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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
// ArenaImpl is an implementation of Arena class. For a request of small size,
// it allocates a block with pre-defined block size. For a request of big
// size, it uses malloc to directly get the requested size.
#ifndef STORAGE_LEVELDB_UTIL_ARENA_IMPL_H_
#define STORAGE_LEVELDB_UTIL_ARENA_IMPL_H_
#include <cstddef>
#include <vector>
#include <assert.h>
#include <stdint.h>
#include "rocksdb/arena.h"
namespace leveldb {
class ArenaImpl : public Arena {
public:
explicit ArenaImpl(size_t block_size = kMinBlockSize);
virtual ~ArenaImpl();
virtual char* Allocate(size_t bytes);
virtual char* AllocateAligned(size_t bytes);
// Returns an estimate of the total memory usage of data allocated
// by the arena (including space allocated but not yet used for user
// allocations).
//
// TODO: Do we need to exclude space allocated but not used?
virtual const size_t ApproximateMemoryUsage() {
return blocks_memory_ + blocks_.capacity() * sizeof(char*);
}
virtual const size_t MemoryAllocatedBytes() {
return blocks_memory_;
}
private:
char* AllocateFallback(size_t bytes);
char* AllocateNewBlock(size_t block_bytes);
static const size_t kMinBlockSize = 4096;
static const size_t kMaxBlockSize = 2 << 30;
// Number of bytes allocated in one block
size_t block_size_;
// Allocation state
char* alloc_ptr_;
size_t alloc_bytes_remaining_;
// Array of new[] allocated memory blocks
std::vector<char*> blocks_;
// Bytes of memory in blocks allocated so far
size_t blocks_memory_;
// No copying allowed
ArenaImpl(const ArenaImpl&);
void operator=(const ArenaImpl&);
};
inline char* ArenaImpl::Allocate(size_t bytes) {
// The semantics of what to return are a bit messy if we allow
// 0-byte allocations, so we disallow them here (we don't need
// them for our internal use).
assert(bytes > 0);
if (bytes <= alloc_bytes_remaining_) {
char* result = alloc_ptr_;
alloc_ptr_ += bytes;
alloc_bytes_remaining_ -= bytes;
return result;
}
return AllocateFallback(bytes);
}
} // namespace leveldb
#endif // STORAGE_LEVELDB_UTIL_ARENA_IMPL_H_
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