collector.cpp

// -*- c-basic-offset: 2 -*-
/*
 *  This file is part of the KDE libraries
 *  Copyright (C) 2003 Apple Computer, Inc.
 *
 *  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 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
 *
 */

#include "collector.h"

#include "value.h"
#include "internal.h"

#ifndef MAX
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#endif

namespace KJS {

// tunable parameters
const int MINIMUM_CELL_SIZE = 56;
const int BLOCK_SIZE = (8 * 4096);
const int SPARE_EMPTY_BLOCKS = 2;
const int MIN_ARRAY_SIZE = 14;
const int GROWTH_FACTOR = 2;
const int LOW_WATER_FACTOR = 4;
const int ALLOCATIONS_PER_COLLECTION = 1000;

// derived constants
const int CELL_ARRAY_LENGTH = (MINIMUM_CELL_SIZE / sizeof(double)) + (MINIMUM_CELL_SIZE % sizeof(double) != 0 ? sizeof(double) : 0);
const int CELL_SIZE = CELL_ARRAY_LENGTH * sizeof(double);
const int CELLS_PER_BLOCK = ((BLOCK_SIZE * 8 - sizeof(int) * 8 - sizeof(void *) * 8) / (CELL_SIZE * 8));



struct CollectorCell {
  double memory[CELL_ARRAY_LENGTH];
};


struct CollectorBlock {
  CollectorCell cells[CELLS_PER_BLOCK];
  int usedCells;
  CollectorCell *freeList;
};

struct CollectorHeap {
  CollectorBlock **blocks;
  int numBlocks;
  int usedBlocks;
  int firstBlockWithPossibleSpace;

  CollectorCell **oversizeCells;
  int numOversizeCells;
  int usedOversizeCells;

  int numLiveObjects;
  int numAllocationsSinceLastCollect;
};

static CollectorHeap heap = {NULL, 0, 0, 0, NULL, 0, 0, 0, 0};

bool Collector::memoryFull = false;

void* Collector::allocate(size_t s)
{
  if (s == 0)
    return 0L;

  // collect if needed
  if (++heap.numAllocationsSinceLastCollect >= ALLOCATIONS_PER_COLLECTION) {
    collect();
  }

  if (s > (unsigned)CELL_SIZE) {
    // oversize allocator
    if (heap.usedOversizeCells == heap.numOversizeCells) {
      heap.numOversizeCells = MAX(MIN_ARRAY_SIZE, heap.numOversizeCells * GROWTH_FACTOR);
      heap.oversizeCells = (CollectorCell **)realloc(heap.oversizeCells, heap.numOversizeCells * sizeof(CollectorCell *));
    }

    void *newCell = malloc(s);
    heap.oversizeCells[heap.usedOversizeCells] = (CollectorCell *)newCell;
    heap.usedOversizeCells++;
    heap.numLiveObjects++;

    ((ValueImp *)(newCell))->_flags = 0;
    return newCell;
  }

  // slab allocator

  CollectorBlock *targetBlock = NULL;

  int i;
  for (i = heap.firstBlockWithPossibleSpace; i < heap.usedBlocks; i++) {
    if (heap.blocks[i]->usedCells < CELLS_PER_BLOCK) {
      targetBlock = heap.blocks[i];
      break;
    }
  }

  heap.firstBlockWithPossibleSpace = i;

  if (targetBlock == NULL) {
    // didn't find one, need to allocate a new block

    if (heap.usedBlocks == heap.numBlocks) {
      heap.numBlocks = MAX(MIN_ARRAY_SIZE, heap.numBlocks * GROWTH_FACTOR);
      heap.blocks = (CollectorBlock **)realloc(heap.blocks, heap.numBlocks * sizeof(CollectorBlock *));
    }

    targetBlock = (CollectorBlock *)calloc(1, sizeof(CollectorBlock));
    targetBlock->freeList = targetBlock->cells;
    heap.blocks[heap.usedBlocks] = targetBlock;
    heap.usedBlocks++;
  }

  // find a free spot in the block and detach it from the free list
  CollectorCell *newCell = targetBlock->freeList;

  ValueImp *imp = (ValueImp*)newCell;
  if (imp->_vd != NULL) {
    targetBlock->freeList = (CollectorCell*)(imp->_vd);
  } else if (targetBlock->usedCells == (CELLS_PER_BLOCK - 1)) {
    // last cell in this block
    targetBlock->freeList = NULL;
  } else {
    // all next pointers are initially 0, meaning "next cell"
    targetBlock->freeList = newCell + 1;
  }

  targetBlock->usedCells++;
  heap.numLiveObjects++;

  ((ValueImp *)(newCell))->_flags = 0;
  return (void *)(newCell);
}

bool Collector::collect()
{
  bool deleted = false;

  // MARK: first mark all referenced objects recursively
  // starting out from the set of root objects
  if (InterpreterImp::s_hook) {
    InterpreterImp *scr = InterpreterImp::s_hook;
    do {
      //fprintf( stderr, "Collector marking interpreter %p\n",(void*)scr);
      scr->mark();
      scr = scr->next;
    } while (scr != InterpreterImp::s_hook);
  }

