File: pl-supervisor.c

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/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemak@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (C): 2006-2012, University of Amsterdam
			      VU University Amsterdam

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

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

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

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

#define MAX_FLI_ARGS 10			/* extend switches on change */

static Code
allocCodes(size_t n)
{ Code codes = allocHeapOrHalt(sizeof(code)*(n+1));

  *codes++ = (code)n;

  return codes;
}


static void
freeCodes(Code codes)
{ size_t size = (size_t)codes[-1];

  if ( size > 0 )		/* 0: built-in, see initSupervisors() */
    freeHeap(&codes[-1], (size+1)*sizeof(code));
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
freeCodesDefinition() destroys the supervisor of  a predicate, replacing
it  by  the  statically  allocated  S_VIRGIN  supervisor.  Note  that  a
predicate *always* has non-NULL def->codes.

If linger == FALSE, we  are  absolutely   sure  that  it  is harmless to
deallocate the old supervisor. If TRUE,   there may be references. I.e.,
other threads may have started executing this predicate.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

void
freeCodesDefinition(Definition def, int linger)
{ Code codes;

  if ( (codes=def->codes) != SUPERVISOR(virgin) )
  { if ( (codes = def->codes) )
    { size_t size = (size_t)codes[-1];

      def->codes = SUPERVISOR(virgin);
      if ( size > 0 )		/* 0: built-in, see initSupervisors() */
      { if ( linger )
	  PL_linger(&codes[-1]);
	else
	  freeHeap(&codes[-1], (size+1)*sizeof(code));
      }
    } else
      def->codes = SUPERVISOR(virgin);
  }
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Foreign supervisors.  Creates one of:

DET code:  I_FOPEN,     I_FCALLDETVA|I_FCALLDET<N>,   I_FEXITDET
NDET code: I_FOPENNDET, I_FCALLNDETVA|I_FCALLNDET<N>, I_FEXITNDET, I_FREDO
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

#ifdef O_PROF_PENTIUM
#include "pentium.h"
static int prof_foreign_index = (I_HIGHEST+20);
#endif

int
createForeignSupervisor(Definition def, Func f)
{ assert(true(def, P_FOREIGN));

  if ( false(def, P_VARARG) )
  { if ( def->functor->arity > MAX_FLI_ARGS )
      sysError("Too many arguments to foreign function %s (>%d)", \
	       predicateName(def), MAX_FLI_ARGS); \
  }

  if ( false(def, P_NONDET) )
  { Code codes = allocCodes(4);

    codes[0] = encode(I_FOPEN);
    if ( true(def, P_VARARG) )
      codes[1] = encode(I_FCALLDETVA);
    else
      codes[1] = encode(I_FCALLDET0+def->functor->arity);
    codes[2] = (code)f;
    codes[3] = encode(I_FEXITDET);

    def->codes = codes;
  } else
  { Code codes = allocCodes(5);

    codes[0] = encode(I_FOPENNDET);
    if ( true(def, P_VARARG) )
      codes[1] = encode(I_FCALLNDETVA);
    else
      codes[1] = encode(I_FCALLNDET0+def->functor->arity);
    codes[2] = (code)f;
    codes[3] = encode(I_FEXITNDET);
    codes[4] = encode(I_FREDO);

    def->codes = codes;
  }

#ifdef O_PROF_PENTIUM
  assert(prof_foreign_index < MAXPROF);
  def->prof_index = prof_foreign_index++;
  def->prof_name  = strdup(predicateName(def));
#endif

  succeed;
}


		 /*******************************
		 *	   PROLOG CASES		*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
getClauses() finds alive clauses and stores them into the array refp. It
stores at most `max' clauses and returns   the total number of candidate
clauses. This code is only executed on   static code and in theory there
should be no reason to validate the  counts, but reconsulting files must
make us careful.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static int
getClauses(Definition def, ClauseRef *refp, int max)
{ ClauseRef cref;
  int found = 0;

  for(cref = def->impl.clauses.first_clause; cref; cref = cref->next)
  { if ( visibleClause(cref->value.clause, GD->generation) )
    { if ( found < max )
	refp[found] = cref;
      found++;
    }
  }

  return found;
}


static Code
undefSupervisor(Definition def)
{ if ( def->impl.clauses.number_of_clauses == 0 && false(def, PROC_DEFINED) )
    return SUPERVISOR(undef);

  return NULL;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
createSingleClauseSupervisor() creates a supervisor to call the one and
only clause of the predicate.  Creates

	S_TRUSTME <ClauseRef>
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static Code
singleClauseSupervisor(Definition def)
{ if ( def->impl.clauses.number_of_clauses == 1 )
  { ClauseRef cref;
    Code codes = allocCodes(2);
    int found = getClauses(def, &cref, 1);

    if ( found == 1 )
    { DEBUG(1, Sdprintf("Single clause supervisor for %s\n",
			predicateName(def)));

      codes[0] = encode(S_TRUSTME);
      codes[1] = (code)cref;

      return codes;
    }
  }

  return NULL;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
createListSuperVisor() creates a supervisor for predicates that have two
clauses (possibly swapped):

	pred([], ....)
	pred([H|T], ...)

