   (int64_t)GD->clauses.erased));
    return TRUE;
  }

  if ( LD->statistics.inferences > LD->clauses.cgc_inferences )
  { int rgc;

    LD->clauses.cgc_inferences = LD->statistics.inferences + 500;

    stats.dirty_pred_clauses = clause_count_in_dirty_predicates(PASS_LD1);
    if ( stats.dirty_pred_clauses == (size_t)-1 )
      return FALSE;			/* already clicked in */

    if ( !cgc_thread_stats(&stats PASS_LD) )
      return FALSE;

    rgc =  ( (double)stats.erased_skipped >
	     (double)stats.local_size*GD->clauses.cgc_stack_factor +
	     (double)stats.dirty_pred_clauses*GD->clauses.cgc_clause_factor );
    rgc = rgc && (GD->cleaning == CLN_NORMAL);
    DEBUG(MSG_CGC_CONSIDER,
	  Sdprintf("GCG? [%s] %ld skipped; lsize=%ld; clauses=%ld\n",
		   rgc ? "Y" : " ",
		   (long)stats.erased_skipped,
		   (long)stats.local_size,
		   (long)stats.dirty_pred_clauses));

    return rgc;
  }

  return FALSE;
}

/** '$cgc_params'(-OldSpace, -OldStack, -OldClause,
 *		  +NewSpace, +NewStack, +NewClause)
 *
 * Query and set the clause GC parameters.
 */

static
PRED_IMPL("$cgc_params", 6, cgc_params, 0)
{ PRED_LD

  return ( PL_unify_integer(A1, GD->clauses.cgc_space_factor) &&
	   PL_unify_float(A2, GD->clauses.cgc_stack_factor) &&
	   PL_unify_float(A3, GD->clauses.cgc_clause_factor) &&
	   PL_get_integer_ex(A4, &GD->clauses.cgc_space_factor) &&
	   PL_get_float_ex(A5, &GD->clauses.cgc_stack_factor) &&
	   PL_get_float_ex(A6, &GD->clauses.cgc_clause_factor) );
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(*) We set the initial oldest_generation to "very old" (0). This ensures
that if a predicate is  registered   dirty  before clause-gc starts, the
oldest generation is 0 and thus no clause reference will be collected.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static void
registerDirtyDefinition(Definition def ARG_LD)
{ if ( false(def, P_DIRTYREG) )
  { DirtyDefInfo ddi = PL_malloc(sizeof(*ddi));

    ddi->oldest_generation = GEN_NEW_DIRTY;		/* see (*) */
    if ( addHTable(GD->procedures.dirty, def, ddi) == ddi )
      set(def, P_DIRTYREG);
    else
      PL_free(ddi);			/* someone else did this */
  }
  if ( !isSignalledGCThread(SIG_CLAUSE_GC PASS_LD) &&	/* already asked for */
       !GD->clauses.cgc_active &&	/* currently running */
       considerClauseGC(PASS_LD1) )
    signalGCThread(SIG_CLAUSE_GC);
}

static void
unregisterDirtyDefinition(Definition def)
{ DirtyDefInfo ddi;

  if ( (ddi=deleteHTable(GD->procedures.dirty, def)) )
  { PL_free(ddi);
    clear(def, P_DIRTYREG);
  }
}


static void
maybeUnregisterDirtyDefinition(Definition def)
{ if ( false(def, P_DYNAMIC) &&
       true(def, P_DIRTYREG) &&
       def->impl.clauses.erased_clauses == 0 )
  { unregisterDirtyDefinition(def);
  }

  if ( true(def, P_ERASED) )
  { DEBUG(MSG_PROC_COUNT, Sdprintf("Delayed unalloc %s\n", predicateName(def)));
    assert(def->module == NULL);
    if ( def->impl.clauses.first_clause == NULL )
    { unregisterDirtyDefinition(def);
      freeHeap(def, sizeof(*def));
    }
  }
}


static int
sum_dirty_clauses(void *n, size_t *countp)
{ Definition def = n;

  if ( GD->clauses.cgc_active )
  { *countp = (size_t)-1;
    return FALSE;
  }

  if ( false(def, P_FOREIGN) &&
       def->impl.clauses.erased_clauses > 0 )
    *countp += def->impl.clauses.number_of_clauses;

  return TRUE;
}


static size_t
clause_count_in_dirty_predicates(ARG1_LD)
{ size_t ccount = 0;

  for_table_as_long_as(GD->procedures.dirty, n, v,
		       sum_dirty_clauses(n, &ccount));

  return ccount;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(*) We set the initial generation to   GEN_MAX  to know which predicates
have been marked. We can only reclaim   clauses  that were erased before
the start generation of the clause garbage collector.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

foreign_t
pl_garbage_collect_clauses(void)
{ GET_LD
  int rc = TRUE;

  if ( GD->procedures.dirty->size > 0 &&
       COMPARE_AND_SWAP(&GD->clauses.cgc_active, FALSE, TRUE) )
  { size_t removed = 0;
    size_t erased_pending = GD->clauses.erased_size;
    double gct, t0 = ThreadCPUTime(LD, CPU_USER);
    gen_t start_gen = global_generation();
    int verbose = truePrologFlag(PLFLAG_TRACE_GC) && !LD->in_print_message;

    if ( verbose )
    { if ( (rc=printMessage(ATOM_informational,
			    PL_FUNCTOR_CHARS, "cgc", 1,
			      PL_CHARS, "start")) == FALSE )
	goto out;
    }

    DEBUG(MSG_CGC, Sdprintf("CGC @ %lld ... ", start_gen));
    DEBUG(MSG_CGC_STACK,
	  { Sdprintf("CGC @ %lld ... ", start_gen);
	    PL_backtrace(5,0);
	  });

					/* sanity-check */
    for_table(GD->procedures.dirty, n, v,
	      { DirtyDefInfo ddi = v;
#ifdef O_DEBUG
		Definition def = n;
#endif

