You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
66 lines
2.0 KiB
66 lines
2.0 KiB
// 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.
|
|
|
|
#include "util/arena.h"
|
|
|
|
namespace leveldb {
|
|
|
|
static const int kBlockSize = 4096;
|
|
|
|
Arena::Arena()
|
|
: alloc_ptr_(nullptr), alloc_bytes_remaining_(0), memory_usage_(0) {}
|
|
|
|
Arena::~Arena() {
|
|
for (size_t i = 0; i < blocks_.size(); i++) {
|
|
delete[] blocks_[i];
|
|
}
|
|
}
|
|
|
|
char* Arena::AllocateFallback(size_t bytes) {
|
|
if (bytes > kBlockSize / 4) {
|
|
// Object is more than a quarter of our block size. Allocate it separately
|
|
// to avoid wasting too much space in leftover bytes.
|
|
char* result = AllocateNewBlock(bytes);
|
|
return result;
|
|
}
|
|
|
|
// We waste the remaining space in the current block.
|
|
alloc_ptr_ = AllocateNewBlock(kBlockSize);
|
|
alloc_bytes_remaining_ = kBlockSize;
|
|
|
|
char* result = alloc_ptr_;
|
|
alloc_ptr_ += bytes;
|
|
alloc_bytes_remaining_ -= bytes;
|
|
return result;
|
|
}
|
|
|
|
char* Arena::AllocateAligned(size_t bytes) {
|
|
const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
|
|
static_assert((align & (align - 1)) == 0,
|
|
"Pointer size should be a power of 2");
|
|
size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align - 1);
|
|
size_t slop = (current_mod == 0 ? 0 : align - current_mod);
|
|
size_t needed = bytes + slop;
|
|
char* result;
|
|
if (needed <= alloc_bytes_remaining_) {
|
|
result = alloc_ptr_ + slop;
|
|
alloc_ptr_ += needed;
|
|
alloc_bytes_remaining_ -= needed;
|
|
} else {
|
|
// AllocateFallback always returned aligned memory
|
|
result = AllocateFallback(bytes);
|
|
}
|
|
assert((reinterpret_cast<uintptr_t>(result) & (align - 1)) == 0);
|
|
return result;
|
|
}
|
|
|
|
char* Arena::AllocateNewBlock(size_t block_bytes) {
|
|
char* result = new char[block_bytes];
|
|
blocks_.push_back(result);
|
|
memory_usage_.fetch_add(block_bytes + sizeof(char*),
|
|
std::memory_order_relaxed);
|
|
return result;
|
|
}
|
|
|
|
} // namespace leveldb
|