yap-6.3/os/pl-prologflag.c

/*  $Id$

    Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.wielemaker@uva.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 1985-2008, 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

/*#define O_DEBUG 1*/
#include "pl-incl.h"
#ifdef __YAP_PROLOG__
#include "pl-ctype.h"
#else
#include "os/pl-ctype.h"
#endif
#include <ctype.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#ifdef __WINDOWS__
#include <process.h>			/* getpid() */
#endif

#define LOCK()   PL_LOCK(L_PLFLAG)
#define UNLOCK() PL_UNLOCK(L_PLFLAG)


		 /*******************************
		 *	PROLOG FLAG HANDLING	*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
ISO Prolog flags are properties of the   running  Prolog system. Some of
these flags can be set  by  the   user,  such  as whether read/1 honours
character-escapes, whether garbage-collection is enabled,  etc. Some are
global and read-only, such as whether the operating system is unix.

In  the  multi-threading  version,  Prolog  flags  have  to  be  changed
thread-local. Therefore two flag-tables have been  defined: a global one
which is used as long as there is only  one thread, and a local one that
is used to write changes to  after   multiple  threads  exist. On thread
creation this table is copied from  the   parent  and on destruction the
local table is destroyed.  Note  that   the  flag-mask  for  fast access
(truePrologFlag(*PLFLAG_)) is always copied to the local thread-data.

Altogether  this  module  is  a  bit  too  complex,  but  I  see  little
alternative. I considered creating  copy-on-write   hash-tables,  but in
combination to the table-enumator  objects  this   proves  very  hard to
implement safely. Using plain Prolog is not  a good option too: they are
used before we can  use  any  Prolog   at  startup,  predicates  are not
thread-local and some of the prolog flags  require very fast access from
C (the booleans in the mask).

Just using a local table and  copy   it  on  thread-creation would be an
option, but 90% of the prolog flags   are read-only or never changed and
we want to be able to have a lot of flags and don't harm thread_create/3
too much.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
#ifndef __YAP_PROLOG__
static void setArgvPrologFlag(void);
#endif
static void setTZPrologFlag(void);
#ifndef __YAP_PROLOG__
static void setVersionPrologFlag(void);
#endif
static atom_t lookupAtomFlag(atom_t key);

typedef struct _prolog_flag
{ short		flags;			/* Type | Flags */
  short		index;			/* index in PLFLAG_ mask */
  union
  { atom_t	a;			/* value as atom */
    int64_t	i;			/* value as integer */
    double	f;			/* value as float */
    record_t	t;			/* value as term */
  } value;
} prolog_flag;


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
C-interface for defining Prolog  flags.  Depending   on  the  type,  the
following arguments are to be provided:

    FT_BOOL	TRUE/FALSE, *PLFLAG_
    FT_INTEGER  intptr_t
    FT_ATOM	const char *
    FT_TERM	a term
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int
indexOfBoolMask(unsigned int mask)
{ int i=1;

  if ( !mask )
    return -1;

  while(!(mask & 0x1))
  { i++;
    mask >>= 1;
  }
  return i;
}


void
setPrologFlag(const char *name, int flags, ...)
{ GET_LD
  atom_t an = PL_new_atom(name);
  prolog_flag *f;
  Symbol s;
  va_list args;
  int type = (flags & FT_MASK);

  initPrologFlagTable();

  if ( type == FT_INT64 )
    flags = (flags & ~FT_MASK)|FT_INTEGER;

  if ( (s = lookupHTable(GD->prolog_flag.table, (void *)an)) )
  { f = s->value;
    assert((f->flags & FT_MASK) == (flags & FT_MASK));
    if ( flags & FF_KEEP )
      return;
  } else
  { f = allocHeap(sizeof(*f));
    f->index = -1;
    f->flags = flags;
    addHTable(GD->prolog_flag.table, (void *)an, f);
  }

  va_start(args, flags);
  switch(type)
  { case FT_BOOL:
    { int           val = va_arg(args, int);
      unsigned int mask = va_arg(args, unsigned int);

      if ( s && mask && f->index < 0 )		/* type definition */
      { f->index = indexOfBoolMask(mask);
	val = (f->value.a == ATOM_true);
      } else if ( !s )				/* 1st definition */
      { f->index = indexOfBoolMask(mask);
	DEBUG(2, Sdprintf("Prolog flag %s at 0x%08lx\n", name, mask));
      }

      f->value.a = (val ? ATOM_true : ATOM_false);
      if ( f->index >= 0 )
      { mask = (unsigned int)1 << (f->index-1);

