MagneticField.h

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#ifndef MagneticField_MagneticField_h
#define MagneticField_MagneticField_h

#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "FWCore/Utilities/interface/Visibility.h"
#include "FWCore/Utilities/interface/Likely.h"
#include <atomic>

class MagneticField
{
 public:
  MagneticField();
  MagneticField(const MagneticField& orig);
  virtual ~MagneticField();

  virtual MagneticField* clone() const {
    return nullptr;
  }
  
  virtual GlobalVector inTesla (const GlobalPoint& gp) const = 0;

  GlobalVector inKGauss(const GlobalPoint& gp) const  {
    return inTesla(gp) * 10.F;
  }

  GlobalVector inInverseGeV(const GlobalPoint& gp) const {
    return inTesla(gp) * 2.99792458e-3F;
  }

  // engine is defined.
  virtual bool isDefined(const GlobalPoint& /*gp*/) const {
    return true;
  }
  
  virtual GlobalVector inTeslaUnchecked (const GlobalPoint& gp) const {
    return inTesla(gp);  // default dummy implementation
  }
  
  int nominalValue() const {  
     if(kSet==nominalValueCompiuted.load()) return theNominalValue;
     return computeNominalValue();
  }     

private:
  //nominal field value 
  virtual int computeNominalValue() const;
  mutable std::atomic<char> nominalValueCompiuted;
//  [[cms::thread_guard("nominalValueCompiuted")]] mutable int theNominalValue;
//  PG temporary fix for clang 3.4 which is not parsing thread_guard correctly
  [[cms::thread_safe]] mutable int theNominalValue;
  enum FooStates {kUnset, kSetting, kSet};
};

#endif