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tdelibs/kjs/collector.cpp

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/*
* 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"
#include <limits.h>
#include <typeinfo>
#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) {
static const size_t maxNumBlocks = ULONG_MAX / sizeof(CollectorBlock*) / GROWTH_FACTOR;
if ((size_t)heap.numBlocks > maxNumBlocks)
return 0L;
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, "[kjs-collector] 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, "[kjs-collector] Collector::deleting ValueImp %p (%s)\n", (void*)imp, typeid(*imp).name());
// prevent double free
imp->_flags |= ValueImp::VI_DESTRUCTED;
// 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