	if ( val )
	  setPrologFlagMask(mask);
	else
	  clearPrologFlagMask(mask);
      }
      break;
    }
    case FT_INTEGER:
    { intptr_t val = va_arg(args, intptr_t);
      f->value.i = val;
      break;
    }
    case FT_FLOAT:
    { double val = va_arg(args, double);
      f->value.f = val;
      break;
    }
    case FT_INT64:
    { int64_t val = va_arg(args, int64_t);
      f->value.i = val;
      break;
    }
    case FT_ATOM:
    { PL_chars_t text;

      text.text.t    = va_arg(args, char *);
      text.encoding  = ENC_UTF8;
      text.storage   = PL_CHARS_HEAP;
      text.length    = strlen(text.text.t);
      text.canonical = FALSE;

      f->value.a = textToAtom(&text);	/* registered: ok */
      PL_free_text(&text);

      break;
    }
    case FT_TERM:
    { term_t t = va_arg(args, term_t);

      f->value.t = PL_record(t);
      break;
    }
    default:
      assert(0);
  }
  va_end(args);
}


#ifdef O_PLMT
static void
copySymbolPrologFlagTable(Symbol s)
{ GET_LD
  prolog_flag *f = s->value;
  prolog_flag *copy = allocHeap(sizeof(*copy));

  *copy = *f;
  if ( (f->flags & FT_MASK) == FT_TERM )
    copy->value.t = PL_duplicate_record(f->value.t);
  s->value = copy;
}


static void
freeSymbolPrologFlagTable(Symbol s)
{ GET_LD
  prolog_flag *f = s->value;

  if ( (f->flags & FT_MASK) == FT_TERM )
    PL_erase(f->value.t);

  freeHeap(f, sizeof(*f));
}
#endif

#ifndef __YAP_PROLOG__
int
setDoubleQuotes(atom_t a, unsigned int *flagp)
{ GET_LD
  unsigned int flags;

  if ( a == ATOM_chars )
    flags = DBLQ_CHARS;
  else if ( a == ATOM_codes )
    flags = 0;
  else if ( a == ATOM_atom )
    flags = DBLQ_ATOM;
  else if ( a == ATOM_string )
    flags = DBLQ_STRING;
  else
  { term_t value = PL_new_term_ref();

    PL_put_atom(value, a);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN,
		    ATOM_double_quotes, value);
  }

  *flagp &= ~DBLQ_MASK;
  *flagp |= flags;

  succeed;
}


static int
setUnknown(atom_t a, unsigned int *flagp)
{ unsigned int flags;

  if ( a == ATOM_error )
    flags = UNKNOWN_ERROR;
  else if ( a == ATOM_warning )
    flags = UNKNOWN_WARNING;
  else if ( a == ATOM_fail )
    flags = UNKNOWN_FAIL;
  else
  { GET_LD
    term_t value = PL_new_term_ref();

    PL_put_atom(value, a);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_unknown, value);
  }

  *flagp &= ~(UNKNOWN_MASK);
  *flagp |= flags;

  succeed;
}


static int
setWriteAttributes(atom_t a)
{ GET_LD
  int mask = writeAttributeMask(a);

  if ( mask )
  { LD->prolog_flag.write_attributes = mask;
    succeed;
  } else
  { term_t value = PL_new_term_ref();

    PL_put_atom(value, a);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_write_attributes, value);
  }
}


static int
getOccursCheckMask(atom_t a, occurs_check_t *val)
{ if ( a == ATOM_false )
  { *val = OCCURS_CHECK_FALSE;
  } else if ( a == ATOM_true )
  { *val = OCCURS_CHECK_TRUE;
  } else if ( a == ATOM_error )
  { *val = OCCURS_CHECK_ERROR;
  } else
    fail;

  succeed;
}


static int
setOccursCheck(atom_t a)
{ GET_LD

  if ( getOccursCheckMask(a, &LD->prolog_flag.occurs_check) )
  { succeed;
  } else
  { term_t value = PL_new_term_ref();

    PL_put_atom(value, a);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_occurs_check, value);
  }
}

#endif /* __YAP_PROLOG__ */

static int
setEncoding(atom_t a)
{ GET_LD
  IOENC enc = atom_to_encoding(a);

  if ( enc == ENC_UNKNOWN )
  { term_t value = PL_new_term_ref();

    PL_put_atom(value, a);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_encoding, value);
  }

  LD->encoding = enc;

  succeed;
}


static word
set_prolog_flag_unlocked(term_t key, term_t value, int flags)
{ GET_LD
  atom_t k;
  Symbol s;
  prolog_flag *f;
  Module m = MODULE_parse;
  int rval = TRUE;

  PL_strip_module(key, &m, key);
  if ( !PL_get_atom(key, &k) )
    return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_atom, key);

