kdelibs/kdecore/util/kallocator.cpp

/*
    This file is part of the KDE libraries

    Copyright (C) 1999 Waldo Bastian (bastian@kde.org)
    Copyright (C) 2002 Michael Matz (matz@kde.org)

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library 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
    Library General Public License for more details.

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

/* Fast zone memory allocator with deallocation support, for use as obstack
   or as general purpose allocator.  It does no compaction.  If the usage
   pattern is non-optimal it might waste some memory while running.  E.g.
   allocating many small things at once, and then deallocating only every
   second one, there is a high chance, that actually no memory is freed.
 */

#include "kallocator.h"

#include <QList>

#include <stdio.h>

class KZoneAllocator::MemBlock
{
  public:
    MemBlock(size_t s) : size(s), ref(0), older(0), newer(0)
      { begin = new char[s]; }
    ~MemBlock() { delete [] begin; }
    bool is_in(void *ptr) const {return !(begin > (char *)ptr
    				          || (begin + size) <= (char *)ptr); }
    size_t size;
    unsigned int ref;
    char *begin;
    MemBlock *older;
    MemBlock *newer;
};

class KZoneAllocator::Private
{
public:
    Private()
        : currentBlock(0), blockSize(1),
          blockOffset(0), log2(0), num_blocks(0),
          hashList(0), hashSize(0), hashDirty(true)
    {
    }

    /** One block is 'current' to satisfy requests. @internal */
    MemBlock *currentBlock; 
    /** Store block size from constructor. @internal */
    unsigned long blockSize; 
    /** Store offset into current block; size-offset is free. @internal */
    unsigned long blockOffset;
    /** base-2 log of the block size. @internal */
    unsigned int log2;
    /** Count total number of allocated blocks. @internal */
    unsigned int num_blocks;
    /** Collection of lists of blocks, for lookups. @internal */
    MemList **hashList;
    /** Count of hashes. @internal */
    unsigned int hashSize;
    /** Flag the hashes as in need of reorganization. @internal */
    bool hashDirty;
};

KZoneAllocator::KZoneAllocator(unsigned long _blockSize)
    : d( new Private )
{
    while (d->blockSize < _blockSize) {
        d->blockSize <<= 1;
        d->log2++;
    }

    /* Make sure, that a block is allocated at the first time allocate()
       is called (even with a 0 size).  */
    d->blockOffset = d->blockSize + 1;
}

KZoneAllocator::~KZoneAllocator()
{
  unsigned int count = 0;
  if (d->hashList) {
    /* No need to maintain the different lists in d->hashList[] anymore.
       I.e. no need to use delBlock().  */
    for (unsigned int i = 0; i < d->hashSize; i++)
      delete d->hashList[i];
    delete [] d->hashList;
    d->hashList = 0;
  }
  MemBlock *next;
  for (; d->currentBlock; d->currentBlock = next) {
    next = d->currentBlock->older;
    delete d->currentBlock;
    count++;
  }
#ifndef NDEBUG // as this is called quite late in the app, we don't care
	       // to use qDebug
  if (count > 1)
    fprintf(stderr, "zone still contained %d blocks", count);
#endif
  delete d;
}

void KZoneAllocator::insertHash(MemBlock *b)
{
  quintptr adr = ((quintptr)b->begin) & (~(d->blockSize - 1));
  quintptr end = ((quintptr)b->begin) + d->blockSize;
  while (adr < end) {
    quintptr key = adr >> d->log2;
    key = key & (d->hashSize - 1);
    if (!d->hashList[key])
      d->hashList[key] = new QList<MemBlock *>;
    d->hashList[key]->append(b);
    adr += d->blockSize;
  }
}

/** Add a new memory block to the pool of blocks,
    and reorganize the hash lists if needed.
    @param b block to add
    @internal
*/
void KZoneAllocator::addBlock(MemBlock *b)
{
  b->newer = 0;
  b->older = d->currentBlock;
  if (d->currentBlock)
    b->older->newer = b;
  d->currentBlock = b;
  d->num_blocks++;
  /* If we either have no d->hashList at all, or since it's last construction
     there are now many more blocks we reconstruct the list.  But don't
     make it larger than a certain maximum.  */
  if (d->hashList && ((d->num_blocks / 4) > d->hashSize && d->hashSize < 64*1024))
    d->hashDirty = true;
  /* Only insert this block into the hashlists, if we aren't going to
     reconstruct them anyway.  */
  if (d->hashList && !d->hashDirty)
    insertHash (b);
}

