ceph/src/rocksdb/include/rocksdb/write_buffer_manager.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under the BSD-style license found in the
   3 //  LICENSE file in the root directory of this source tree. An additional grant
   4 //  of patent rights can be found in the PATENTS file in the same directory.
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9 //
  10 // WriteBufferManager is for managing memory allocation for one or more
  11 // MemTables.
  12
  13 #pragma once
  14
  15 #include <atomic>
  16 #include <cstddef>
  17
  18 namespace rocksdb {
  19
  20 class WriteBufferManager {
  21  public:
  22   // _buffer_size = 0 indicates no limit. Memory won't be tracked,
  23   // memory_usage() won't be valid and ShouldFlush() will always return true.
  24   explicit WriteBufferManager(size_t _buffer_size)
  25       : buffer_size_(_buffer_size), memory_used_(0) {}
  26
  27   ~WriteBufferManager() {}
  28
  29   bool enabled() const { return buffer_size_ != 0; }
  30
  31   // Only valid if enabled()
  32   size_t memory_usage() const {
  33     return memory_used_.load(std::memory_order_relaxed);
  34   }
  35   size_t buffer_size() const { return buffer_size_; }
  36
  37   // Should only be called from write thread
  38   bool ShouldFlush() const {
  39     return enabled() && memory_usage() >= buffer_size();
  40   }
  41
  42   // Should only be called from write thread
  43   void ReserveMem(size_t mem) {
  44     if (enabled()) {
  45       memory_used_.fetch_add(mem, std::memory_order_relaxed);
  46     }
  47   }
  48   void FreeMem(size_t mem) {
  49     if (enabled()) {
  50       memory_used_.fetch_sub(mem, std::memory_order_relaxed);
  51     }
  52   }
  53
  54  private:
  55   const size_t buffer_size_;
  56   std::atomic<size_t> memory_used_;
  57
  58   // No copying allowed
  59   WriteBufferManager(const WriteBufferManager&) = delete;
  60   WriteBufferManager& operator=(const WriteBufferManager&) = delete;
  61 };
  62 }  // namespace rocksdb