					/* set existing Prolog flag */
#ifdef O_PLMT
  if ( LD->prolog_flag.table &&
       (s = lookupHTable(LD->prolog_flag.table, (void *)k)) )
  { f = s->value;			/* already local Prolog flag */
  } else
#endif
  if ( (s = lookupHTable(GD->prolog_flag.table, (void *)k)) )
  { f = s->value;
    if ( f->flags & FF_READONLY )
      return PL_error(NULL, 0, NULL, ERR_PERMISSION,
		      ATOM_modify, ATOM_flag, key);

#ifdef O_PLMT
    if ( GD->statistics.threads_created > 1 )
    { prolog_flag *f2 = allocHeap(sizeof(*f2));

      *f2 = *f;
      if ( (f2->flags & FT_MASK) == FT_TERM )
	f2->value.t = PL_duplicate_record(f2->value.t);

      if ( !LD->prolog_flag.table )
      { LD->prolog_flag.table = newHTable(4);

	LD->prolog_flag.table->copy_symbol = copySymbolPrologFlagTable;
	LD->prolog_flag.table->free_symbol = freeSymbolPrologFlagTable;
      }

      addHTable(LD->prolog_flag.table, (void *)k, f2);
      DEBUG(1, Sdprintf("Localised Prolog flag %s\n", PL_atom_chars(k)));
      f = f2;
    }
#endif
  } else if ( !(flags & FF_NOCREATE) )	/* define new Prolog flag */
  { prolog_flag *f;
    atom_t a;
    int64_t i;
    double d;

  anyway:
    PL_register_atom(k);
    f = allocHeap(sizeof(*f));
    f->index = -1;

    switch( (flags & FT_MASK) )
    { case FT_FROM_VALUE:
      { if ( PL_get_atom(value, &a) )
	{ if ( a == ATOM_true || a == ATOM_false ||
	       a == ATOM_on || a == ATOM_off )
	    f->flags = FT_BOOL;
	  else
	    f->flags = FT_ATOM;
	  f->value.a = a;
	  PL_register_atom(a);
	} else if ( PL_get_int64(value, &i) )
	{ f->flags = FT_INTEGER;
	  f->value.i = i;
	} else if ( PL_get_float(value, &d) )
	{ f->flags = FT_FLOAT;
	  f->value.f = d;
	} else
	{ f->flags = FT_TERM;
	  if ( !PL_is_ground(value) )
	  { PL_error(NULL, 0, NULL, ERR_INSTANTIATION);
	    goto wrong_type;
	  }
	  if ( !(f->value.t = PL_record(value)) )
	    goto wrong_type;
	  f->value.t = PL_record(value);
	}
	break;
      }
      case FT_ATOM:
	if ( !PL_get_atom_ex(value, &f->value.a) )
	{ wrong_type:
	  freeHeap(f, sizeof(*f));
	  return FALSE;
	}
        f->flags = FT_ATOM;
        PL_register_atom(f->value.a);
	break;
      case FT_BOOL:
      { int b;
	if ( !PL_get_bool_ex(value, &b) )
	  goto wrong_type;
        f->flags = FT_BOOL;
	f->value.a = (b ? ATOM_true : ATOM_false);
	break;
      }
      case FT_INTEGER:
	if ( !PL_get_int64_ex(value, &f->value.i) )
	  goto wrong_type;
        f->flags = FT_INTEGER;
	break;
      case FT_FLOAT:
	if ( !PL_get_float_ex(value, &f->value.f) )
	  goto wrong_type;
        f->flags = FT_FLOAT;
	break;
      case FT_TERM:
	if ( !PL_is_ground(value) )
	{ PL_error(NULL, 0, NULL, ERR_INSTANTIATION);
	  goto wrong_type;
	}
        if ( !(f->value.t = PL_record(value)) )
	  goto wrong_type;
        f->flags = FT_TERM;
	break;
    }

    if ( (flags & FF_READONLY) )
      f->flags |= FF_READONLY;

    addHTable(GD->prolog_flag.table, (void *)k, f);

    succeed;
  } else
  { atom_t how = lookupAtomFlag(ATOM_user_flags);

    if ( how == ATOM_error )
      return PL_error(NULL, 0, NULL, ERR_EXISTENCE,
		      ATOM_prolog_flag, key);
    else if ( how == ATOM_warning )
      Sdprintf("WARNING: Flag %s: new Prolog flags must be created using "
	       "create_prolog_flag/3\n", stringAtom(k));

    goto anyway;
  }

  switch(f->flags & FT_MASK)
  { case FT_BOOL:
    { int val;

      if ( !PL_get_bool_ex(value, &val) )
	return FALSE;
      if ( f->index > 0 )
      { unsigned int mask = (unsigned int)1 << (f->index-1);

	if ( val )
	  setPrologFlagMask(mask);
	else
	  clearPrologFlagMask(mask);
      }
#ifndef __YAP_PROLOG__
      if ( k == ATOM_character_escapes )
      { if ( val )
	  set(m, CHARESCAPE);
	else
	  clear(m, CHARESCAPE);
      } else if ( k == ATOM_debug )
      { if ( val )
	{ debugmode(DBG_ALL, NULL);
	} else
	{ tracemode(FALSE, NULL);
	  debugmode(DBG_OFF, NULL);
	}
      } else if ( k == ATOM_debugger_show_context )
      { debugstatus.showContext = val;
#ifdef O_PLMT
      } else if ( k == ATOM_threads )
      { if ( !(rval = enableThreads(val)) )
	  break;			/* don't change value */
#endif
      }
#endif /* __YAP_PROLOG__ */

