68 行
1.7 KiB

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