mariadb-columnstore-engine/utils/common/simpleallocator.h

/* Copyright (C) 2014 InfiniDB, Inc.

   This program 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; version 2 of
   the License.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

/******************************************************************************
 * $Id: simpleallocator.h 3495 2013-01-21 14:09:51Z rdempsey $
 *
 ******************************************************************************/

/** @file
 * class SimpleAllocator interface
 */

#pragma once

#include <unistd.h>
#include <list>
#include <stdint.h>
#include <limits>
#include <memory>

#undef min
#undef max

namespace utils
{
// A specialized allocator for std::tr1::unordered_multimap<uint64_t, uint64_t> based joiner
// or std::tr1::unordered_map<uint8_t*, uint8_t*> based aggregation.
// User shall initialize a pool and pass it to allocator, release the pool when map is done.
template <typename T>
class SimpleAllocator;

// this pool is best for node size of 3*sizeof(int64).
// map nodes are taken from fixed size blocks, and control hash tables are from ::new.
// assumption is the nodes are not reallocated, but the controls will reallocated when rehash.
// efficient only if the map does not remove nodes, otherwise will take more memory.

#define OPT_NODE_UNITS 10
class SimplePool
{
 public:
  SimplePool() : fNext(NULL), fEnd(NULL), fTableMemSize(0)
  {
  }
  ~SimplePool()
  {
    reset();
  }

  inline void* allocate(size_t n, const void* = 0);
  inline void deallocate(void* p, size_t n);
  inline size_t max_size() const throw();
  inline uint64_t getMemUsage() const;

 private:
  static const size_t fUnitPerChunk = OPT_NODE_UNITS * 10240;

  inline void reset();
  inline void allocateNewChunk();

  // MemUnit stores a pointer to next unit before allocated, and T after allocated.
  union MemUnit
  {
    MemUnit* fNext;
    uint64_t fData;
  } * fNext, *fEnd;  // fNext: next available unit, fEnd: one off the last unit

  std::list<MemUnit*> fBlockList;
  uint64_t fTableMemSize;

  static const size_t fUnitSize = sizeof(MemUnit);
  static const size_t fMaxNodeSize = fUnitSize * OPT_NODE_UNITS;
  static const size_t fChunkSize = fUnitSize * fUnitPerChunk;
};

template <typename T>
class SimpleAllocator
{
 public:
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
  typedef T* pointer;
  typedef const T* const_pointer;
  typedef T& reference;
  typedef const T& const_reference;
  typedef T value_type;
  template <typename U>
  struct rebind
  {
    typedef SimpleAllocator<U> other;
  };

  SimpleAllocator() throw()
  {
  }
  SimpleAllocator(std::shared_ptr<SimplePool> pool) throw()
  {
    fPool = pool;
  }
  SimpleAllocator(const SimpleAllocator& alloc)
  {
    fPool = alloc.fPool;
  }
  template <class U>
  SimpleAllocator(const SimpleAllocator<U>& alloc)
  {
    fPool = alloc.fPool;
  }

  ~SimpleAllocator() throw()
  {
  }

  inline pointer address(reference x) const
  {
    return &x;
  }
  inline const_pointer address(const_reference x) const
  {
    return &x;
  }

  inline pointer allocate(size_type n, const void* = 0)
  {
    return static_cast<pointer>(fPool->allocate(n * sizeof(T)));
  }
  inline void deallocate(pointer p, size_type n)
  {
    fPool->deallocate(p, n * sizeof(T));
  }

  inline size_type max_size() const throw()
  {
    return fPool->max_size() / sizeof(T);
  }
  inline void construct(pointer ptr, const T& val)
  {
    new ((void*)ptr) T(val);
  }
  inline void destroy(pointer ptr)
  {
    ptr->T::~T();
  }

  inline void setPool(SimplePool* pool)
  {
    fPool.reset(pool);
  }

  std::shared_ptr<SimplePool> fPool;
};

// inlines
inline void* SimplePool::allocate(size_t n, const void* dur)
{
  // make sure the block allocated is on unit boundary
  size_t unitCount = n / fUnitSize;

  if ((n % fUnitSize) != 0)
    unitCount += 1;

  // if for control table, let new allocator handle it.
  if (unitCount > OPT_NODE_UNITS)
  {
    fTableMemSize += n;
    return new uint8_t[n];
  }

  // allocate node
  MemUnit* curr = fNext;

  do
  {
    if (curr == NULL)
    {
      allocateNewChunk();
      curr = fNext;
    }

    fNext = curr + unitCount;

    if (fNext > fEnd)
      curr = NULL;
  } while (!curr);

  return curr;
}

inline void SimplePool::deallocate(void* p, size_t n)
{
  // only delete the old control table, which is allocated by new allocator.
  if (n > fMaxNodeSize)
  {
    fTableMemSize -= n;
    delete[](static_cast<uint8_t*>(p));
  }
}

inline size_t SimplePool::max_size() const throw()
{
  return fUnitSize * fUnitPerChunk;
}

inline uint64_t SimplePool::getMemUsage() const
{
  return fTableMemSize + fBlockList.size() * fChunkSize +
         // add list overhead, element type is a pointer, and
         // lists store a next pointer.
         fBlockList.size() * 2 * sizeof(void*);
}

inline void SimplePool::reset()
{
  for (std::list<MemUnit*>::iterator i = fBlockList.begin(); i != fBlockList.end(); i++)
    delete[](*i);

  fNext = NULL;
  fEnd = NULL;
}

inline void SimplePool::allocateNewChunk()
{
  MemUnit* chunk = new MemUnit[fUnitPerChunk];
  fBlockList.push_back(chunk);
  fNext = chunk;
  fEnd = chunk + fUnitPerChunk;
}

template <typename T1, typename T2>
inline bool operator==(const SimpleAllocator<T1>&, const SimpleAllocator<T2>&)
{
  return true;
}

template <typename T1, typename T2>
inline bool operator!=(const SimpleAllocator<T1>&, const SimpleAllocator<T2>&)
{
  return false;
}
}  // namespace utils