					/* set the flag value */
      f->value.a = (val ? ATOM_true : ATOM_false);

      break;
    }
    case FT_ATOM:
    { atom_t a;

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

#ifndef __YAP_PROLOG__
      if ( k == ATOM_double_quotes )
      { rval = setDoubleQuotes(a, &m->flags);
      } else if ( k == ATOM_unknown )
      { rval = setUnknown(a, &m->flags);
      } else if ( k == ATOM_write_attributes )
      { rval = setWriteAttributes(a);
      } else if ( k == ATOM_occurs_check )
      { rval = setOccursCheck(a);
      } else 
#endif
      if ( k == ATOM_encoding )
      { rval = setEncoding(a);
      }
      if ( !rval )
	fail;

      PL_unregister_atom(f->value.a);
      f->value.a = a;
      PL_register_atom(a);
      break;
    }
    case FT_INTEGER:
    { int64_t i;

      if ( !PL_get_int64_ex(value, &i) )
	return FALSE;
      f->value.i = i;
#ifdef O_ATOMGC
      if ( k == ATOM_agc_margin )
	GD->atoms.margin = (size_t)i;
#endif
      break;
    }
    case FT_FLOAT:
    { double d;

      if ( !PL_get_float_ex(value, &d) )
	return FALSE;
      f->value.f = d;
      break;
    }
    case FT_TERM:
    { if ( f->value.t )
	PL_erase(f->value.t);
      f->value.t = PL_record(value);
      break;
    }
    default:
      assert(0);
  }

  return rval;
}


/** set_prolog_flag(+Key, +Value) is det.
*/

static
PRED_IMPL("set_prolog_flag", 2, set_prolog_flag, PL_FA_ISO)
{ word rc;

  LOCK();
  rc = set_prolog_flag_unlocked(A1, A2, FF_NOCREATE|FT_FROM_VALUE);
  UNLOCK();

  return rc;
}


/** create_prolog_flag(+Key, +Value, +Options) is det.
*/

static const opt_spec prolog_flag_options[] =
{ { ATOM_type,   OPT_ATOM },
  { ATOM_access, OPT_ATOM },
  { NULL_ATOM,   0 }
};

static
PRED_IMPL("create_prolog_flag", 3, create_prolog_flag, PL_FA_ISO)
{ PRED_LD
  word rc;
  int flags = 0;
  atom_t type = 0;
  atom_t access = ATOM_read_write;

  if ( !scan_options(A3, 0, ATOM_prolog_flag_option, prolog_flag_options,
		     &type, &access) )
    return FALSE;

  if ( type == 0 )
    flags |= FT_FROM_VALUE;
  else if ( type == ATOM_boolean )
    flags |= FT_BOOL;
  else if ( type == ATOM_integer )
    flags |= FT_INTEGER;
  else if ( type == ATOM_float )
    flags |= FT_FLOAT;
  else if ( type == ATOM_atom )
    flags |= FT_ATOM;
  else if ( type == ATOM_term )
    flags |= FT_TERM;
  else
  { term_t a = PL_new_term_ref();
    PL_put_atom(a, type);

    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_prolog_flag_type, a);
  }

  if ( access == ATOM_read_only )
    flags |= FF_READONLY;
  else if ( access != ATOM_read_write )
  { term_t a = PL_new_term_ref();
    PL_put_atom(a, access);
    return PL_error(NULL, 0, NULL, ERR_DOMAIN, ATOM_prolog_flag_access, a);
  }

  LOCK();
  rc = set_prolog_flag_unlocked(A1, A2, flags);
  UNLOCK();

  return rc;
}


static atom_t
lookupAtomFlag(atom_t key)
{ GET_LD
  Symbol s;
  prolog_flag *f = NULL;

#ifdef O_PLMT
  if ( LD->prolog_flag.table &&
       (s = lookupHTable(LD->prolog_flag.table, (void *)key)) )
  { f = s->value;
  } else
#endif
  { if ( (s = lookupHTable(GD->prolog_flag.table, (void *)key)) )
      f = s->value;
  }

  if ( f )
  { assert((f->flags&FT_MASK) == FT_ATOM);
    return f->value.a;
  }

  return NULL_ATOM;
}


static int
unify_prolog_flag_value(Module m, atom_t key, prolog_flag *f, term_t val)
{ GET_LD

