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#ifndef JSONCPP_BATCHALLOCATOR_H_INCLUDED
# define JSONCPP_BATCHALLOCATOR_H_INCLUDED
# include <stdlib.h>
# include <assert.h>
# 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
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