rippled/modules/ripple_basics/json/json_batchallocator.h

//------------------------------------------------------------------------------
/*
    Copyright (c) 2011-2013, OpenCoin, Inc.
*/
//==============================================================================

#ifndef JSONCPP_BATCHALLOCATOR_H_INCLUDED
#define JSONCPP_BATCHALLOCATOR_H_INCLUDED

#ifndef JSONCPP_DOC_EXCLUDE_IMPLEMENTATION

namespace Json
{

/* Fast memory allocator.
 *
 * This memory allocator allocates memory for a batch of object (specified by
 * the page size, the number of object in each page).
 *
 * It does not allow the destruction of a single object. All the allocated objects
 * can be destroyed at once. The memory can be either released or reused for future
 * allocation.
 *
 * The in-place new operator must be used to construct the object using the pointer
 * returned by allocate.
 */
template < typename AllocatedType
, const unsigned int objectPerAllocation >
class BatchAllocator
{
public:
    typedef AllocatedType Type;

    BatchAllocator ( unsigned int objectsPerPage = 255 )
        : freeHead_ ( 0 )
        , objectsPerPage_ ( objectsPerPage )
    {
        //      printf( "Size: %d => %s\n", sizeof(AllocatedType), typeid(AllocatedType).name() );
        assert ( sizeof (AllocatedType) * objectPerAllocation >= sizeof (AllocatedType*) ); // We must be able to store a slist in the object free space.
        assert ( objectsPerPage >= 16 );
        batches_ = allocateBatch ( 0 );  // allocated a dummy page
        currentBatch_ = batches_;
    }

    ~BatchAllocator ()
    {
        for ( BatchInfo* batch = batches_; batch;  )
        {
            BatchInfo* nextBatch = batch->next_;
            free ( batch );
            batch = nextBatch;
        }
    }

    /// allocate space for an array of objectPerAllocation object.
    /// @warning it is the responsability of the caller to call objects constructors.
    AllocatedType* allocate ()
    {
        if ( freeHead_ ) // returns node from free list.
        {
            AllocatedType* object = freeHead_;
            freeHead_ = * (AllocatedType**)object;
            return object;
        }

        if ( currentBatch_->used_ == currentBatch_->end_ )
        {
            currentBatch_ = currentBatch_->next_;

            while ( currentBatch_  &&  currentBatch_->used_ == currentBatch_->end_ )
                currentBatch_ = currentBatch_->next_;

            if ( !currentBatch_  ) // no free batch found, allocate a new one
            {
                currentBatch_ = allocateBatch ( objectsPerPage_ );
                currentBatch_->next_ = batches_; // insert at the head of the list
                batches_ = currentBatch_;
            }
        }

        AllocatedType* allocated = currentBatch_->used_;
        currentBatch_->used_ += objectPerAllocation;
        return allocated;
    }

    /// Release the object.
    /// @warning it is the responsability of the caller to actually destruct the object.
    void release ( AllocatedType* object )
    {
        assert ( object != 0 );
        * (AllocatedType**)object = freeHead_;
        freeHead_ = object;
    }

private:
    struct BatchInfo
    {
        BatchInfo* next_;
        AllocatedType* used_;
        AllocatedType* end_;
        AllocatedType buffer_[objectPerAllocation];
    };

    // disabled copy constructor and assignement operator.
    BatchAllocator ( const BatchAllocator& );
    void operator = ( const BatchAllocator&);

    static BatchInfo* allocateBatch ( unsigned int objectsPerPage )
    {
        const unsigned int mallocSize = sizeof (BatchInfo) - sizeof (AllocatedType) * objectPerAllocation
                                        + sizeof (AllocatedType) * objectPerAllocation * objectsPerPage;
        BatchInfo* batch = static_cast<BatchInfo*> ( malloc ( mallocSize ) );
        batch->next_ = 0;
        batch->used_ = batch->buffer_;
        batch->end_ = batch->buffer_ + objectsPerPage;
        return batch;
    }

    BatchInfo* batches_;
    BatchInfo* currentBatch_;
    /// Head of a single linked list within the allocated space of freeed object
    AllocatedType* freeHead_;
    unsigned int objectsPerPage_;
};


} // namespace Json

# endif // ifndef JSONCPP_DOC_INCLUDE_IMPLEMENTATION

#endif // JSONCPP_BATCHALLOCATOR_H_INCLUDED