#ifndef __YAP_PROLOG__
  if ( key == ATOM_character_escapes )
  { atom_t v = (true(m, CHARESCAPE) ? ATOM_true : ATOM_false);

    return PL_unify_atom(val, v);
  } else if ( key == ATOM_double_quotes )
  { atom_t v;

    if ( true(m, DBLQ_CHARS) )
      v = ATOM_chars;
    else if ( true(m, DBLQ_ATOM) )
      v = ATOM_atom;
    else if ( true(m, DBLQ_STRING) )
      v = ATOM_string;
    else
      v = ATOM_codes;

    return PL_unify_atom(val, v);
  } else if ( key == ATOM_unknown )
  { atom_t v;

    switch ( getUnknownModule(m) )
    { case UNKNOWN_ERROR:
	v = ATOM_error;
        break;
      case UNKNOWN_WARNING:
	v = ATOM_warning;
        break;
      case UNKNOWN_FAIL:
	v = ATOM_fail;
        break;
      default:
	assert(0);
    }

    return PL_unify_atom(val, v);
#ifdef O_PLMT
  } else if ( key == ATOM_system_thread_id )
  { return PL_unify_integer(val, system_thread_id(NULL));
#endif
  } else if ( key == ATOM_debug )
  { return PL_unify_bool_ex(val, debugstatus.debugging);
  } else if ( key == ATOM_debugger_show_context )
  { return PL_unify_bool_ex(val, debugstatus.showContext);
  }
#endif /* YAP_PROLOG */

  switch(f->flags & FT_MASK)
  { case FT_BOOL:
      if ( f->index >= 0 )
      { unsigned int mask = (unsigned int)1 << (f->index-1);

	return PL_unify_bool_ex(val, truePrologFlag(mask) != FALSE);
      }
      /*FALLTHROUGH*/
    case FT_ATOM:
      return PL_unify_atom(val, f->value.a);
    case FT_INTEGER:
      return PL_unify_int64(val, f->value.i);
    case FT_FLOAT:
      return PL_unify_float(val, f->value.f);
    case FT_TERM:
    { term_t tmp = PL_new_term_ref();

      if ( PL_recorded(f->value.t, tmp) )
	return PL_unify(val, tmp);
      else
	return raiseStackOverflow(GLOBAL_OVERFLOW);
    }
    default:
      assert(0);
      fail;
  }
}


static int
unify_prolog_flag_access(prolog_flag *f, term_t access)
{ GET_LD

  if ( f->flags & FF_READONLY )
    return PL_unify_atom(access, ATOM_read);
  else
    return PL_unify_atom(access, ATOM_write);
}


static int
unify_prolog_flag_type(prolog_flag *f, term_t type)
{ GET_LD
  atom_t a;

  switch(f->flags & FT_MASK)
  { case FT_BOOL:
      a = ATOM_boolean;
      break;
    case FT_ATOM:
      a = ATOM_atom;
      break;
    case FT_INTEGER:
      a = ATOM_integer;
      break;
    case FT_FLOAT:
      a = ATOM_float;
      break;
    case FT_TERM:
      a = ATOM_term;
      break;
    default:
      assert(0);
      fail;
  }

  return PL_unify_atom(type, a);
}


typedef struct
{ TableEnum table_enum;
  atom_t scope;
  int explicit_scope;
  Module module;
} prolog_flag_enum;

word
pl_prolog_flag5(term_t key, term_t value,
	    word scope, word access, word type,
	    control_t h)
{ GET_LD
  prolog_flag_enum *e;
  Symbol s;
  fid_t fid;
  Module module;

  switch( ForeignControl(h) )
  { case FRG_FIRST_CALL:
    { atom_t k;

      module = MODULE_parse;
      PL_strip_module(key, &module, key);

      if ( PL_get_atom(key, &k) )
      { Symbol s;

#ifdef O_PLMT
	if ( LD->prolog_flag.table &&
	     (s = lookupHTable(LD->prolog_flag.table, (void *)k)) )
	  return unify_prolog_flag_value(module, k, s->value, value);
#endif
	if ( (s = lookupHTable(GD->prolog_flag.table, (void *)k)) )
	{ if ( unify_prolog_flag_value(module, k, s->value, value) &&
	       (!access || unify_prolog_flag_access(s->value, access)) &&
	       (!type   || unify_prolog_flag_type(s->value, type)) )
	    succeed;
	}

	fail;
      } else if ( PL_is_variable(key) )
      { e = allocHeap(sizeof(*e));

	e->module = module;