		DEBUG(CHK_SECURE,
		      LOCKDEF(def);
		      checkDefinition(def);
		      UNLOCKDEF(def));
		ddi->oldest_generation = GEN_MAX; /* see (*) */
	      });

    markPredicatesInEnvironments(LD);
#ifdef O_PLMT
    forThreadLocalDataUnsuspended(markPredicatesInEnvironments, 0);
#endif

    DEBUG(MSG_CGC, Sdprintf("(marking done)\n"));

    for_table(GD->procedures.dirty, n, v,
	      { Definition def = n;
		DirtyDefInfo ddi = v;

		if ( false(def, P_FOREIGN) &&
		     def->impl.clauses.erased_clauses > 0 )
		{ size_t del = cleanDefinition(def, ddi, start_gen, &rc);

		  removed += del;
		  DEBUG(MSG_CGC_PRED,
			Sdprintf("cleanDefinition(%s, %s): "
				 "%ld clauses (left %ld)\n",
				 predicateName(def),
				 generationName(ddi->oldest_generation),
				 (long)del,
				 (long)def->impl.clauses.erased_clauses));
		}

		maybeUnregisterDirtyDefinition(def);
	      });

    gcClauseRefs();
    GD->clauses.cgc_count++;
    GD->clauses.cgc_reclaimed	+= removed;
    GD->clauses.cgc_time        += (gct=ThreadCPUTime(LD, CPU_USER) - t0);
    GD->clauses.erased_size_last = GD->clauses.erased_size;

    DEBUG(MSG_CGC, Sdprintf("CGC: removed %ld clauses "
			    "(%ld bytes of %ld pending) in %2f sec.\n",
			    (long)removed,
			    (long)erased_pending - GD->clauses.erased_size,
			    (long)GD->clauses.erased_size,
			    gct));

    if ( verbose )
      rc = printMessage(
	      ATOM_informational,
	      PL_FUNCTOR_CHARS, "cgc", 1,
		PL_FUNCTOR_CHARS, "done", 4,
		  PL_INT64,  (int64_t)removed,
		  PL_INT64,  (int64_t)(erased_pending - GD->clauses.erased_size),
		  PL_INT64,  (int64_t)GD->clauses.erased_size,
		  PL_DOUBLE, gct);

  out:
    GD->clauses.cgc_active = FALSE;
  }

  return rc;
}

#endif /*O_CLAUSEGC*/

#ifdef O_DEBUG
		 /*******************************
		 *	    CHECKING		*
		 *******************************/

word
pl_check_definition(term_t spec)
{ GET_LD
  Procedure proc;
  Definition def;
  int nclauses = 0;
  int nerased = 0;
  int nindexable = 0;
  ClauseRef cref;

  if ( !get_procedure(spec, &proc, 0, GP_FIND) )
    return Sdprintf("$check_definition/1: can't find definition");
  def = getProcDefinition(proc);

  if ( true(def, P_FOREIGN) )
    succeed;

  acquire_def(def);
  for(cref = def->impl.clauses.first_clause; cref; cref = cref->next)
  { Clause clause = cref->value.clause;

    if ( cref->d.key == 0 )
      nindexable++;

    if ( false(clause, CL_ERASED) )
      nclauses++;
    else
      nerased++;
  }
  release_def(def);

  if ( nerased != def->impl.clauses.erased_clauses )
    Sdprintf("%s has %d erased clauses, claims %d\n",
	     predicateName(def), nerased, def->impl.clauses.erased_clauses);

  checkClauseIndexSizes(def, nindexable);

  if ( def->impl.clauses.number_of_clauses != nclauses )
    Sdprintf("%s has inconsistent number_of_clauses (%d, should be %d)",
	     predicateName(def), def->impl.clauses.number_of_clauses, nclauses);

  succeed;
}
#endif /*O_DEBUG*/

		/********************************
		*     UNDEFINED PROCEDURES      *
		*********************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
A dynamic call to `f' in `m' has to be made (via call/1 or from C). This
procedure returns the procedure to be run.   If no such procedure exists
an undefined procedure is created and returned. In this case interpret()
will later call trapUndefined() to generate   an  error message (or link
the procedure from the library via autoload).
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

Procedure
resolveProcedure__LD(functor_t f, Module module ARG_LD)
{ Procedure proc;

  if ( (proc = visibleProcedure(f, module PASS_LD)) )
    return proc;

  return lookupProcedure(f, module);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
autoImport() tries to autoimport  f  into   module  `m'  and returns the
definition if this is possible.

PROBLEM: I'm not entirely  sure  it  is  save  to  deallocated  the  old
definition  structure  in  all  cases.   It  is  not  member of any heap
structure, thus sofar everything  is  alright.   After  a  dynamic  link
interpret()  picks up the new definition pointer, thus this should be ok
as well.  Any other C-code that  does  nasty  things  (non-deterministic
code  perhaps,  calls  indirect via C? (I do recall once conciously have
decided its not save, but can't recall why ...)

