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-rw-r--r--src/leveldb/util/arena.cc68
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diff --git a/src/leveldb/util/arena.cc b/src/leveldb/util/arena.cc
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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.
+
+#include "util/arena.h"
+#include <assert.h>
+
+namespace leveldb {
+
+static const int kBlockSize = 4096;
+
+Arena::Arena() {
+ blocks_memory_ = 0;
+ alloc_ptr_ = NULL; // First allocation will allocate a block
+ alloc_bytes_remaining_ = 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*); // We'll align to pointer size
+ 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_memory_ += block_bytes;
+ blocks_.push_back(result);
+ return result;
+}
+
+} // namespace leveldb