	if ( scope && PL_get_atom(scope, &e->scope) )
	{ e->explicit_scope = TRUE;
	  if ( !(e->scope == ATOM_local || e->scope == ATOM_global) )
	  { freeHeap(e, sizeof(*e));
	    return PL_error(NULL, 0, NULL, ERR_DOMAIN,
			    PL_new_atom("scope"), scope);
	  }
	} else
	{ e->explicit_scope = FALSE;

	  if ( LD->prolog_flag.table )
	    e->scope = ATOM_local;
	  else
	    e->scope = ATOM_global;
	}

	if ( e->scope == ATOM_local )
	  e->table_enum = newTableEnum(LD->prolog_flag.table);
	else
	  e->table_enum = newTableEnum(GD->prolog_flag.table);

	break;
      } else
	return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_atom, key);
    }
    case FRG_REDO:
      e = ForeignContextPtr(h);
      break;
    case FRG_CUTTED:
      e = ForeignContextPtr(h);
      if ( e )
      { freeTableEnum(e->table_enum);
	freeHeap(e, sizeof(*e));
      }
    default:
      succeed;
  }

  fid = PL_open_foreign_frame();
  LOCK();
  for(;;)
  { while( (s=advanceTableEnum(e->table_enum)) )
    { atom_t fn = (atom_t) s->name;

      if ( e->explicit_scope == FALSE &&
	   e->scope == ATOM_global &&
	   LD->prolog_flag.table &&
	   lookupHTable(LD->prolog_flag.table, (void *)fn) )
	continue;

      if ( PL_unify_atom(key, fn) &&
	   unify_prolog_flag_value(e->module, fn, s->value, value) &&
	   (!scope  || PL_unify_atom(scope, e->scope)) &&
	   (!access || unify_prolog_flag_access(s->value, access)) &&
	   (!type   || unify_prolog_flag_type(s->value, type)) )
      { UNLOCK();
	ForeignRedoPtr(e);
      }
#ifndef __YAP_PROLOG__
      if ( exception_term )
      { exception_term = 0;
	setVar(*valTermRef(exception_bin));
      }
#endif
      PL_rewind_foreign_frame(fid);
    }

    if ( e->scope == ATOM_local )
    { e->scope = ATOM_global;
      freeTableEnum(e->table_enum);
      e->table_enum = newTableEnum(GD->prolog_flag.table);
    } else
      break;
  }
  UNLOCK();

  freeTableEnum(e->table_enum);
  freeHeap(e, sizeof(*e));

  fail;
}


foreign_t
pl_prolog_flag(term_t name, term_t value, control_t h)
{ return pl_prolog_flag5(name, value, 0, 0, 0, h);
}


		 /*******************************
		 *	INITIALISE FEATURES	*
		 *******************************/

#ifndef SO_EXT
#define SO_EXT "so"
#endif
#ifndef SO_PATH
#define SO_PATH "LD_LIBRARY_PATH"
#endif

void
initPrologFlagTable(void)
{ if ( !GD->prolog_flag.table )
  { 
#ifndef __YAP_PROLOG__
    initPrologThreads();	/* may be called before PL_initialise() */
#endif