Its definitely not safe in MT context as   others  may be racing for the
definition.  How  do  we  get   this    working   without   locking  the
proc->definition fetch?
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

Definition
autoImport(functor_t f, Module m)
{ GET_LD
  Procedure proc;
  Definition def, odef;
  ListCell c;
					/* Defined: no problem */
  if ( (proc = isCurrentProcedure(f, m)) && isDefinedProcedure(proc) )
    return proc->definition;

  for(c=m->supers; c; c=c->next)
  { Module s = c->value;

    if ( (def = autoImport(f, s)) )
      goto found;
  }
  return NULL;

found:
  if ( proc == NULL )			/* Create header if not there */
  { if ( !(proc = lookupProcedure(f, m)) )
      return NULL;
  }
					/* Now, take the lock also used */
					/* by lookupProcedure().  Note */
					/* that another thread may have */
					/* done the job for us. */
  LOCKMODULE(m);
  if ( (odef=proc->definition) != def )	/* Nope, we must link the def */
  { proc->definition = def;
    shareDefinition(def);

    if ( unshareDefinition(odef) == 0 )
    {
#ifdef O_PLMT
      PL_LOCK(L_THREAD);
      if ( (GD->statistics.threads_created -
	    GD->statistics.threads_finished) == 1 )
      { DEBUG(MSG_PROC_COUNT, Sdprintf("Unalloc %s\n", predicateName(odef)));
	unregisterDirtyDefinition(odef);
	freeHeap(odef, sizeof(*odef));
	GD->statistics.predicates--;
      } else
      { DEBUG(MSG_PROC, Sdprintf("autoImport(%s,%s): Linger %s (%p)\n",
				 functorName(f), PL_atom_chars(m->name),
				 predicateName(odef), odef));
	lingerDefinition(odef);
      }
      PL_UNLOCK(L_THREAD);
#else
      freeHeap(odef, sizeof(struct definition));
#endif
    }
  }
  UNLOCKMODULE(m);

  return def;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Call the autoloader for the given definition.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static atom_t
autoLoader(Definition def)
{ GET_LD
  fid_t  cid;
  term_t argv;
  qid_t qid;
  atom_t answer = ATOM_nil;

  if ( !GD->procedures.undefinterc4 )
    GD->procedures.undefinterc4 = PL_pred(FUNCTOR_undefinterc4,
					  MODULE_system);

  if ( !(cid  = PL_open_foreign_frame()) ||
       !(argv = PL_new_term_refs(4)) )
    return answer;

  PL_put_atom(    argv+0, def->module->name);
  PL_put_atom(    argv+1, def->functor->name);
  PL_put_integer( argv+2, def->functor->arity);

  push_input_context(ATOM_autoload);
  LD->autoload_nesting++;
  if ( (qid = PL_open_query(MODULE_system, PL_Q_NODEBUG,
			    GD->procedures.undefinterc4, argv)) )
  { if ( PL_next_solution(qid) )
      PL_get_atom(argv+3, &answer);
    PL_close_query(qid);
  }
  LD->autoload_nesting--;
  pop_input_context();
  PL_discard_foreign_frame(cid);

  return answer;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
According to Paulo Moura, predicates defined either dynamic, multifile or
discontiguous should not cause an undefined predicate warning.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

Definition
trapUndefined(Definition def ARG_LD)
{ int retry_times = 0;
  Definition newdef;
  Module module = def->module;
  FunctorDef functor = def->functor;

  retry:
					/* Auto import */
  if ( (newdef = autoImport(functor->functor, module)) )
    return newdef;
					/* Pred/Module does not want to trap */
  if ( true(def, PROC_DEFINED) ||
       getUnknownModule(module) == UNKNOWN_FAIL )
    return def;

  DEBUG(5, Sdprintf("trapUndefined(%s)\n", predicateName(def)));

					/* Trap via exception/3 */
  if ( truePrologFlag(PLFLAG_AUTOLOAD) && !GD->bootsession )
  { if ( LD->autoload_nesting > 100 )
    { LD->autoload_nesting = 1;
      sysError("trapUndefined(): undefined: %s", predicateName(def));

      return def;
    } else
    { atom_t answer = autoLoader(def);

      def = lookupDefinition(functor->functor, module);

      if ( answer == ATOM_fail )
      { return def;
      } else if ( answer == ATOM_error )
      { goto error;
      } else if ( answer == ATOM_retry )
      { if ( retry_times++ )
	{ warning("[Thread %d]: exception handler failed to define %s\n",
		  PL_thread_self(),
		  predicateName(def));
	  return def;
	}
	goto retry;
      }
    }
  }
				/* No one wants to intercept */
error:
  if ( GD->bootsession )
  { sysError("Undefined predicate: %s", predicateName(def));
  } else
  { createUndefSupervisor(def);
  }

  return def;
}


		 /*******************************
		 *	  REQUIRE SUPPORT	*
		 *******************************/

word
pl_require(term_t pred)
{ Procedure proc;

  if ( !get_procedure(pred, &proc, 0, GP_RESOLVE) )
    return get_procedure(pred, &proc, 0, GP_DEFINE);

  succeed;
}


		/********************************
		*            RETRACT            *
		*********************************/

typedef struct
{ Definition def;
  struct clause_choice chp;
  int allocated;
} retract_context;

static retract_context *
alloc_retract_context(retract_context *ctx0)
{ retract_context *ctx = allocForeignState(sizeof(*ctx));

  *ctx = *ctx0;
  ctx->allocated = TRUE;

  return ctx;
}

static void
free_retract_context(retract_context *ctx ARG_LD)
{ popPredicateAccess(ctx->def);
  leaveDefinition(ctx->def);

  if ( ctx->allocated )
    freeForeignState(ctx, sizeof(*ctx));
}

static
PRED_IMPL("retract", 1, retract,
	  PL_FA_TRANSPARENT|PL_FA_NONDETERMINISTIC|PL_FA_ISO)
{ PRED_LD
  term_t term = A1;
  retract_context ctxbuf;
  retract_context *ctx;
  ClauseRef cref;

  if ( CTX_CNTRL == FRG_CUTTED )
  { ctx = CTX_PTR;

    free_retract_context(ctx PASS_LD);

    return TRUE;
  } else
  { Module m = NULL;
    term_t cl = PL_new_term_ref();
    term_t head = PL_new_term_ref();
    term_t body = PL_new_term_ref();
    Word argv;
    atom_t b;
    fid_t fid;

    if ( !PL_strip_module_ex(term, &m, cl) ||
	 !get_head_and_body_clause(cl, head, body, NULL PASS_LD) )
      return FALSE;
    if ( PL_get_atom(body, &b) && b == ATOM_true )
      PL_put_term(cl, head);

