内存池的实现-腾讯笔试

#ifndef _MEM_POOL_H
#define _MEM_POOL_H

#include <vector>
#include <iostream>
#include "Lock.h"

using namespace std;
class CMemPool
{
public:

    //创建大小为blockSize的内存块，内存池数目为预分配的数目preAlloc
    CMemPool(std::size_t blockSize, int preAlloc = 0, int maxAlloc = 0);
    ~CMemPool();

    //获取一个内存块。如果内存池中没有足够的内存块，则会自动分配新的内存块
    //如果分配的内存块数目达到了最大值，则会返回一个异常
    void* Get();

    //释放当前内存块，将其插入内存池
    void Release(void* ptr);

    //返回内存块大小
    std::size_t BlockSize() const;

    //返回内存池中内存块数目
    int Allocated() const;

    //返回内存池中可用的内存块数目
    int Available() const;

private:
    CMemPool();
    CMemPool(const CMemPool&);
    CMemPool& operator = (const CMemPool&);

    enum
    {
        BLOCK_RESERVE = 32
    };

    typedef std::vector<char*> BlockVec;

    std::size_t m_blockSize;
    int         m_maxAlloc;
    int         m_allocated;
    BlockVec    m_blocks;
    CMutex      m_mutex;
};

inline std::size_t CMemPool::BlockSize() const
{
    return m_blockSize;
}


inline int CMemPool::Allocated() const
{
    return m_allocated;
}


inline int CMemPool::Available() const
{
    return (int) m_blocks.size();
}


#endif

#include "MemPool.h"

CMemPool::CMemPool(std::size_t blockSize, int preAlloc, int maxAlloc):
m_blockSize(blockSize),
m_maxAlloc(maxAlloc),
m_allocated(preAlloc)
{
    if ( preAlloc < 0 || maxAlloc == 0 || maxAlloc < preAlloc )
    {
        cout<<"CMemPool::CMemPool parameter error."<<endl;
    }

    int r = BLOCK_RESERVE;
    if (preAlloc > r)
        r = preAlloc;
    if (maxAlloc > 0 && maxAlloc < r)
        r = maxAlloc;
    m_blocks.reserve(r);
    for (int i = 0; i < preAlloc; ++i)
    {
        m_blocks.push_back(new char[m_blockSize]);
    }
}


CMemPool::~CMemPool()
{
    for (BlockVec::iterator it = m_blocks.begin(); it != m_blocks.end(); ++it)
    {
        delete [] *it;
    }
}


void* CMemPool::Get()
{
    CLock lock(m_mutex);

    if (m_blocks.empty())
    {
        if (m_maxAlloc == 0 || m_allocated < m_maxAlloc)
        {
            ++m_allocated;
            return new char[m_blockSize];
        }
        else
        {
            cout<<"CMemPool::get CMemPool exhausted."<<endl;
            return (void *)NULL;
        }
    }
    else
    {
        char* ptr = m_blocks.back();
        m_blocks.pop_back();
        return ptr;
    }
}


void CMemPool::Release(void* ptr)
{
    CLock lock(m_mutex);

    m_blocks.push_back(reinterpret_cast<char*>(ptr));
}