/* -*-C-*-

$Id: future.c,v 9.33 2007/01/05 21:19:25 cph Exp $

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme 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
General Public License for more details.

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

*/

/* Support code for futures */

#include "scheme.h"
#include "prims.h"
#include "locks.h"

#ifndef COMPILE_FUTURES
#include "Error: future.c is useless without COMPILE_FUTURES"
#endif

/* This is how we support future numbering for external metering */
#ifndef New_Future_Number
#define New_Future_Number() SHARP_F
#else
SCHEME_OBJECT Get_New_Future_Number ();
#endif

/*

A future is a VECTOR starting with <determined?>, <locked?> and
<waiting queue / value>,

where <determined?> is #!false if no value is known yet,
                       #!true if value is known and future can vanish at GC,
                       otherwise value is known, but keep the slot

and where <locked> is #!true if someone wants slot kept for a time.

*/

DEFINE_PRIMITIVE ("TOUCH", Prim_touch, 1, 1, 0)
{
  SCHEME_OBJECT result;
  PRIMITIVE_HEADER (1);
  TOUCH_IN_PRIMITIVE ((ARG_REF (1)), result);
  PRIMITIVE_RETURN (result);
}

DEFINE_PRIMITIVE ("FUTURE?", Prim_future_p, 1, 1, 0)
{
  PRIMITIVE_HEADER (1);
  PRIMITIVE_RETURN (BOOLEAN_TO_OBJECT (FUTURE_P (ARG_REF (1))));
}

/* Utility setting routine for use by the various test and set if
   equal operators.
*/

long
Set_If_Equal(Base, Offset, New, Wanted)
     SCHEME_OBJECT Base, Wanted, New;
     long Offset;
{
  Lock_Handle lock;
  SCHEME_OBJECT Old_Value, Desired, Remember_Value;
  long success;

  TOUCH_IN_PRIMITIVE(Wanted, Desired);
Try_Again:
  Remember_Value = MEMORY_REF (Base, Offset);
  TOUCH_IN_PRIMITIVE(Remember_Value, Old_Value);
  lock = Lock_Cell(MEMORY_LOC (Base, Offset));
  if (Remember_Value != FAST_MEMORY_REF (Base, Offset))
  {
    Unlock_Cell(lock);
    goto Try_Again;
  }
  if (Old_Value == Desired)
  {
    Do_Store_No_Lock(MEMORY_LOC (Base, Offset), New);
    success = true;
  }
  else
  {
    success = false;
  }
  Unlock_Cell(lock);
  return success;
}

DEFINE_PRIMITIVE ("SET-CAR-IF-EQ?!", Prim_set_car_if_eq, 3, 3,
  "Replace the car of PAIR with NEW-VALUE iff it contains OLD-VALUE.\n\
Return PAIR if so, otherwise return '().")
{
  PRIMITIVE_HEADER (3);
  CHECK_ARG (1, PAIR_P);
  {
    fast SCHEME_OBJECT pair = (ARG_REF (1));
    if (Set_If_Equal (pair, CONS_CAR, (ARG_REF (2)), (ARG_REF (3))))
      PRIMITIVE_RETURN (pair);
  }
  PRIMITIVE_RETURN (EMPTY_LIST);
}

DEFINE_PRIMITIVE ("SET-CDR-IF-EQ?!", Prim_set_cdr_if_eq, 3, 3,
  "Replace the cdr of PAIR with NEW-VALUE iff it contains OLD-VALUE.\n\
Return PAIR if so, otherwise return '().")
{
  PRIMITIVE_HEADER (3);
  CHECK_ARG (1, PAIR_P);
  {
    fast SCHEME_OBJECT pair = (ARG_REF (1));
    if (Set_If_Equal (pair, CONS_CDR, (ARG_REF (2)), (ARG_REF (3))))
      PRIMITIVE_RETURN (pair);
  }
  PRIMITIVE_RETURN (EMPTY_LIST);
}