    argv = valTermRef(head);
    deRef(argv);
    if ( isTerm(*argv) )		/* retract(foobar(a1, ...)) */
      argv = argTermP(*argv, 0);
    else
      argv = NULL;			/* retract(foobar) */

    if ( CTX_CNTRL == FRG_FIRST_CALL )
    { functor_t fd;
      Procedure proc;
      Definition def;

      if ( !PL_get_functor(head, &fd) )
	return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_callable, head);
      if ( !(proc = isCurrentProcedure(fd, m)) )
      { checkModifySystemProc(fd);
	fail;
      }

      def = getProcDefinition(proc);

      if ( true(def, P_FOREIGN) )
	return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);
      if ( false(def, P_DYNAMIC) )
      { if ( isDefinedProcedure(proc) )
	  return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);
	setDynamicDefinition(def, TRUE); /* implicit */
	fail;				/* no clauses */
      }

      enterDefinition(def);			/* reference the predicate */
      setGenerationFrameVal(environment_frame, pushPredicateAccess(def));
      cref = firstClause(argv, environment_frame, def, &ctxbuf.chp PASS_LD);
      if ( !cref )
      { popPredicateAccess(def);
	leaveDefinition(def);
	fail;
      }

      ctx = &ctxbuf;
      ctx->def = def;
      ctx->allocated = 0;
    } else
    { ctx  = CTX_PTR;
      cref = nextClause(&ctx->chp, argv, environment_frame, ctx->def);
    }

    if ( !(fid = PL_open_foreign_frame()) )
    { free_retract_context(ctx PASS_LD);
      return FALSE;
    }

    while( cref )
    { if ( decompile(cref->value.clause, cl, 0) )
      { if ( retractClauseDefinition(ctx->def, cref->value.clause) ||
	     CTX_CNTRL != FRG_FIRST_CALL )
	{ if ( !ctx->chp.cref )		/* deterministic last one */
	  { free_retract_context(ctx PASS_LD);
	    PL_close_foreign_frame(fid);
	    return TRUE;
	  }

	  if ( ctx == &ctxbuf )		/* non-determinisic; save state */
	    ctx = alloc_retract_context(ctx);

	  PL_close_foreign_frame(fid);
	  ForeignRedoPtr(ctx);
	} else
	{ setGenerationFrame(environment_frame);
	}
      }

      if ( PL_exception(0) )
	break;

      PL_rewind_foreign_frame(fid);
      cref = nextClause(&ctx->chp, argv, environment_frame, ctx->def);
    }

    PL_close_foreign_frame(fid);
    free_retract_context(ctx PASS_LD);
    return FALSE;
  }
}


static int
allVars(int argc, Word argv ARG_LD)
{ int i, r, allvars = TRUE;
  Word *reset = alloca(argc*sizeof(Word));

  for(i=0; i<argc; i++)
  { Word p2;

    deRef2(argv+i, p2);
    if ( isVar(*p2) )
    { reset[i] = p2;
      *p2 = ATOM_nil;
    } else
    { allvars = FALSE;
      break;
    }
  }

  for(r=0; r<i; r++)
    setVar(*reset[r]);

  return allvars;
}


word
pl_retractall(term_t head)
{ GET_LD
  term_t thehead = PL_new_term_ref();
  Procedure proc;
  Definition def;
  ClauseRef cref;
  Word argv;
  int allvars = TRUE;
  fid_t fid;

  if ( !get_procedure(head, &proc, thehead, GP_CREATE) )
    fail;

  def = getProcDefinition(proc);
  if ( true(def, P_FOREIGN) )
    return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);
  if ( false(def, P_DYNAMIC) )
  { if ( isDefinedProcedure(proc) )
      return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);
    if ( !setDynamicDefinition(def, TRUE) )
      fail;
    succeed;				/* nothing to retract */
  }

  argv = valTermRef(thehead);
  deRef(argv);
  if ( isTerm(*argv) )
  { int arity = arityTerm(*argv);
    argv = argTermP(*argv, 0);

    allvars = allVars(arity, argv PASS_LD);
  } else
  { allvars = TRUE;
    argv = NULL;
  }

  startCritical;
  enterDefinition(def);
  setGenerationFrameVal(environment_frame, pushPredicateAccess(def));
  fid = PL_open_foreign_frame();

  DEBUG(CHK_SECURE,
	LOCKDEF(def);
	checkDefinition(def);
        UNLOCKDEF(def));
  if ( allvars )
  { gen_t gen = generationFrame(environment_frame);

    acquire_def(def);
    for(cref = def->impl.clauses.first_clause; cref; cref = cref->next)
    { if ( visibleClauseCNT(cref->value.clause, gen) )
      { retractClauseDefinition(def, cref->value.clause);
      }
    }
    release_def(def);
  } else
  { struct clause_choice chp;

    if ( !(cref = firstClause(argv, environment_frame, def, &chp PASS_LD)) )
    { int rc = endCritical;
      popPredicateAccess(def);
      leaveDefinition(def);
      return rc;
    }

    while( cref )
    { if ( decompileHead(cref->value.clause, thehead) )
	retractClauseDefinition(def, cref->value.clause);