The code is

	S_LIST <nilclause> <listclause>
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static Code
listSupervisor(Definition def)
{ if ( def->impl.clauses.number_of_clauses == 2 )
  { ClauseRef cref[2];
    word c[2];
    int found = getClauses(def, cref, 2);

    if ( found == 2 &&
	 arg1Key(cref[0]->value.clause->codes, &c[0]) &&
	 arg1Key(cref[1]->value.clause->codes, &c[1]) &&
	 ( (c[0] == ATOM_nil && c[1] == FUNCTOR_dot2) ||
	   (c[1] == ATOM_nil && c[0] == FUNCTOR_dot2) ) )
    { Code codes = allocCodes(3);

      DEBUG(1, Sdprintf("List supervisor for %s\n", predicateName(def)));

      codes[0] = encode(S_LIST);
      if ( c[0] == ATOM_nil )
      { codes[1] = (code)cref[0];
	codes[2] = (code)cref[1];
      } else
      { codes[1] = (code)cref[1];
	codes[2] = (code)cref[0];
      }

      return codes;
    }
  }

  return NULL;
}


static Code
multifileSupervisor(Definition def)
{ if ( true(def, (P_DYNAMIC|P_MULTIFILE)) )
  { if ( true(def, P_DYNAMIC) )
      return SUPERVISOR(dynamic);
    else
      return SUPERVISOR(multifile);
  }

  return NULL;
}


static Code
staticSupervisor(Definition def)
{ (void)def;

  return SUPERVISOR(staticp);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Prepend the already provided  supervisor   with  code  for meta-argument
module qualifications.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static void
copySuperVisorCode(Buffer buf, Code add)
{ size_t len = supervisorLength(add);

  addMultipleBuffer(buf, add, len, code);
}


static void
copyCodes(Code dest, Code src, size_t count)
{ memcpy(dest, src, count*sizeof(code));
}


static Code
chainMetaPredicateSupervisor(Definition def, Code post)
{ if ( true(def, P_META) && true(def, P_TRANSPARENT) )
  { tmp_buffer buf;
    unsigned int i;
    int count = 0;
    Code codes;

    initBuffer(&buf);
    for(i=0; i < def->functor->arity; i++)
    { int ma = MA_INFO(def, i);

      if ( ma <= 9 || ma == MA_META || ma == MA_HAT || ma == MA_DCG ) /* 0..9, :, ^ or // */
      { addBuffer(&buf, encode(S_MQUAL), code);
	addBuffer(&buf, VAROFFSET(i), code);
	count++;
      }
    }

    if ( count > 0 )
    { baseBuffer(&buf, code)[(count-1)*2] = encode(S_LMQUAL);

      copySuperVisorCode((Buffer)&buf, post);
      freeCodes(post);
      codes = allocCodes(entriesBuffer(&buf, code));
      copyCodes(codes, baseBuffer(&buf, code), entriesBuffer(&buf, code));

      return codes;
    } else
    { discardBuffer(&buf);
    }
  }

  return post;
}


		 /*******************************
		 *	      ENTRIES		*
		 *******************************/

int
createUndefSupervisor(Definition def)
{ Code codes;

  if ( (codes = undefSupervisor(def)) )
  { def->codes = codes;

    return TRUE;
  }

  return FALSE;
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
createSupervisor()  is  synchronised  with  unloadFile()  (reconsult/1).
Seems this is not yet enough to   stop all racer conditions between this
code.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

int
createSupervisor(Definition def)
{ Code codes;
  int has_codes;

  PL_LOCK(L_PREDICATE);
  has_codes = ((codes = undefSupervisor(def)) ||
	       (codes = multifileSupervisor(def)) ||
	       (codes = singleClauseSupervisor(def)) ||
	       (codes = listSupervisor(def)) ||
	       (codes = staticSupervisor(def)));
  assert(has_codes);
  def->codes = chainMetaPredicateSupervisor(def, codes);
  PL_UNLOCK(L_PREDICATE);

  succeed;
}


		 /*******************************
		 *	      INFO		*
		 *******************************/

size_t
supervisorLength(Code base)
{ Code PC = base;
  size_t len = (size_t)base[-1];

  if ( len != 0 )
  { return len;
  } else
  { for(; decode(*PC) != I_EXIT; PC = stepPC(PC))
      ;
    PC++;					/* include I_EXIT */
    return PC-base;
  }
}


		 /*******************************
		 *	       INIT		*
		 *******************************/

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Generic and reusable code-sequences. The  entry-point of these sequences
must be accessed as:

	SUPERVISOR(name)

The code sequence starts with 0 to   avoid freeing using freeCodes(). It
ends in I_EXIT, such that generic code  walkers will always find the end
of the sequence.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

#define MAKE_SV1(name, i) { PL_code_data.supervisors.name[0] = (code)0; \
			    PL_code_data.supervisors.name[1] = encode(i); \
			    PL_code_data.supervisors.name[2] = encode(I_EXIT); \
			  }

void
initSupervisors(void)
{ MAKE_SV1(exit,	 I_EXIT);
  MAKE_SV1(next_clause,	 S_NEXTCLAUSE);
  MAKE_SV1(virgin,	 S_VIRGIN);
  MAKE_SV1(undef,	 S_UNDEF);
  MAKE_SV1(dynamic,      S_DYNAMIC);
  MAKE_SV1(thread_local, S_THREAD_LOCAL);
  MAKE_SV1(multifile,    S_MULTIFILE);
  MAKE_SV1(staticp,      S_STATIC);
}