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#ifndef JSONCPP_BATCHALLOCATOR_H_INCLUDED |
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# define JSONCPP_BATCHALLOCATOR_H_INCLUDED |
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|
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# include <stdlib.h> |
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# include <assert.h> |
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|
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# ifndef JSONCPP_DOC_EXCLUDE_IMPLEMENTATION |
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|
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namespace Json { |
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|
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/* Fast memory allocator. |
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* |
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* This memory allocator allocates memory for a batch of object (specified by |
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* the page size, the number of object in each page). |
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* |
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* It does not allow the destruction of a single object. All the allocated objects |
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* can be destroyed at once. The memory can be either released or reused for future |
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* allocation. |
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* |
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* The in-place new operator must be used to construct the object using the pointer |
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* returned by allocate. |
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*/ |
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template<typename AllocatedType |
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,const unsigned int objectPerAllocation> |
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class BatchAllocator |
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{ |
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public: |
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typedef AllocatedType Type; |
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|
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BatchAllocator( unsigned int objectsPerPage = 255 ) |
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: freeHead_( 0 ) |
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, objectsPerPage_( objectsPerPage ) |
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{ |
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// printf( "Size: %d => %s\n", sizeof(AllocatedType), typeid(AllocatedType).name() ); |
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assert( sizeof(AllocatedType) * objectPerAllocation >= sizeof(AllocatedType *) ); // We must be able to store a slist in the object free space. |
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assert( objectsPerPage >= 16 ); |
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batches_ = allocateBatch( 0 ); // allocated a dummy page |
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currentBatch_ = batches_; |
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} |
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|
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~BatchAllocator() |
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{ |
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for ( BatchInfo *batch = batches_; batch; ) |
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{ |
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BatchInfo *nextBatch = batch->next_; |
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free( batch ); |
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batch = nextBatch; |
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} |
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} |
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|
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/// allocate space for an array of objectPerAllocation object. |
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/// @warning it is the responsability of the caller to call objects constructors. |
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AllocatedType *allocate() |
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{ |
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if ( freeHead_ ) // returns node from free list. |
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{ |
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AllocatedType *object = freeHead_; |
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freeHead_ = *(AllocatedType **)object; |
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return object; |
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} |
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if ( currentBatch_->used_ == currentBatch_->end_ ) |
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{ |
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currentBatch_ = currentBatch_->next_; |
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while ( currentBatch_ && currentBatch_->used_ == currentBatch_->end_ ) |
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currentBatch_ = currentBatch_->next_; |
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|
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if ( !currentBatch_ ) // no free batch found, allocate a new one |
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{ |
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currentBatch_ = allocateBatch( objectsPerPage_ ); |
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currentBatch_->next_ = batches_; // insert at the head of the list |
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batches_ = currentBatch_; |
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} |
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} |
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AllocatedType *allocated = currentBatch_->used_; |
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currentBatch_->used_ += objectPerAllocation; |
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return allocated; |
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} |
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|
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/// Release the object. |
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/// @warning it is the responsability of the caller to actually destruct the object. |
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void release( AllocatedType *object ) |
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{ |
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assert( object != 0 ); |
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*(AllocatedType **)object = freeHead_; |
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freeHead_ = object; |
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} |
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|
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private: |
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struct BatchInfo |
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{ |
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BatchInfo *next_; |
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AllocatedType *used_; |
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AllocatedType *end_; |
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AllocatedType buffer_[objectPerAllocation]; |
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}; |
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|
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// disabled copy constructor and assignement operator. |
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BatchAllocator( const BatchAllocator & ); |
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void operator =( const BatchAllocator &); |
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|
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static BatchInfo *allocateBatch( unsigned int objectsPerPage ) |
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{ |
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const unsigned int mallocSize = sizeof(BatchInfo) - sizeof(AllocatedType)* objectPerAllocation |
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+ sizeof(AllocatedType) * objectPerAllocation * objectsPerPage; |
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BatchInfo *batch = static_cast<BatchInfo*>( malloc( mallocSize ) ); |
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batch->next_ = 0; |
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batch->used_ = batch->buffer_; |
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batch->end_ = batch->buffer_ + objectsPerPage; |
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return batch; |
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} |
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|
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BatchInfo *batches_; |
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BatchInfo *currentBatch_; |
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/// Head of a single linked list within the allocated space of freeed object |
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AllocatedType *freeHead_; |
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unsigned int objectsPerPage_; |
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}; |
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|
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|
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} // namespace Json |
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|
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# endif // ifndef JSONCPP_DOC_INCLUDE_IMPLEMENTATION |
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|
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#endif // JSONCPP_BATCHALLOCATOR_H_INCLUDED |
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