      PL_rewind_foreign_frame(fid);

      if ( !chp.cref )
      { popPredicateAccess(def);
	leaveDefinition(def);
	return endCritical;
      }

      if ( argv )				/* may be shifted */
      { argv = valTermRef(thehead);
	argv = argTermP(*argv, 0);
      }

      cref = nextClause(&chp, argv, environment_frame, def);
    }
  }
  popPredicateAccess(def);
  leaveDefinition(def);
  DEBUG(CHK_SECURE,
	LOCKDEF(def);
	checkDefinition(def);
	UNLOCKDEF(def));

  return endCritical;
}

		/********************************
		*       PROLOG PREDICATES       *
		*********************************/

static word
do_abolish(Module m, term_t atom, term_t arity)
{ GET_LD
  functor_t f;
  Procedure proc;
  atom_t name;
  int a = 0;

  if ( !PL_get_atom_ex(atom, &name) ||
       !get_arity(arity, 0, MAXARITY, &a) )
    fail;

  if ( !(f = isCurrentFunctor(name, a)) )
    succeed;
  if ( !checkModifySystemProc(f) )
    fail;
  if ( !(proc = isCurrentProcedure(f, m)) )
    succeed;

  if ( truePrologFlag(PLFLAG_ISO) && false(proc->definition, P_DYNAMIC) )
    return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, proc);

  return abolishProcedure(proc, m);
}


word
pl_abolish(term_t name, term_t arity)	/* Name, Arity */
{ GET_LD
  Module m = NULL;

  return ( PL_strip_module(name, &m, name) &&
	   do_abolish(m, name, arity)
	 );
}


word
pl_abolish1(term_t spec)		/* Name/Arity */
{ GET_LD
  term_t name  = PL_new_term_ref();
  term_t arity = PL_new_term_ref();
  Module m = NULL;

  if ( !PL_strip_module(spec, &m, spec) )
    return FALSE;

  if ( !PL_is_functor(spec, FUNCTOR_divide2) )
    return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_predicate_indicator, spec);

  _PL_get_arg(1, spec, name);
  _PL_get_arg(2, spec, arity);

  return do_abolish(m, name, arity);
}


typedef struct patt_mask
{ atom_t	key;
  unsigned int  mask;
} patt_mask;

#define TRACE_ANY (TRACE_CALL|TRACE_REDO|TRACE_EXIT|TRACE_FAIL)

static const patt_mask patt_masks[] =
{ { ATOM_dynamic,	   P_DYNAMIC },
  { ATOM_multifile,	   P_MULTIFILE },
  { ATOM_locked,	   P_LOCKED },
  { ATOM_system,	   P_LOCKED },		/* compatibility */
  { ATOM_spy,		   SPY_ME },
  { ATOM_trace,		   TRACE_ME },
  { ATOM_trace_call,	   TRACE_CALL },
  { ATOM_trace_redo,	   TRACE_REDO },
  { ATOM_trace_exit,	   TRACE_EXIT },
  { ATOM_trace_fail,	   TRACE_FAIL },
  { ATOM_trace_any,	   TRACE_ANY },
  { ATOM_hide_childs,	   HIDE_CHILDS },
  { ATOM_transparent,	   P_TRANSPARENT },
  { ATOM_discontiguous,	   P_DISCONTIGUOUS },
  { ATOM_volatile,	   P_VOLATILE },
  { ATOM_thread_local,	   P_THREAD_LOCAL },
  { ATOM_noprofile,	   P_NOPROFILE },
  { ATOM_iso,		   P_ISO },
  { ATOM_public,	   P_PUBLIC },
  { ATOM_non_terminal,	   P_NON_TERMINAL },
  { ATOM_quasi_quotation_syntax, P_QUASI_QUOTATION_SYNTAX },
  { ATOM_clausable,	   P_CLAUSABLE },
  { (atom_t)0,		   0 }
};

static unsigned int
attribute_mask(atom_t key)
{ const patt_mask *p;

  for(p=patt_masks; p->key; p++)
  { if ( p->key == key )
      return p->mask;
  }

  { GET_LD
    term_t t;

    return ( (t = PL_new_term_ref()) &&
	     PL_put_atom(t, key) &&
	     PL_domain_error("predicate_property", t)
	   );
  }
}


static size_t
num_visible_clauses(Definition def, atom_t key)
{ GET_LD;

  if ( LD->gen_reload != GEN_INVALID )
  { ClauseRef c;
    size_t num_clauses = 0;

    acquire_def(def);
    for(c = def->impl.clauses.first_clause; c; c = c->next)
    { Clause cl = c->value.clause;
      if ( key == ATOM_number_of_rules && true(cl, UNIT_CLAUSE) )
        continue;
      if ( visibleClause(cl, generationFrame(environment_frame)) )
        num_clauses++;
    }
    release_def(def);
    return num_clauses;
  }

  if ( key == ATOM_number_of_clauses )
    return def->impl.clauses.number_of_clauses;
  else
    return def->impl.clauses.number_of_rules;
}


word
pl_get_predicate_attribute(term_t pred,
			   term_t what, term_t value)
{ GET_LD
  Procedure proc;
  Definition def;
  functor_t fd;
  atom_t key;
  Module module = (Module) NULL;
  unsigned int att;
  term_t head = PL_new_term_ref();

  if ( !PL_strip_module(pred, &module, head) ||
       !PL_get_functor(head, &fd) ||
       !(proc = resolveProcedure(fd, module)) )
    fail;

  def = proc->definition;

  if ( !PL_get_atom(what, &key) )
    return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_atom, what);

  if ( key == ATOM_imported )
  { if ( module == def->module )
      fail;
    return PL_unify_atom(value, def->module->name);
  } else if ( key == ATOM_indexed )
  { return unify_index_pattern(proc, value);
  } else if ( key == ATOM_meta_predicate )
  { if ( false(def, P_META) )
      fail;
    return unify_meta_pattern(proc, value);
  } else if ( key == ATOM_exported )
  { return PL_unify_integer(value, isPublicModule(module, proc));
  } else if ( key == ATOM_defined )
  { int d;

    if ( isDefinedProcedureSource(proc) )
      d = 1;
    else
      d = 0;

    return PL_unify_integer(value, d);
  } else if ( key == ATOM_line_count || key == ATOM_file )
  { int line;
    Clause clause;
    int rc = FALSE;

