tlbmc/hal/shared_mem/segment_manager.h

#ifndef THIRD_PARTY_MILOTIC_EXTERNAL_CC_TLBMC_HAL_SHARED_MEM_SEGMENT_MANAGER_H_
#define THIRD_PARTY_MILOTIC_EXTERNAL_CC_TLBMC_HAL_SHARED_MEM_SEGMENT_MANAGER_H_

#include <memory>
#include <string_view>
#include <utility>

#include "boost/interprocess/managed_shared_memory.hpp"  // NOLINT
#include "tlbmc/hal/shared_mem/metrics.h"
#include "tlbmc/hal/shared_mem/sensors.h"

namespace milotic_tlbmc {

constexpr std::string_view kShareMemInitializedFile =
    "/run/tlbmc/shm_initialized";

// The class is thread-safe.
class SegmentManager {
 public:
  virtual ~SegmentManager() = default;

  // Reads `initialized_file_path` to check if the shared memory is
  // initialized. If not, creates the shared memory and touches the file.
  // Returns nullptr on errors.
  // This API shall only be called by the server (tlbmc).
  static std::unique_ptr<SegmentManager> Create(
      std::string_view initialized_file_path = kShareMemInitializedFile);

  // Returns the shared memory segment.
  // This API shall only be called by clients (telemetry daemons).
  static std::unique_ptr<SegmentManager> Get(
      std::string_view initialized_file_path = kShareMemInitializedFile);

  // Returns the sensor with the given name. If the sensor does not exist,
  // creates the sensor.
  // This API is very expensive. Callers should cache the returned pointer.
  virtual IpcSensor* GetOrCreateSensor(const char* sensor_name);

  // Returns the metrics. If the metrics does not exist, creates the metrics.
  // This API is very expensive. Callers should cache the returned pointer.
  virtual TlbmcMetrics* GetOrCreateMetrics();

 protected:
  SegmentManager() = default;

  static std::unique_ptr<SegmentManager> CreateHelper(
      std::string_view initialized_file_path);

  boost::interprocess::managed_shared_memory& GetMemory() { return memory_; }

 private:
  explicit SegmentManager(boost::interprocess::managed_shared_memory&& memory)
      : memory_(std::move(memory)) {}
  boost::interprocess::managed_shared_memory memory_;
};

// A dummy segment manager that does nothing.
// This is used when the shared memory is not available due to system error or
// library error.
class SegmentManagerDummy : public SegmentManager {
 public:
  SegmentManagerDummy() = default;
  IpcSensor* GetOrCreateSensor(
      [[maybe_unused]] const char* sensor_name) override {
    return nullptr;
  }
  TlbmcMetrics* GetOrCreateMetrics() override { return nullptr; }
};

}  // namespace milotic_tlbmc

#endif  // THIRD_PARTY_MILOTIC_EXTERNAL_CC_TLBMC_HAL_SHARED_MEM_SEGMENT_MANAGER_H_