/** Reinitialize hash list. @internal */
void KZoneAllocator::initHash()
{
  if (d->hashList) {
    for (unsigned int i = 0; i < d->hashSize; i++)
      delete d->hashList[i];
    delete [] d->hashList;
    d->hashList = 0;
  }
  d->hashSize = 1;
  while (d->hashSize < d->num_blocks)
    d->hashSize <<= 1;
  if (d->hashSize < 1024)
    d->hashSize = 1024;
  if (d->hashSize > 64*1024)
    d->hashSize = 64*1024;
  d->hashList = new QList<MemBlock *> *[d->hashSize];
  memset (d->hashList, 0, sizeof(QList<MemBlock*> *) * d->hashSize);
  d->hashDirty = false;
  for (MemBlock *b = d->currentBlock; b; b = b->older)
    insertHash(b);
}

/** Delete a memory block. This @em really returns the memory to the heap.
    @param b block to delete
    @internal
*/
void KZoneAllocator::delBlock(MemBlock *b)
{
  /* Update also the hashlists if we aren't going to reconstruct them
     soon.  */
  if (d->hashList && !d->hashDirty) {
    quintptr adr = (( quintptr )b->begin) & (~(d->blockSize - 1));
    quintptr end = (( quintptr )b->begin) + d->blockSize;
    while (adr < end) {
      quintptr key = adr >> d->log2;
      key = key & (d->hashSize - 1);
      if (d->hashList[key]) {
	QList<MemBlock *> *list = d->hashList[key];
	QList<MemBlock *>::Iterator it = list->begin();
	QList<MemBlock *>::Iterator endit = list->end();
	for (; it != endit; ++it)
	  if (*it == b) {
	    list->erase(it);
	    break;
	  }
      }
      adr += d->blockSize;
    }
  }
  if (b->older)
    b->older->newer = b->newer;
  if (b->newer)
    b->newer->older = b->older;
  if (b == d->currentBlock) {
    d->currentBlock = 0;
    d->blockOffset = d->blockSize;
  }
  delete b;
  d->num_blocks--;
}

void *
KZoneAllocator::allocate(size_t _size)
{
   // Use the size of (void *) as alignment
   const size_t alignment = sizeof(void *) - 1;
   _size = (_size + alignment) & ~alignment;   

   if ((unsigned long) _size + d->blockOffset > d->blockSize)
   {
      if (_size > d->blockSize) {
	qDebug("KZoneAllocator: allocating more than %lu bytes", d->blockSize);
	return 0;
      }
      addBlock(new MemBlock(d->blockSize));
      d->blockOffset = 0;
      //qDebug ("Allocating block #%d (%x)\n", d->num_blocks, d->currentBlock->begin);
   }
   void *result = (void *)(d->currentBlock->begin+d->blockOffset);
   d->currentBlock->ref++;
   d->blockOffset += _size;
   return result;
}

void
KZoneAllocator::deallocate(void *ptr)
{
  if (d->hashDirty)
    initHash();

  quintptr key = (((quintptr)ptr) >> d->log2) & (d->hashSize - 1);
  const QList<MemBlock *> *list = d->hashList[key];
  if (!list) {
    /* Can happen with certain usage pattern of intermixed free_since()
       and deallocate().  */
    //qDebug("Uhoh");
    return;
  }
  QList<MemBlock*>::ConstIterator it = list->begin();
  QList<MemBlock*>::ConstIterator endit = list->end();
  for (; it != endit; ++it) {
    MemBlock *cur = *it;
    if (cur->is_in(ptr)) {
      if (!--cur->ref) {
	if (cur != d->currentBlock)
	  delBlock (cur);
	else
	  d->blockOffset = 0;
      }
      return;
    }
  }
  /* Can happen with certain usage pattern of intermixed free_since()
     and deallocate().  */
  //qDebug("Uhoh2");
}

void
KZoneAllocator::free_since(void *ptr)
{
  /* If we have a d->hashList and it's not yet dirty, see, if we will dirty
     it by removing too many blocks.  This will make the below delBlock()s
     faster.  */
  if (d->hashList && !d->hashDirty)
    {
      const MemBlock *b;
      unsigned int removed = 0;
      for (b = d->currentBlock; b; b = b->older, removed++)
	if (b->is_in (ptr))
	  break;
      if (d->hashSize >= 4 * (d->num_blocks - removed))
        d->hashDirty = true;
    }
  while (d->currentBlock && !d->currentBlock->is_in(ptr)) {
    d->currentBlock = d->currentBlock->older;
    delBlock (d->currentBlock->newer);
  }
  d->blockOffset = ((char*)ptr) - d->currentBlock->begin;
}