/* (VECTOR-SET-IF-EQ?! <Vector> <Offset> <New Value> <Old Value>)
   Replaces the <Offset>th element of <Vector> with <New Value> if it used
   to contain <Old Value>.  The value returned is either <Vector> (if
   the modification takes place) or '() if it does not.
*/
DEFINE_PRIMITIVE ("VECTOR-SET-IF-EQ?!", Prim_vector_set_if_eq, 4, 4,
  "Replace VECTOR's INDEX'th element with NEW-VALUE iff it contains OLD-VALUE.\n\
Return VECTOR if so, otherwise return '().")
{
  PRIMITIVE_HEADER (4);
  CHECK_ARG (1, VECTOR_P);
  {
    fast SCHEME_OBJECT vector = (ARG_REF (1));
    if (Set_If_Equal
	(vector,
	 ((arg_index_integer (2, (VECTOR_LENGTH (vector)))) + 1),
	 (ARG_REF (3)),
	 (ARG_REF (4))))
      PRIMITIVE_RETURN (vector);
  }
  PRIMITIVE_RETURN (EMPTY_LIST);
}

DEFINE_PRIMITIVE ("SET-CXR-IF-EQ?!", Prim_set_cxr_if_eq, 4, 4,
  "Replace HUNK3's INDEX'th element with NEW-VALUE iff it contains OLD-VALUE.\n\
Return HUNK3 if so, otherwise return '().")
{
  PRIMITIVE_HEADER (4);
  CHECK_ARG (1, HUNK3_P);
  {
    fast SCHEME_OBJECT hunk3 = (ARG_REF (1));
    if (Set_If_Equal
	(hunk3,
	 ((arg_index_integer (2, 3)) + 1),
	 (ARG_REF (3)),
	 (ARG_REF (4))))
      PRIMITIVE_RETURN (hunk3);
  }
  PRIMITIVE_RETURN (EMPTY_LIST);
}

DEFINE_PRIMITIVE ("FUTURE-SIZE", Prim_future_size, 1, 1,
  "Return the number of elements in FUTURE.\n\
This is similar to SYSTEM-VECTOR-SIZE,\n\
but works only on futures and doesn't touch them.")
{
  PRIMITIVE_HEADER (1)
  CHECK_ARG (1, FUTURE_P);
  PRIMITIVE_RETURN (LONG_TO_UNSIGNED_FIXNUM (VECTOR_LENGTH (ARG_REF (1))));
}

DEFINE_PRIMITIVE ("FUTURE-REF", Prim_future_ref, 2, 2,
  "Return FUTURE's INDEX'th element.\n\
This is similar to SYSTEM-VECTOR-REF,\n\
but works only on futures and doesn't touch them.")
{
  PRIMITIVE_HEADER (2);
  CHECK_ARG (1, FUTURE_P);
  {
    fast SCHEME_OBJECT future = (ARG_REF (1));
    PRIMITIVE_RETURN
      (VECTOR_REF
       (future, (arg_index_integer (2, (VECTOR_LENGTH (future))))));
  }
}

DEFINE_PRIMITIVE ("FUTURE-SET!", Prim_future_set, 3, 3,
  "Modify FUTURE's INDEX'th element to be VALUE.\n\
This is similar to SYSTEM-VECTOR-SET!,\n\
but works only on futures and doesn't touch them.")
{
  PRIMITIVE_HEADER (3);
  CHECK_ARG (1, FUTURE_P);
  {
    fast SCHEME_OBJECT future = (ARG_REF (1));
    fast long index = (arg_index_integer (2, (VECTOR_LENGTH (future))));
    fast SCHEME_OBJECT result = (VECTOR_REF (future, index));
    VECTOR_SET (future, index, (ARG_REF (3)));
    PRIMITIVE_RETURN (result);
  }
}