    GD->prolog_flag.table = newHTable(32);
  }
}


void
initPrologFlags(void)
{ GET_LD
#ifndef __YAP_PROLOG__
  setPrologFlag("iso",  FT_BOOL, FALSE, PLFLAG_ISO);
  setPrologFlag("arch", FT_ATOM|FF_READONLY, ARCH);
#if __WINDOWS__
  setPrologFlag("windows",	FT_BOOL|FF_READONLY, TRUE, 0);
#endif
  setPrologFlag("version",	FT_INTEGER|FF_READONLY, PLVERSION);
  setPrologFlag("dialect", FT_ATOM|FF_READONLY, "swi");
  if ( systemDefaults.home )
    setPrologFlag("home", FT_ATOM|FF_READONLY, systemDefaults.home);
  if ( GD->paths.executable )
    setPrologFlag("executable", FT_ATOM|FF_READONLY, GD->paths.executable);
#if defined(HAVE_GETPID) || defined(EMULATE_GETPID)
  setPrologFlag("pid", FT_INTEGER|FF_READONLY, getpid());
#endif
  setPrologFlag("generate_debug_info", FT_BOOL,
	     truePrologFlag(PLFLAG_DEBUGINFO), PLFLAG_DEBUGINFO);
  setPrologFlag("last_call_optimisation", FT_BOOL, TRUE, PLFLAG_LASTCALL);
  setPrologFlag("c_libs",	  FT_ATOM|FF_READONLY, C_LIBS);
  setPrologFlag("c_cc",	  FT_ATOM|FF_READONLY, C_CC);
  setPrologFlag("c_ldflags", FT_ATOM|FF_READONLY, C_LDFLAGS);
#if defined(O_LARGEFILES) || SIZEOF_LONG == 8
  setPrologFlag("large_files", FT_BOOL|FF_READONLY, TRUE, 0);
#endif
  setPrologFlag("gc",	  FT_BOOL,	       TRUE,  PLFLAG_GC);
  setPrologFlag("trace_gc",  FT_BOOL,	       FALSE, PLFLAG_TRACE_GC);
#ifdef O_ATOMGC
  setPrologFlag("agc_margin",FT_INTEGER,	       GD->atoms.margin);
#endif
#if defined(HAVE_DLOPEN) || defined(HAVE_SHL_LOAD) || defined(EMULATE_DLOPEN)
  setPrologFlag("open_shared_object",	  FT_BOOL|FF_READONLY, TRUE, 0);
  setPrologFlag("shared_object_extension",	  FT_ATOM|FF_READONLY, SO_EXT);
  setPrologFlag("shared_object_search_path", FT_ATOM|FF_READONLY, SO_PATH);
#endif
  setPrologFlag("address_bits", FT_INTEGER|FF_READONLY, sizeof(void*)*8);
#ifdef HAVE_POPEN
  setPrologFlag("pipe", FT_BOOL, TRUE, 0);
#endif
#ifdef O_PLMT
  setPrologFlag("threads",	FT_BOOL|FF_READONLY, TRUE, 0);
  setPrologFlag("system_thread_id", FT_INTEGER|FF_READONLY, 0, 0);
#else
  setPrologFlag("threads",	FT_BOOL|FF_READONLY, FALSE, 0);
#endif
#ifdef ASSOCIATE_SRC
  setPrologFlag("associate", FT_ATOM, ASSOCIATE_SRC);
#endif
#ifdef O_DDE
  setPrologFlag("dde", FT_BOOL|FF_READONLY, TRUE, 0);
#endif
#ifdef O_RUNTIME
  setPrologFlag("runtime",	FT_BOOL|FF_READONLY, TRUE, 0);
  setPrologFlag("debug_on_error", FT_BOOL|FF_READONLY, FALSE,
	     PLFLAG_DEBUG_ON_ERROR);
  setPrologFlag("report_error",	FT_BOOL|FF_READONLY, FALSE,
	     PLFLAG_REPORT_ERROR);
#else
  setPrologFlag("debug_on_error",	FT_BOOL, TRUE, PLFLAG_DEBUG_ON_ERROR);
  setPrologFlag("report_error",	FT_BOOL, TRUE, PLFLAG_REPORT_ERROR);
#endif
  setPrologFlag("user_flags", FT_ATOM, "silent");
  setPrologFlag("editor", FT_ATOM, "default");
  setPrologFlag("debugger_show_context", FT_BOOL, FALSE, 0);
  setPrologFlag("autoload",  FT_BOOL, TRUE,  PLFLAG_AUTOLOAD);
#ifndef O_GMP
  setPrologFlag("max_integer",	   FT_INT64|FF_READONLY, PLMAXINT);
  setPrologFlag("min_integer",	   FT_INT64|FF_READONLY, PLMININT);
#endif
  setPrologFlag("max_tagged_integer", FT_INTEGER|FF_READONLY, PLMAXTAGGEDINT);
  setPrologFlag("min_tagged_integer", FT_INTEGER|FF_READONLY, PLMINTAGGEDINT);
#ifdef O_GMP
  setPrologFlag("bounded",		   FT_BOOL|FF_READONLY,	   FALSE, 0);
#ifdef __GNU_MP__
  setPrologFlag("gmp_version",	   FT_INTEGER|FF_READONLY, __GNU_MP__);
#endif
#else
  setPrologFlag("bounded",		   FT_BOOL|FF_READONLY,	   TRUE, 0);
#endif
  if ( (-3 / 2) == -2 )
    setPrologFlag("integer_rounding_function", FT_ATOM|FF_READONLY, "down");
  else
    setPrologFlag("integer_rounding_function", FT_ATOM|FF_READONLY, "toward_zero");
  setPrologFlag("max_arity", FT_ATOM|FF_READONLY, "unbounded");
  setPrologFlag("answer_format", FT_ATOM, "~p");
  setPrologFlag("character_escapes", FT_BOOL, TRUE, PLFLAG_CHARESCAPE);
  setPrologFlag("char_conversion", FT_BOOL, FALSE, PLFLAG_CHARCONVERSION);
  setPrologFlag("backquoted_string", FT_BOOL, FALSE, PLFLAG_BACKQUOTED_STRING);
  setPrologFlag("write_attributes", FT_ATOM, "ignore");
  setPrologFlag("occurs_check", FT_ATOM, "false");
  setPrologFlag("double_quotes", FT_ATOM, "codes");
  setPrologFlag("unknown", FT_ATOM, "error");
  setPrologFlag("debug", FT_BOOL, FALSE, 0);
  setPrologFlag("verbose", FT_ATOM|FF_KEEP, GD->options.silent ? "silent" : "normal");
  setPrologFlag("verbose_load", FT_BOOL, TRUE, 0);
  setPrologFlag("verbose_autoload", FT_BOOL, FALSE, 0);
  setPrologFlag("verbose_file_search", FT_BOOL, FALSE, 0);
  setPrologFlag("allow_variable_name_as_functor", FT_BOOL, FALSE,
	     ALLOW_VARNAME_FUNCTOR);
  setPrologFlag("toplevel_var_size", FT_INTEGER, 1000);
  setPrologFlag("toplevel_print_anon", FT_BOOL, TRUE, 0);
#ifdef __unix__
  setPrologFlag("unix", FT_BOOL|FF_READONLY, TRUE, 0);
#endif