  // mark any other objects that we wouldn't delete anyway
  for (int block = 0; block < heap.usedBlocks; block++) {

    int minimumCellsToProcess = heap.blocks[block]->usedCells;
    CollectorBlock *curBlock = heap.blocks[block];

    for (int cell = 0; cell < CELLS_PER_BLOCK; cell++) {
      if (minimumCellsToProcess < cell) {
    goto skip_block_mark;
      }

      ValueImp *imp = (ValueImp *)(curBlock->cells + cell);

      if (!(imp->_flags & ValueImp::VI_DESTRUCTED)) {

    if ((imp->_flags & (ValueImp::VI_CREATED|ValueImp::VI_MARKED)) == ValueImp::VI_CREATED &&
        ((imp->_flags & ValueImp::VI_GCALLOWED) == 0 || imp->refcount != 0)) {
      imp->mark();
    }
      } else {
    minimumCellsToProcess++;
      }
    }
  skip_block_mark: ;
  }

  for (int cell = 0; cell < heap.usedOversizeCells; cell++) {
    ValueImp *imp = (ValueImp *)heap.oversizeCells[cell];
    if ((imp->_flags & (ValueImp::VI_CREATED|ValueImp::VI_MARKED)) == ValueImp::VI_CREATED &&
    ((imp->_flags & ValueImp::VI_GCALLOWED) == 0 || imp->refcount != 0)) {
      imp->mark();
    }
  }

  // SWEEP: delete everything with a zero refcount (garbage) and unmark everything else

  int emptyBlocks = 0;

  for (int block = 0; block < heap.usedBlocks; block++) {
    CollectorBlock *curBlock = heap.blocks[block];

    int minimumCellsToProcess = curBlock->usedCells;

    for (int cell = 0; cell < CELLS_PER_BLOCK; cell++) {
      if (minimumCellsToProcess < cell) {
    goto skip_block_sweep;
      }

      ValueImp *imp = (ValueImp *)(curBlock->cells + cell);

      if (!(imp->_flags & ValueImp::VI_DESTRUCTED)) {
    if (!imp->refcount && imp->_flags == (ValueImp::VI_GCALLOWED | ValueImp::VI_CREATED)) {
      //fprintf( stderr, "Collector::deleting ValueImp %p (%s)\n", (void*)imp, typeid(*imp).name());
      // emulate destructing part of 'operator delete()'
      imp->~ValueImp();
      curBlock->usedCells--;
      heap.numLiveObjects--;
      deleted = true;

      // put it on the free list
      imp->_vd = (ValueImpPrivate*)curBlock->freeList;
      curBlock->freeList = (CollectorCell *)imp;

    } else {
      imp->_flags &= ~ValueImp::VI_MARKED;
    }
      } else {
    minimumCellsToProcess++;
      }
    }

  skip_block_sweep:

    if (heap.blocks[block]->usedCells == 0) {
      emptyBlocks++;
      if (emptyBlocks > SPARE_EMPTY_BLOCKS) {
#ifndef DEBUG_COLLECTOR
    free(heap.blocks[block]);
#endif
    // swap with the last block so we compact as we go
    heap.blocks[block] = heap.blocks[heap.usedBlocks - 1];
    heap.usedBlocks--;
    block--; // Don't move forward a step in this case

    if (heap.numBlocks > MIN_ARRAY_SIZE && heap.usedBlocks < heap.numBlocks / LOW_WATER_FACTOR) {
      heap.numBlocks = heap.numBlocks / GROWTH_FACTOR;
      heap.blocks = (CollectorBlock **)realloc(heap.blocks, heap.numBlocks * sizeof(CollectorBlock *));
    }
      }
    }
  }

  if (deleted) {
    heap.firstBlockWithPossibleSpace = 0;
  }

  int cell = 0;
  while (cell < heap.usedOversizeCells) {
    ValueImp *imp = (ValueImp *)heap.oversizeCells[cell];

    if (!imp->refcount &&
    imp->_flags == (ValueImp::VI_GCALLOWED | ValueImp::VI_CREATED)) {

      imp->~ValueImp();
#ifndef DEBUG_COLLECTOR
      free((void *)imp);
#endif

      // swap with the last oversize cell so we compact as we go
      heap.oversizeCells[cell] = heap.oversizeCells[heap.usedOversizeCells - 1];

      heap.usedOversizeCells--;
      deleted = true;
      heap.numLiveObjects--;

      if (heap.numOversizeCells > MIN_ARRAY_SIZE && heap.usedOversizeCells < heap.numOversizeCells / LOW_WATER_FACTOR) {
    heap.numOversizeCells = heap.numOversizeCells / GROWTH_FACTOR;
    heap.oversizeCells = (CollectorCell **)realloc(heap.oversizeCells, heap.numOversizeCells * sizeof(CollectorCell *));
      }

    } else {
      imp->_flags &= ~ValueImp::VI_MARKED;
      cell++;
    }
  }

  heap.numAllocationsSinceLastCollect = 0;

  memoryFull = (heap.numLiveObjects >= KJS_MEM_LIMIT);

  return deleted;
}

int Collector::size()
{
  return heap.numLiveObjects;
}

#ifdef KJS_DEBUG_MEM
void Collector::finalCheck()
{
}
#endif

} // namespace KJS