buffer.h

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2011-2013, University of Amsterdam
                              VU University Amsterdam
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    modification, are permitted provided that the following conditions
    are met:

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       notice, this list of conditions and the following disclaimer.

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       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
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*/

#ifndef BUFFER_H_INCLUDED
#define BUFFER_H_INCLUDED

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Triples are buffered in an  array.  This   is  used  by transactions for
committing, etc. The data is   allocated using PL_malloc_uncollectable()
to make sure that discarded  triples  are   not  really  removed  by GC,
notably before their changes can be broadcasted.

FIXME: Check that all triple buffers are   allocated either on the stack
or in memory that is scanned  by   BDWGC.  The ones for transactions are
stored on the C-stack.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

#define TFAST_SIZE 64

typedef struct triple_buffer
{ triple **base;
  triple **top;
  triple **max;
  triple  *fast[TFAST_SIZE];
} triple_buffer;


static inline void
init_triple_buffer(triple_buffer *b)
{ b->base = b->top = b->fast;
  b->max = b->top + TFAST_SIZE;
}


static inline int
is_empty_buffer(triple_buffer *b)
{ return b->top == b->base;
}


static inline int
buffer_triple(triple_buffer *b, triple *t)
{ if ( b->top < b->max )
  { *b->top++ = t;
  } else
  { if ( b->base == b->fast )
    { triple **tmp = PL_malloc_uncollectable(TFAST_SIZE*2*sizeof(triple*));

      if ( tmp )
      { memcpy(tmp, b->base, (char*)b->top - (char*)b->base);
	b->base = tmp;
	b->max = b->base + TFAST_SIZE*2;
	b->top = b->base + TFAST_SIZE;
	*b->top++ = t;
      } else
	return FALSE;
    } else
    { size_t size = (b->max - b->base);
      triple **tmp = PL_malloc_uncollectable(size*2*sizeof(triple*));

      assert(b->top == b->max);

      if ( tmp )
      { memcpy(tmp, b->base, (char*)b->top - (char*)b->base);
	PL_free(b->base);
	b->base = tmp;
	b->top  = b->base + size;
	b->max  = b->base + size*2;
	*b->top++ = t;
      } else
	return FALSE;
    }
  }

  return TRUE;
}


static inline void
free_triple_buffer(triple_buffer *b)
{ if ( b->base && b->base != b->fast )
    PL_free(b->base);
}

#endif /*BUFFER_H_INCLUDED*/