  setPrologFlag("signals", FT_BOOL|FF_READONLY,
	     truePrologFlag(PLFLAG_SIGNALS), PLFLAG_SIGNALS);

#if defined(__WINDOWS__) && defined(_DEBUG)
  setPrologFlag("kernel_compile_mode", FT_ATOM|FF_READONLY, "debug");
#endif

#if defined(__DATE__) && defined(__TIME__)
  { char buf[100];

    Ssprintf(buf, "%s, %s", __DATE__, __TIME__);
    setPrologFlag("compiled_at", FT_ATOM|FF_READONLY, buf);
  }
#endif
#endif /* YAP_PROLOG */
  /* Flags copied by YAP */
  setPrologFlag("optimise", FT_BOOL, GD->cmdline.optimise, PLFLAG_OPTIMISE);
  /* FLAGS used by PLStream */
  setPrologFlag("tty_control", FT_BOOL|FF_READONLY,
	     truePrologFlag(PLFLAG_TTY_CONTROL), PLFLAG_TTY_CONTROL);
  setPrologFlag("encoding", FT_ATOM, stringAtom(encoding_to_atom(LD->encoding)));
  setPrologFlag("file_name_variables", FT_BOOL, FALSE, PLFLAG_FILEVARS);
  setPrologFlag("fileerrors", FT_BOOL, TRUE, PLFLAG_FILEERRORS);
  setPrologFlag("readline", FT_BOOL/*|FF_READONLY*/, FALSE, 0);


#ifndef __YAP_PROLOG__
  setArgvPrologFlag();
#endif /* YAP_PROLOG */
  setTZPrologFlag();
#ifndef __YAP_PROLOG__
  setOSPrologFlags();
  setVersionPrologFlag();
#endif /* YAP_PROLOG */
}


#ifndef __YAP_PROLOG__
static void
setArgvPrologFlag()
{ GET_LD
  fid_t fid = PL_open_foreign_frame();
  term_t e = PL_new_term_ref();
  term_t l = PL_new_term_ref();
  int argc    = GD->cmdline.argc;
  char **argv = GD->cmdline.argv;
  int n;

  PL_put_nil(l);
  for(n=argc-1; n>= 0; n--)
  { PL_put_variable(e);
    if ( !PL_unify_chars(e, PL_ATOM|REP_FN, -1, argv[n]) ||
	 !PL_cons_list(l, e, l) )
      fatalError("Could not set Prolog flag argv: not enough stack");
  }

  setPrologFlag("argv", FT_TERM, l);
  PL_discard_foreign_frame(fid);
}

#endif

static void
setTZPrologFlag()
{ tzset();

  setPrologFlag("timezone", FT_INTEGER|FF_READONLY, timezone);
}

#ifndef __YAP_PROLOG__

static void
setVersionPrologFlag(void)
{ GET_LD
  fid_t fid = PL_open_foreign_frame();
  term_t t = PL_new_term_ref();
  int major = PLVERSION/10000;
  int minor = (PLVERSION/100)%100;
  int patch = (PLVERSION%100);

  if ( !PL_unify_term(t,
		      PL_FUNCTOR_CHARS, "swi", 4,
		        PL_INT, major,
		        PL_INT, minor,
		        PL_INT, patch,
		        PL_ATOM, ATOM_nil) )
    sysError("Could not set version");

  setPrologFlag("version_data", FF_READONLY|FT_TERM, t);
  PL_discard_foreign_frame(fid);

  setGITVersion();
}
#endif /* YAP_PROLOG */
		 /*******************************
		 *      PUBLISH PREDICATES	*
		 *******************************/

BeginPredDefs(prologflag)
  PRED_DEF("$swi_set_prolog_flag",    2, set_prolog_flag,    PL_FA_ISO)
  PRED_DEF("$swi_create_prolog_flag", 3, create_prolog_flag, 0)
EndPredDefs