CGenericMemoryPool.h

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/* +---------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)               |
   |                          http://www.mrpt.org/                             |
   |                                                                           |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file        |
   | See: http://www.mrpt.org/Authors - All rights reserved.                   |
   | Released under BSD License. See details in http://www.mrpt.org/License    |
   +---------------------------------------------------------------------------+ */
#ifndef  MRPT_MEMORY_POOL_H
#define  MRPT_MEMORY_POOL_H

#include <mrpt/synch/CCriticalSection.h>
#include <list>

namespace mrpt
{
        namespace system
        {
                /** A generic system for versatile memory pooling.
                  *   This class implements the singleton pattern so a unique instance exists for each combination of template parameters.
                  *   All methods are thread-safe.
                  *
                  *   Basic usage:
                  *     - When needed, call \a request_memory() to check the availability of memory in the pool.
                  *             - At your class destructor, donate the memory to the pool with \a dump_to_pool().
                  *
                  *   Notice that memory requests are checked against memory blocks in the pool via a user-defined function:
                  *
                  *    bool POOLABLE_DATA::isSuitable(const POOLABLE_DATA & req) const { ... }
                  *
                  *   For an example of how to handle a memory pool, see the class mrpt::obs::CObservation3DRangeScan
                  *
                  *  \tparam POOLABLE_DATA A struct with user-defined objects which actually contain the memory blocks (e.g. one or more std::vector).
                  *  \tparam DATA_PARAMS A struct with user information about each memory block (e.g. size of a std::vector)
                  * \ingroup mrpt_memory
                  */
                template <class DATA_PARAMS,class POOLABLE_DATA>
                class CGenericMemoryPool
                {
                private:
                        typedef std::list<std::pair<DATA_PARAMS,POOLABLE_DATA*> > TList;
                        TList                          m_pool;
                        mrpt::synch::CCriticalSection  m_pool_cs;
                        size_t                         m_maxPoolEntries;
                        bool                           & m_was_destroyed;  //!< With this trick we get rid of the "global destruction order fiasco" ;-)

                        CGenericMemoryPool(const size_t max_pool_entries, bool &was_destroyed ) : m_maxPoolEntries(max_pool_entries), m_was_destroyed(was_destroyed)
                        {
                                m_was_destroyed = false;
                        }

                public:
                        inline size_t getMemoryPoolMaxSize() const                     { return m_maxPoolEntries; }
                        inline void   setMemoryPoolMaxSize(const size_t maxNumEntries) { m_maxPoolEntries = maxNumEntries; }

                        /** Construct-on-first-use (~singleton) pattern: Return the unique instance of this class for a given template arguments,
                          *  or NULL if it was once created but it's been destroyed (which means we're in the program global destruction phase).
                          */
                        static CGenericMemoryPool<DATA_PARAMS,POOLABLE_DATA> * getInstance(const size_t max_pool_entries = 5)
                        {
                                static bool was_destroyed = false;
                                static CGenericMemoryPool<DATA_PARAMS,POOLABLE_DATA> inst(max_pool_entries, was_destroyed);
                                return was_destroyed ? NULL : &inst;
                        }

                        /** Request a block of data which fulfils the size requirements stated in \a params.
                          *  Notice that the decision on the suitability of each pool'ed block is done by DATA_PARAMS::isSuitable().
                          *  \return The block of data, or NULL if none suitable was found in the pool.
                          *  \note It is a responsibility of the user to free with "delete" the "POOLABLE_DATA" object itself once the memory has been extracted from its elements.
                          */
                        POOLABLE_DATA * request_memory(const DATA_PARAMS &params)
                        {
                                // A quick check first:
                                if (m_pool.empty()) return NULL;

                                mrpt::synch::CCriticalSectionLocker lock( &m_pool_cs );
                                for (typename TList::iterator it=m_pool.begin();it!=m_pool.end();++it) {
                                        if (it->first.isSuitable(params))
                                        {
                                                POOLABLE_DATA * ret = it->second;
                                                m_pool.erase(it);
                                                return ret;
                                        }
                                }
                                return NULL;
                        }

                        /** Saves the passed data block (characterized by \a params) to the pool.
                          *  If the overall size of the pool is above the limit, the oldest entry is removed.
                          *  \note It is a responsibility of the user to allocate in dynamic memory the "POOLABLE_DATA" object with "new".
                          */
                        void dump_to_pool(const DATA_PARAMS &params, POOLABLE_DATA *block)
                        {
                                mrpt::synch::CCriticalSectionLocker lock( &m_pool_cs );

                                while (m_pool.size()>=m_maxPoolEntries) // Free old data if needed
                                {
                                        if (m_pool.begin()->second) delete m_pool.begin()->second;
                                        m_pool.erase(m_pool.begin());
                                }

                                m_pool.push_back( typename TList::value_type(params,block) );
                        }

                        ~CGenericMemoryPool()
                        {
                                m_was_destroyed = true;
                                // Free remaining memory blocks:
                                mrpt::synch::CCriticalSectionLocker lock( &m_pool_cs );
                                for (typename TList::iterator it=m_pool.begin();it!=m_pool.end();++it)
                                        delete it->second;
                                m_pool.clear();
                        }
                };

        } // End of namespace
} // End of namespace

#endif