VMCSeederService.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
#ifndef ALICEO2_VMC_SEEDERSERVICE_H
#define ALICEO2_VMC_SEEDERSERVICE_H
 
class TVirtualMC;
class TRandom;
 
#include <atomic>
#include <functional>
 
namespace o2
{
namespace base
{
 
// A simple (singleton) service to propagate random number seeding
// to VMC engines in a loosely-coupled, just-in-time way (without needing to compile against these libraries).
class VMCSeederService
{
 
 public:
  static VMCSeederService const& instance()
  {
    static VMCSeederService inst;
    return inst;
  }
 
  void setSeed() const; // will propagate the seed of o2::base::simRandom() to the VMC engine of this thread
 
  unsigned long long getSeedCount() const { return mSeedCount; }
 
  typedef std::function<void(TRandom*)> SeederFcn;
 
  static void setGeant4Seeder(SeederFcn fcn) { geant4Seeder() = std::move(fcn); }
 
 private:
  VMCSeederService();
  static SeederFcn& geant4Seeder()
  {
    static SeederFcn fcn;
    return fcn;
  }
  void initSeederFunction(TVirtualMC const*);
 
  SeederFcn mSeederFcn;                                  // the function talking to the VMC engine
  mutable std::atomic<unsigned long long> mSeedCount{0}; // number of setSeed() calls
};
 
} // namespace base
} // namespace o2
 
#endif