    if ( false(def, P_FOREIGN|P_THREAD_LOCAL) )
    { acquire_def(def);
      if ( def->impl.clauses.first_clause &&
	   (clause = def->impl.clauses.first_clause->value.clause) &&
	   (line=clause->line_no) )
      { if ( key == ATOM_line_count )
	{ rc = PL_unify_integer(value, line);
	} else
	{ SourceFile sf = indexToSourceFile(clause->source_no);

	  if ( sf )
	    rc = PL_unify_atom(value, sf->name);
	}
      }
      release_def(def);
    }

    return rc;
  } else if ( key == ATOM_foreign )
  { return PL_unify_integer(value, true(def, P_FOREIGN) ? 1 : 0);
  } else if ( key == ATOM_number_of_clauses )
  { size_t num_clauses;
    if ( def->flags & P_FOREIGN )
      fail;

    def = getProcDefinition(proc);
    num_clauses = num_visible_clauses(def, key);
    if ( num_clauses == 0 && false(def, P_DYNAMIC) )
      fail;
    return PL_unify_int64(value, num_clauses);
  } else if ( key == ATOM_last_modified_generation )
  { if ( def->flags & P_FOREIGN )
      fail;
    def = getProcDefinition(proc);
    return PL_unify_int64(value, def->last_modified);
  } else if ( key == ATOM_number_of_rules )
  { if ( def->flags & P_FOREIGN )
      fail;

    def = getProcDefinition(proc);
    if ( def->impl.clauses.number_of_clauses == 0 && false(def, P_DYNAMIC) )
      fail;
    return PL_unify_integer(value, num_visible_clauses(def, key));
  } else if ( (att = attribute_mask(key)) )
  { return PL_unify_integer(value, (def->flags & att) ? 1 : 0);
  } else
  { return FALSE;
  }
}


static int
setDynamicDefinition_unlocked(Definition def, bool isdyn)
{ GET_LD

  if ( ( isdyn &&  true(def, P_DYNAMIC)) ||
       (!isdyn && false(def, P_DYNAMIC)) )
    return TRUE;

  if ( isdyn )				/* static --> dynamic */
  { if ( truePrologFlag(PLFLAG_PROTECT_STATIC_CODE) &&
	 hasClausesDefinition(def) )
      return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PREDICATE, def);

    set(def, P_DYNAMIC);
    freeCodesDefinition(def, TRUE);	/* reset to S_VIRGIN */
    registerDirtyDefinition(def PASS_LD);	/* always considered dirty */
  } else				/* dynamic --> static */
  { clear(def, P_DYNAMIC);
    freeCodesDefinition(def, TRUE);	/* reset to S_VIRGIN */
  }

  return TRUE;
}


int
setDynamicDefinition(Definition def, bool isdyn)
{ int rc;

  LOCKDEF(def);
  rc = setDynamicDefinition_unlocked(def, isdyn);
  UNLOCKDEF(def);

  return rc;
}

int
setThreadLocalDefinition(Definition def, bool val)
{
#ifdef O_PLMT

  LOCKDEF(def);
  if ( (val && true(def, P_THREAD_LOCAL)) ||
       (!val && false(def, P_THREAD_LOCAL)) )
  { UNLOCKDEF(def);
    return TRUE;
  }

  if ( val )				/* static --> local */
  { if ( def->impl.clauses.first_clause )
    { UNLOCKDEF(def);
      return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PREDICATE, def);
    }
    set(def, P_DYNAMIC|P_VOLATILE|P_THREAD_LOCAL);

    def->codes = SUPERVISOR(thread_local);
    def->impl.local = new_ldef_vector();

    UNLOCKDEF(def);
    return TRUE;
  } else				/* local --> static */
  { UNLOCKDEF(def);
    return PL_error(NULL, 0, "predicate is thread-local",
		    ERR_MODIFY_STATIC_PREDICATE, def);
  }
#else
  setDynamicDefinition(def, val);

  if ( val )
    set(def, P_VOLATILE|P_THREAD_LOCAL);
  else
    clear(def, P_VOLATILE|P_THREAD_LOCAL);

  succeed;
#endif
}


static int
setClausableDefinition(Definition def, int val)
{ GET_LD

  if ( val )
  { if ( truePrologFlag(PLFLAG_PROTECT_STATIC_CODE) &&
	 hasClausesDefinition(def) )
      return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PREDICATE, def);
    set(def, P_CLAUSABLE);
  } else
  { clear(def, P_CLAUSABLE);
  }

  return TRUE;
}

int
setAttrDefinition(Definition def, unsigned attr, int val)
{ int rc;

  if ( attr == P_DYNAMIC )
  { rc = setDynamicDefinition(def, val);
  } else if ( attr == P_THREAD_LOCAL )
  { rc = setThreadLocalDefinition(def, val);
  } else if ( attr == P_CLAUSABLE )
  { rc = setClausableDefinition(def, val);
  } else
  { if ( !val )
    { clear(def, attr);
    } else
    { set(def, attr);
    }

    rc = TRUE;
  }

  return rc;
}


static int
get_bool_or_int_ex(term_t t, int *val ARG_LD)
{ if ( PL_get_bool(t, val) )
    return TRUE;
  if ( PL_get_integer(t, val) && !(*val & ~1) )
    return TRUE;			/* accept 0 and 1 */
  return PL_get_bool_ex(t, val);	/* generate an error */
}


word
pl_set_predicate_attribute(term_t pred, term_t what, term_t value)
{ GET_LD
  Procedure proc;
  Definition def;
  atom_t key;
  int val;
  uintptr_t att;

  if ( !PL_get_atom_ex(what, &key) ||
       !get_bool_or_int_ex(value, &val PASS_LD) ||
       !(att = attribute_mask(key)) )
    return FALSE;

