126 lines
3.8 KiB
C++
126 lines
3.8 KiB
C++
#ifndef JSONCPP_BATCHALLOCATOR_H_INCLUDED
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# define JSONCPP_BATCHALLOCATOR_H_INCLUDED
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# include <stdlib.h>
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# include <assert.h>
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# ifndef JSONCPP_DOC_EXCLUDE_IMPLEMENTATION
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namespace Json {
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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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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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~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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/// 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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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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/// 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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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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// 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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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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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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} // namespace Json
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# endif // ifndef JSONCPP_DOC_INCLUDE_IMPLEMENTATION
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#endif // JSONCPP_BATCHALLOCATOR_H_INCLUDED
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