DEFINE_PRIMITIVE ("LOCK-FUTURE!", Prim_lock_future, 1, 1,
  "Set the lock flag on FUTURE.\n\
This flag prevents FUTURE from being spliced out by the garbage collector.\n\
If FUTURE is not a future, return #F immediately,\n\
otherwise return #T after the lock has been set.\n\
Will wait as long as necessary for the lock to be set.")
{
  PRIMITIVE_HEADER (1);
  {
    fast SCHEME_OBJECT future = (ARG_REF (1));
    if (! (FUTURE_P (future)))
      PRIMITIVE_RETURN (SHARP_F);
    while (1)
      {
	if (INTERRUPT_PENDING_P (INT_Mask))
	  signal_interrupt_from_primitive ();
	{
	  fast SCHEME_OBJECT lock;
	  SWAP_POINTERS ((MEMORY_LOC (future, FUTURE_LOCK)), SHARP_T, lock);
	  if (lock == SHARP_F)
	    PRIMITIVE_RETURN (SHARP_T);
	}
	Sleep (CONTENTION_DELAY);
      }
  }
}

DEFINE_PRIMITIVE ("UNLOCK-FUTURE!", Prim_unlock_future, 1, 1,
  "Clear the lock flag on FUTURE.\n\
If FUTURE is not a future, return #F immediately,\n\
otherwise return #T after the lock has been cleared.")
{
  PRIMITIVE_HEADER (1);
  {
    fast SCHEME_OBJECT future = (ARG_REF (1));
    if (! (FUTURE_P (future)))
      PRIMITIVE_RETURN (SHARP_F);
    if (! (Future_Is_Locked (future)))
      error_wrong_type_arg (1);
    MEMORY_SET (future, FUTURE_LOCK, SHARP_F);
    PRIMITIVE_RETURN (SHARP_T);
  }
}

DEFINE_PRIMITIVE ("FUTURE->VECTOR", Prim_future_to_vector, 1, 1,
  "Return a newly-allocated vector containing FUTURE's elements.
If FUTURE is not a future, return #F instead.")
{
  PRIMITIVE_HEADER (1);
  {
    SCHEME_OBJECT future = (ARG_REF (1));
    if (! (FUTURE_P (future)))
      PRIMITIVE_RETURN (SHARP_F);
    {
      long length = (VECTOR_LENGTH (future));
      fast SCHEME_OBJECT * scan_source = (MEMORY_LOC (future, 1));
      fast SCHEME_OBJECT * end_source = (scan_source + length);
      SCHEME_OBJECT result =
	(allocate_marked_vector (TC_VECTOR, length, true));
      fast SCHEME_OBJECT * scan_result = (MEMORY_LOC (result, 1));
      while (scan_source < end_source)
	(*scan_result++) = (MEMORY_FETCH (*scan_source++));
      PRIMITIVE_RETURN (result);
    }
  }
}

DEFINE_PRIMITIVE ("NON-TOUCHING-EQ?", Prim_future_eq, 2, 2, 0)
{
  PRIMITIVE_HEADER (2);
  PRIMITIVE_RETURN (BOOLEAN_TO_OBJECT ((ARG_REF (1)) == (ARG_REF (2))));
}

/* MAKE-INITIAL-PROCESS is called to create a small stacklet which
 * will just call the specified thunk and then end the computation
 */

DEFINE_PRIMITIVE ("MAKE-INITIAL-PROCESS", Prim_make_initial_process, 1, 1, 0)
{
  SCHEME_OBJECT Result;
  long Useful_Length;
  PRIMITIVE_HEADER (1);

  Result = MAKE_POINTER_OBJECT (TC_CONTROL_POINT, Free);
  Useful_Length = (3 * CONTINUATION_SIZE) + STACK_ENV_EXTRA_SLOTS + 1;

#ifdef USE_STACKLETS

  {
    long Allocated_Length, Waste_Length;

