ReadBuffer.h

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#ifndef FWCore_SharedMemory_ReadBuffer_h
#define FWCore_SharedMemory_ReadBuffer_h
// -*- C++ -*-
//
// Package:     FWCore/SharedMemory
// Class  :     ReadBuffer
//
//
// Original Author:  Chris Jones
//         Created:  21/01/2020
//

// system include files
#include <array>
#include <memory>
#include <string>
#include "boost/interprocess/managed_shared_memory.hpp"

// user include files
#include "FWCore/SharedMemory/interface/buffer_names.h"
#include "FWCore/SharedMemory/interface/BufferInfo.h"

// forward declarations

namespace edm::shared_memory {
  class ReadBuffer {
  public:
    ReadBuffer(std::string const& iUniqueName, BufferInfo* iBufferInfo)
        : buffer_{nullptr, 0}, bufferInfo_{iBufferInfo}, bufferOldIndex_{3} {
      *bufferInfo_ = {0, 0};
      bufferNames_[0] = iUniqueName + buffer_names::kBuffer0;
      bufferNames_[1] = iUniqueName + buffer_names::kBuffer1;
    }
    ReadBuffer(const ReadBuffer&) = delete;
    const ReadBuffer& operator=(const ReadBuffer&) = delete;
    ReadBuffer(ReadBuffer&&) = delete;
    const ReadBuffer& operator=(ReadBuffer&&) = delete;

    // ---------- const member functions ---------------------
    int bufferIdentifier() const { return bufferInfo_->identifier_; }

    // ---------- member functions ---------------------------
    std::pair<char*, std::size_t> buffer() {
      if (mustGetBufferAgain()) {
        using namespace boost::interprocess;
        sm_ = std::make_unique<managed_shared_memory>(open_only, bufferNames_[bufferInfo_->index_].c_str());
        buffer_ = sm_->find<char>(buffer_names::kBuffer);
        bufferOldIndex_ = bufferInfo_->index_;
      }
      return buffer_;
    }

  private:
    bool mustGetBufferAgain() const { return bufferInfo_->index_ != bufferOldIndex_; }
    // ---------- member data --------------------------------
    std::pair<char*, std::size_t> buffer_;
    BufferInfo* bufferInfo_;
    char bufferOldIndex_;
    std::array<std::string, 2> bufferNames_;
    std::unique_ptr<boost::interprocess::managed_shared_memory> sm_;
  };
}  // namespace edm::shared_memory

#endif