122 lines
3.9 KiB
C++
122 lines
3.9 KiB
C++
// Copyright 2007-2010 Baptiste Lepilleur
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// Distributed under MIT license, or public domain if desired and
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// recognized in your jurisdiction.
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// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
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#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
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* objects can be destroyed at once. The memory can be either released or reused
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* for future allocation.
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*
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* The in-place new operator must be used to construct the object using the
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* pointer returned by allocate.
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*/
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template <typename AllocatedType, const unsigned int objectPerAllocation>
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class BatchAllocator {
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public:
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BatchAllocator(unsigned int objectsPerPage = 255)
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: freeHead_(0), objectsPerPage_(objectsPerPage) {
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// printf( "Size: %d => %s\n", sizeof(AllocatedType),
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// typeid(AllocatedType).name() );
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assert(sizeof(AllocatedType) * objectPerAllocation >=
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sizeof(AllocatedType*)); // We must be able to store a slist in the
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// 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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for (BatchInfo* batch = batches_; batch;) {
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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
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/// constructors.
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AllocatedType* allocate() {
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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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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
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/// object.
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void release(AllocatedType* object) {
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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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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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const unsigned int mallocSize =
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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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