    Allocated_Length = (Useful_Length + STACKLET_SLACK + STACKLET_HEADER_SIZE);
    if (Allocated_Length < Default_Stacklet_Size)
    {
      Allocated_Length = Default_Stacklet_Size;
      Waste_Length = ((Allocated_Length + 1) -
		      (Useful_Length + STACKLET_HEADER_SIZE));
    }
    else
    {
      Waste_Length = (STACKLET_SLACK + 1);
    }
    Primitive_GC_If_Needed(Allocated_Length + 1);
    Free[STACKLET_LENGTH] =
      MAKE_POINTER_OBJECT (TC_MANIFEST_VECTOR, Allocated_Length);
    Free[STACKLET_REUSE_FLAG] = SHARP_T;
    Free[STACKLET_UNUSED_LENGTH] =
      MAKE_OBJECT (TC_MANIFEST_NM_VECTOR, Waste_Length);
    Free += (Allocated_Length + 1) - Useful_Length;
  }

#else /* not USE_STACKLETS */

  Free[STACKLET_LENGTH] =
    MAKE_OBJECT (TC_MANIFEST_VECTOR, Useful_Length + STACKLET_HEADER_SIZE - 1);
  Free[STACKLET_REUSE_FLAG] = SHARP_F;
  Free[STACKLET_UNUSED_LENGTH] = MAKE_OBJECT (TC_MANIFEST_NM_VECTOR, 0);
  Free += STACKLET_HEADER_SIZE;

#endif /* USE_STACKLETS */

  Free[CONTINUATION_EXPRESSION] = LONG_TO_FIXNUM(FETCH_INTERRUPT_MASK());
  Free[CONTINUATION_RETURN_CODE] =
    MAKE_OBJECT (TC_RETURN_CODE, RC_RESTORE_INT_MASK);
  Free += CONTINUATION_SIZE;
  Free[CONTINUATION_EXPRESSION] = SHARP_F;
  Free[CONTINUATION_RETURN_CODE] =
    MAKE_OBJECT (TC_RETURN_CODE, RC_INTERNAL_APPLY);
  Free += CONTINUATION_SIZE;
  *Free++ = STACK_FRAME_HEADER;
  *Free++ = (ARG_REF (1));
  Free[CONTINUATION_EXPRESSION] = (ARG_REF (1)); /* For testing & debugging */
  Free[CONTINUATION_RETURN_CODE] =
    MAKE_OBJECT (TC_RETURN_CODE, RC_END_OF_COMPUTATION);
  Free += CONTINUATION_SIZE;
  PRIMITIVE_RETURN (Result);
}

/*
  Absolutely the cheapest future we can make.  This includes
  the I/O stuff and whatnot.  Notice that the name is required.

  (make-cheap-future orig-code user-proc name)

*/

DEFINE_PRIMITIVE ("MAKE-CHEAP-FUTURE", Prim_make_cheap_future, 3, 3, 0)
{
  PRIMITIVE_HEADER (3);
  {
    fast SCHEME_OBJECT future = (allocate_marked_vector (TC_FUTURE, 10, true));
    FAST_MEMORY_SET (future, FUTURE_IS_DETERMINED, SHARP_F);
    FAST_MEMORY_SET (future, FUTURE_LOCK, SHARP_F);
    FAST_MEMORY_SET (future, FUTURE_QUEUE, (cons (EMPTY_LIST, EMPTY_LIST)));
    FAST_MEMORY_SET (future, FUTURE_PROCESS, (ARG_REF (1)));
    FAST_MEMORY_SET (future, FUTURE_STATUS, SHARP_T);
    FAST_MEMORY_SET (future, FUTURE_ORIG_CODE, (ARG_REF (2)));
    /* Put the I/O system stuff here. */
    FAST_MEMORY_SET
      (future,
       FUTURE_PRIVATE,
       (make_vector
	(1,
	 (hunk3_cons
	  (SHARP_F,
	   (ARG_REF (3)),
	   (cons ((LONG_TO_UNSIGNED_FIXNUM (0)),
		  (char_pointer_to_string ("")))))),
	 true)));
    FAST_MEMORY_SET (future, FUTURE_WAITING_ON, EMPTY_LIST);
    FAST_MEMORY_SET (future, FUTURE_METERING, (New_Future_Number ()));
    FAST_MEMORY_SET (future, FUTURE_USER, SHARP_F);
    PRIMITIVE_RETURN (future);
  }
}