  if ( att & (TRACE_ANY|SPY_ME) )
  { if ( !get_procedure(pred, &proc, 0, GP_RESOLVE) )
      fail;
  } else
  { if ( !get_procedure(pred, &proc, 0, GP_DEFINE|GP_NAMEARITY) )
      fail;
  }
  def = proc->definition;

  if ( ReadingSource )
  { SourceFile sf = lookupSourceFile(source_file_name, TRUE);
    return setAttrProcedureSource(sf, proc, att, val PASS_LD);
  } else
  { return setAttrDefinition(def, att, val);
  }
}


word
pl_default_predicate(term_t d1, term_t d2)
{ Procedure p1, p2;

  if ( get_procedure(d1, &p1, 0, GP_FIND) &&
       get_procedure(d2, &p2, 0, GP_FIND) )
  { if ( p1->definition == p2->definition || !isDefinedProcedure(p1) )
      succeed;
  }

  fail;
}


static
PRED_IMPL("$get_clause_attribute", 3, get_clause_attribute, 0)
{ GET_LD
  Clause clause;
  atom_t a;

  term_t ref   = A1;
  term_t att   = A2;
  term_t value = A3;

  if ( !PL_get_clref(ref, &clause) ||
       !PL_get_atom_ex(att, &a) )
    return FALSE;

  if ( a == ATOM_line_count )
  { if ( clause->line_no )
      return PL_unify_integer(value, clause->line_no);
  } else if ( a == ATOM_file )
  { SourceFile sf = indexToSourceFile(clause->source_no);

    if ( sf )
      return PL_unify_atom(value, sf->name);
  } else if ( a == ATOM_owner )
  { SourceFile sf = indexToSourceFile(clause->owner_no);

    if ( sf )
      return PL_unify_atom(value, sf->name);
  } else if ( a == ATOM_size )
  { size_t size = sizeofClause(clause->code_size);

    return PL_unify_int64(value, size);
  } else if ( a == ATOM_fact )
  { return PL_unify_atom(value,
			 true(clause, UNIT_CLAUSE) ? ATOM_true
						   : ATOM_false);
  } else if ( a == ATOM_erased )
  { atom_t erased;

    if ( visibleClause(clause, generationFrame(environment_frame)) )
      erased = ATOM_false;
    else
      erased = ATOM_true;

    return PL_unify_atom(value, erased);
  } else if ( a == ATOM_predicate_indicator )
  { if ( unify_definition(MODULE_user, value,
			  clause->predicate, 0,
			  GP_QUALIFY|GP_NAMEARITY) )
      return TRUE;
  } else if ( a == ATOM_module )
  { return PL_unify_atom(value, clauseBodyContext(clause)->name);
  }

  fail;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
redefineProcedure() is called when a procedure   needs to be defined and
it seems to have a definition.

Sf is the `owning' source-file

(*) occurs if this is actually false. This   happens if a file holding a
running predicate is reloaded because the clauses cannot be wiped.
(**) there is a definition, but we are reloading and we have not yet
seen this predicate, so it isn't there.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

int
redefineProcedure(Procedure proc, SourceFile sf, unsigned int suppress)
{ GET_LD
  Definition def = proc->definition;

  if ( true(def, P_FOREIGN) )
  {			/* first call printMessage() */
			/* so we can provide info about the old definition */
    if ( !printMessage(ATOM_warning,
		       PL_FUNCTOR_CHARS, "redefined_procedure", 2,
		         PL_CHARS, "foreign",
		         _PL_PREDICATE_INDICATOR, proc) )
      return FALSE;
			/* ... then abolish */
    abolishProcedure(proc, def->module);
  } else if ( false(def, P_MULTIFILE) )
  { ClauseRef first;

    def = getProcDefinition__LD(def PASS_LD);
    if ( !(first = hasClausesDefinition(def)) )
      return TRUE;				/* (*) see above */

    if ( first->value.clause->owner_no == sf->index )
    { if ( sf->reload && !reloadHasClauses(sf, proc PASS_LD) )
	return TRUE;				/* (**) see above */

      if ( ((debugstatus.styleCheck & ~suppress) & DISCONTIGUOUS_STYLE) &&
	   false(def, P_DISCONTIGUOUS) &&
	   sf->current_procedure )
      { if ( !printMessage(ATOM_warning,
			   PL_FUNCTOR_CHARS, "discontiguous", 2,
			     _PL_PREDICATE_INDICATOR, proc,
			     _PL_PREDICATE_INDICATOR, sf->current_procedure) )
	  return FALSE;
      }
    } else if ( !hasProcedureSourceFile(sf, proc) )
    { if ( true(def, P_THREAD_LOCAL) )
	return PL_error(NULL, 0, NULL, ERR_MODIFY_THREAD_LOCAL_PROC, proc);

      if ( first )
      { if ( !printMessage(ATOM_warning,
			   PL_FUNCTOR_CHARS, "redefined_procedure", 2,
			     PL_CHARS, "static",
			     _PL_PREDICATE_INDICATOR, proc) )
	  return FALSE;
      }
			/* again, _after_ the printMessage() */
      abolishProcedure(proc, def->module);
    }
  }

  return TRUE;
}



/** copy_predicate(From:predicate_indicator, To:predicate_indicator) is det.

