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// Copyright 2007-2010 Baptiste Lepilleur
// Distributed under MIT license, or public domain if desired and
// recognized in your jurisdiction.
// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
#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:
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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