mariadb-columnstore-engine/utils/common/poolallocator.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. */

/******************************************************************************************
* $Id$
*
******************************************************************************************/

/* This allocator is an attempt to consolidate small allocations and
   deallocations to boost performance and reduce mem fragmentation. */

#ifndef POOLALLOCATOR_H_
#define POOLALLOCATOR_H_

#include <unistd.h>
#include <stdint.h>
#include <vector>
#include <map>
#include <boost/shared_array.hpp>
#include <atomic>

namespace utils
{

class PoolAllocator
{
public:
    static const unsigned DEFAULT_WINDOW_SIZE = 4096 * 40;  // should be an integral # of pages

    explicit PoolAllocator(unsigned windowSize = DEFAULT_WINDOW_SIZE, bool isTmpSpace = false, bool _useLock = false) :
        allocSize(windowSize),
        tmpSpace(isTmpSpace),
        capacityRemaining(0),
        memUsage(0),
        nextAlloc(0),
        useLock(_useLock),
        lock(false) { }
    PoolAllocator(const PoolAllocator& p) :
        allocSize(p.allocSize),
        tmpSpace(p.tmpSpace),
        capacityRemaining(0),
        memUsage(0),
        nextAlloc(0),
        useLock(p.useLock),
        lock(false) { }
    virtual ~PoolAllocator() {}

    PoolAllocator& operator=(const PoolAllocator&);

    void* allocate(uint64_t size);
    void deallocate(void* p);
    void deallocateAll();

    inline uint64_t getMemUsage() const
    {
        return memUsage;
    }
    unsigned getWindowSize() const
    {
        return allocSize;
    }

    void setUseLock(bool ul)
    {
        useLock = ul;
    }

private:
    void newBlock();
    void *allocOOB(uint64_t size);

    unsigned allocSize;
    std::vector<boost::shared_array<uint8_t> > mem;
    bool tmpSpace;
    unsigned capacityRemaining;
    uint64_t memUsage;
    uint8_t* nextAlloc;
    bool useLock;
    std::atomic<bool> lock;

    struct OOBMemInfo
    {
        boost::shared_array<uint8_t> mem;
        uint64_t size;
    };
    typedef std::map<void*, OOBMemInfo> OutOfBandMap;
    OutOfBandMap oob;  // for mem chunks bigger than the window size; these can be dealloc'd
};

inline void* PoolAllocator::allocate(uint64_t size)
{
    void *ret;
    bool _false = false;

    if (useLock)
        while (!lock.compare_exchange_weak(_false, true, std::memory_order_acquire))
            _false = false;

    if (size > allocSize)
    {
        ret = allocOOB(size);
        if (useLock)
            lock.store(false, std::memory_order_release);
        return ret;
    }

    if (size > capacityRemaining)
        newBlock();

    ret = (void*) nextAlloc;
    nextAlloc += size;
    capacityRemaining -= size;
    memUsage += size;
    if (useLock)
        lock.store(false, std::memory_order_release);
    return ret;
}

}

#endif