Line data    Source code

       1             : // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file. See the AUTHORS file for names of contributors.
       4             : 
       5             : #include "util/arena.h"
       6             : #include <assert.h>
       7             : 
       8             : namespace leveldb {
       9             : 
      10             : static const int kBlockSize = 4096;
      11             : 
      12         359 : Arena::Arena() {
      13         359 :   blocks_memory_ = 0;
      14         359 :   alloc_ptr_ = NULL;  // First allocation will allocate a block
      15         359 :   alloc_bytes_remaining_ = 0;
      16         359 : }
      17             : 
      18         718 : Arena::~Arena() {
      19        3020 :   for (size_t i = 0; i < blocks_.size(); i++) {
      20        2302 :     delete[] blocks_[i];
      21             :   }
      22         359 : }
      23             : 
      24        1151 : char* Arena::AllocateFallback(size_t bytes) {
      25        1151 :   if (bytes > kBlockSize / 4) {
      26             :     // Object is more than a quarter of our block size.  Allocate it separately
      27             :     // to avoid wasting too much space in leftover bytes.
      28           5 :     char* result = AllocateNewBlock(bytes);
      29           5 :     return result;
      30             :   }
      31             : 
      32             :   // We waste the remaining space in the current block.
      33        1146 :   alloc_ptr_ = AllocateNewBlock(kBlockSize);
      34        1146 :   alloc_bytes_remaining_ = kBlockSize;
      35             : 
      36        1146 :   char* result = alloc_ptr_;
      37        1146 :   alloc_ptr_ += bytes;
      38        1146 :   alloc_bytes_remaining_ -= bytes;
      39        1146 :   return result;
      40             : }
      41             : 
      42       28908 : char* Arena::AllocateAligned(size_t bytes) {
      43       28908 :   const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
      44             :   assert((align & (align-1)) == 0);   // Pointer size should be a power of 2
      45       28908 :   size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
      46       28908 :   size_t slop = (current_mod == 0 ? 0 : align - current_mod);
      47       28908 :   size_t needed = bytes + slop;
      48             :   char* result;
      49       28908 :   if (needed <= alloc_bytes_remaining_) {
      50       28509 :     result = alloc_ptr_ + slop;
      51       28509 :     alloc_ptr_ += needed;
      52       28509 :     alloc_bytes_remaining_ -= needed;
      53             :   } else {
      54             :     // AllocateFallback always returned aligned memory
      55         399 :     result = AllocateFallback(bytes);
      56             :   }
      57       28908 :   assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
      58       28908 :   return result;
      59             : }
      60             : 
      61        1151 : char* Arena::AllocateNewBlock(size_t block_bytes) {
      62        1151 :   char* result = new char[block_bytes];
      63        1151 :   blocks_memory_ += block_bytes;
      64        1151 :   blocks_.push_back(result);
      65        1151 :   return result;
      66             : }
      67             : 
      68             : }  // namespace leveldb