src/leveldb/util/arena.h

   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 #ifndef STORAGE_LEVELDB_UTIL_ARENA_H_
   6 #define STORAGE_LEVELDB_UTIL_ARENA_H_
   7
   8 #include <vector>
   9 #include <assert.h>
  10 #include <stddef.h>
  11 #include <stdint.h>
  12 #include "port/port.h"
  13
  14 namespace leveldb {
  15
  16 class Arena {
  17  public:
  18   Arena();
  19   ~Arena();
  20
  21   // Return a pointer to a newly allocated memory block of "bytes" bytes.
  22   char* Allocate(size_t bytes);
  23
  24   // Allocate memory with the normal alignment guarantees provided by malloc
  25   char* AllocateAligned(size_t bytes);
  26
  27   // Returns an estimate of the total memory usage of data allocated
  28   // by the arena.
  29   size_t MemoryUsage() const {
  30     return reinterpret_cast<uintptr_t>(memory_usage_.NoBarrier_Load());
  31   }
  32
  33  private:
  34   char* AllocateFallback(size_t bytes);
  35   char* AllocateNewBlock(size_t block_bytes);
  36
  37   // Allocation state
  38   char* alloc_ptr_;
  39   size_t alloc_bytes_remaining_;
  40
  41   // Array of new[] allocated memory blocks
  42   std::vector<char*> blocks_;
  43
  44   // Total memory usage of the arena.
  45   port::AtomicPointer memory_usage_;
  46
  47   // No copying allowed
  48   Arena(const Arena&);
  49   void operator=(const Arena&);
  50 };
  51
  52 inline char* Arena::Allocate(size_t bytes) {
  53   // The semantics of what to return are a bit messy if we allow
  54   // 0-byte allocations, so we disallow them here (we don't need
  55   // them for our internal use).
  56   assert(bytes > 0);
  57   if (bytes <= alloc_bytes_remaining_) {
  58     char* result = alloc_ptr_;
  59     alloc_ptr_ += bytes;
  60     alloc_bytes_remaining_ -= bytes;
  61     return result;
  62   }
  63   return AllocateFallback(bytes);
  64 }
  65
  66 }  // namespace leveldb
  67
  68 #endif  // STORAGE_LEVELDB_UTIL_ARENA_H_