Copy all clauses of From into To. To is created as a dynamic predicate.
*/

static void
remoduleClause(Clause cl, Module old, Module new)
{ Code PC, end;
  int in_body = FALSE;

  if ( true(cl, UNIT_CLAUSE) )
    return;

  PC  = cl->codes;
  end = &PC[cl->code_size];
  for( ; PC < end; PC = stepPC(PC) )
  { code op = fetchop(PC);

    if ( in_body )
    { const char *ats=codeTable[op].argtype;
      int an;

      for(an=0; ats[an]; an++)
      { switch(ats[an])
	{ case CA1_PROC:
	  { Procedure op = (Procedure)PC[an+1];

	    if ( op->definition->module != MODULE_system )
	    { functor_t f = op->definition->functor->functor;

	      PC[an+1] = (code)lookupProcedure(f, new);
	    }
	    break;
	  }
	  case CA1_MODULE:
	  { if ( old == (Module)PC[an+1] )
	      PC[an+1] = (code)new;
	  }
	}
      }
    } else if ( op == I_ENTER )
    { in_body = TRUE;
    }
  }
}


static
PRED_IMPL("copy_predicate_clauses", 2, copy_predicate_clauses, PL_FA_TRANSPARENT)
{ PRED_LD
  Procedure from, to;
  Definition def, copy_def;
  ClauseRef cref;
  gen_t generation;

  if ( !get_procedure(A1, &from, 0, GP_NAMEARITY|GP_RESOLVE) )
    fail;
  if ( !isDefinedProcedure(from) )
    trapUndefined(getProcDefinition(from) PASS_LD);
  def = getProcDefinition(from);
  generation = global_generation();		/* take a consistent snapshot */

  if ( true(def, P_FOREIGN) )
    return PL_error(NULL, 0, NULL, ERR_PERMISSION_PROC,
		    ATOM_access, ATOM_private_procedure, from);

  if ( !get_procedure(A2, &to, 0, GP_NAMEARITY|GP_CREATE) )
    return FALSE;

  copy_def = getProcDefinition(to);
  if ( true(copy_def, P_FOREIGN) )
    return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, to);
  if ( false(copy_def, P_DYNAMIC) )
  { if ( isDefinedProcedure(to) )
      return PL_error(NULL, 0, NULL, ERR_MODIFY_STATIC_PROC, to);
    if ( !setDynamicDefinition(copy_def, TRUE) )
      fail;
  }

  enterDefinition(def);
  acquire_def(def);
  for( cref = def->impl.clauses.first_clause; cref; cref = cref->next )
  { Clause cl = cref->value.clause;

    if ( visibleClause(cl, generation) )
    { size_t size = sizeofClause(cl->code_size);
      Clause copy = PL_malloc_atomic(size);

      memcpy(copy, cl, size);
      copy->predicate = copy_def;
      if ( def->module != copy_def->module )
	remoduleClause(copy, def->module, copy_def->module);
#ifdef O_ATOMGC
#ifdef O_DEBUG_ATOMGC
      forAtomsInClause(copy, register_atom_clause);
#else
      forAtomsInClause(copy, PL_register_atom);
#endif
#endif
      assertProcedure(to, copy, CL_END PASS_LD);
    }
  }
  release_def(def);
  leaveDefinition(def);

  return TRUE;
}


#if defined(O_MAINTENANCE) || defined(O_DEBUG)

		 /*******************************
		 *	INTERNAL DEBUGGING	*
		 *******************************/


static void
listGenerations(Definition def)
{ GET_LD
  gen_t gen = generationFrame(environment_frame);
  ClauseRef cref;
  int i;

  Sdprintf("%s has %d clauses at generation %ld\n",
	   predicateName(def),
	   def->impl.clauses.number_of_clauses, gen);

  acquire_def(def);
  for(i=1,cref=def->impl.clauses.first_clause; cref; cref=cref->next, i++)
  { Clause clause = cref->value.clause;

    Sdprintf("%p: [%2d] %8u-%10u%s%s%s\n",
	     clause, i,
	     clause->generation.created,
	     clause->generation.erased,
	     true(clause, CL_ERASED) ? " erased" : "",
	     visibleClause(clause, gen) ? " v " : " X ",
	     keyName(cref->d.key));
  }
  release_def(def);

  listIndexGenerations(def, gen);
}


void
checkDefinition(Definition def)
{ GET_LD
  unsigned int nc, indexed = 0;
  ClauseRef cref;
  unsigned int erased = 0;
  Definition old;

						/* check basic clause list */
  acquire_def2(def, old);
  for(nc=0, cref = def->impl.clauses.first_clause; cref; cref=cref->next)
  { Clause clause = cref->value.clause;

    if ( false(clause, CL_ERASED) )
    { if ( cref->d.key )
	indexed++;
      nc++;
    } else
    { erased++;
    }
  }
  release_def2(def, old);

  assert(nc == def->impl.clauses.number_of_clauses);
  assert(erased == def->impl.clauses.erased_clauses);

  checkClauseIndexes(def);
}


foreign_t
pl_check_procedure(term_t desc)
{ GET_LD
  Procedure proc;
  Definition def;

  if ( !get_procedure(desc, &proc, 0, GP_FIND|GP_NAMEARITY) )
    fail;
  def = getProcDefinition(proc);

  if ( true(def, P_FOREIGN) )
    fail;

  LOCKDEF(def);
  checkDefinition(def);
  UNLOCKDEF(def);

  succeed;
}


foreign_t
pl_list_generations(term_t desc)
{ GET_LD
  Procedure proc;
  Definition def;

  if ( !get_procedure(desc, &proc, 0, GP_FIND|GP_NAMEARITY) )
    fail;
  def = getProcDefinition(proc);

  if ( true(def, P_FOREIGN) )
    fail;				/* permission error */

  listGenerations(def);

  succeed;
}


#endif /*O_MAINTENANCE*/


		 /*******************************
		 *      PUBLISH PREDICATES	*
		 *******************************/

BeginPredDefs(proc)
  PRED_DEF("meta_predicate", 1, meta_predicate, PL_FA_TRANSPARENT)
  PRED_DEF("$get_clause_attribute", 3, get_clause_attribute, 0)
  PRED_DEF("retract", 1, retract,
	   PL_FA_TRANSPARENT|PL_FA_NONDETERMINISTIC|PL_FA_ISO)
  PRED_DEF("copy_predicate_clauses", 2, copy_predicate_clauses, PL_FA_TRANSPARENT)
  PRED_DEF("$cgc_params", 6, cgc_params, 0)
EndPredDefs