1. Customizing Run Management
Makoto Asai (SLAC)
Geant4 Users CERN
Nov. 15th, 2002

2. Contents G4RunManager Basic flow of Geant4 kernel
Structure of G4RunManager
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

3. G4RunManager
G4RunManager is the only manager class in Geant4 kernel from which the user is allowed / expected to inherit and create his / her own customized manager.
For large HEP experiments, it is rather mandatory to make their own customized managers.
For connecting to their specific frameworks
For their persistency solutions
Etc.
G4RunManager is well structured and almost all of its methods are virtual.
Thus the user can easily overwrite some of its methods for customization while keep utilizing other methods given in the base class.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

4. How Geant4 runs w.r.t. run management
Instantiation
Instantiation / initialization of manager classes
Initialization
Construction of material and geometry
Construction of particles, physics processes
Calculation of cross-section tables
“Beam-On” = “Run”
Close geometry --> Optimize geometry
Event Loop
Termination
Deletion of manager classes
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

5. User classes Initialization classes - Invoked at the initialization
G4VUserDetectorConstruction
G4VUserPhysicsList
Action classes - Invoked during the event loop
G4VUserPrimaryGeneratorAction
G4UserRunAction
G4UserEventAction
G4UserStackingAction
G4UserTrackingAction
G4UserSteppingAction
Classes with yellow underlines are “mandatory’ classes.
Classes written in red are used directly by G4RunManager.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

6. G4ApplicationState
Geant4 is a state machine. It has seven states, PreInit, Init, Idle, GeomClosed, EventProc, Quit and Abort.
All state changes except Abort are triggered by G4RunManager.
Abort state is triggered by G4Exception.
Note that the state of Geant4 is always EventProc while an event is processing.
Other five states (PreInit, Init, Idle, GeomClosed and Quit) are for the sake of proper handling of run management.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

7. Constructor / destructor of G4RunManager
G4RunManager::G4RunManager()
Instantiation and initialization of kernel manager classes
G4RunManager::~G4RunManager()
Deletion of kernel manager classes
Orders of instantiation and deletion of kernel manager classes are important to avoid conflicts.
By deriving G4RunManager, these constructor and destructor are used to ensure the correct ordering.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

8. Methods in G4RunManager for initialization
virtual void Initialize();
This method invokes all the necessary initialization procedures.
This method invokes three granular methods, InitializeGeometry(), InitializePhysics() and InitializeCutOff().
After some event loops, the user can invoke this method once again.
It is rather mandatory if the user changes geometry, physics process, and/or cut off value(s).
If the user forget the second invokation, G4RunManager will automatically invoke this method at the moment of next BeamOn.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

9. Methods in G4RunManager for initialization
virtual void InitializeGeometry();
This method invokes user’s concrete G4VUserDetectorConstruction::Construct().
Then the world volume is set to G4Navigator through G4RunManager::DefineWorldVolume() method.
Note that all materials must be constructed before start calculating cross-section tables.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

10. Methods in G4RunManager for initialization
virtual void InitializePhysics();
This method invokes user’s G4VUserPhysicsList::Construct().
Note that all particles must be defined and all processes must be properly assigned to them before start calculating cross-section tables.
virtual void InitializeCutOff();
This method invokes user’s G4VUserPhysicsList::SetCut() to calculate cross-section tables.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

11. Methods in G4RunManager for event loop
virtual void BeamOn();
This method starts an event loop. The condition of Geant4 is examined before starting the event loop.
This method invokes four granular methods, ConfirmBeamOnCondition(), RunInitialization(), DoEventLoop() and RunTermination().
According to the second and third arguments of BeamOn method, a macro file will be read at the end of each event.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

12. Methods in G4RunManager for event loop
virtual G4bool ConfirmBeamOnCondition();
Confirms initialization, re-initialization if needed
virtual void RunInitialization();
Closes geometry
virtual void DoEventLoop();
Manages an event loop
Invokes two granular methods, GenerateEvent() and AnalyzeEvent() for each event
virtual void RunTermination();
Opens geometry
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

13. Methods in G4RunManager for one event
virtual G4event* GenerateEvent();
Instantiates G4Event object
Invokes user’s G4VUserPrimaryGeneratorAction
virtual void AnalyzeEvent();
Basically does nothing as default
Invokes G4VPersistencyManager if the user defines a concrete class
Allows access to more than one events for, for example, event pile-up.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

14. Future plans
We believe G4RunManager is well modularized for most of the cases.
So that the user can easily derive his/her own concrete (customized) RunManager by just overwriting some of its virtual methods.
G4RunManager contains both some mandatory procedures to use Geant4 kernel and also some utility functionalities to make the user easy to use Geant4.
We understand there exists a requirement from CMS to split mandatory procedures from utilities.
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)

15. Future plans
To meet this requirement from CMS, we are studying to split G4RunManager into three classes.
G4RunManager
Keeps all methods in its header file so that ordinary users do not need to change anything
Is to be re-implemented to use following two classes
G4RunManagerCore
Has all mandatory procedures to use Geant4 kernel
G4RunManagerUtilities
Has most of utility functionalities which the current G4RunManager has, and which are still useful to experienced users
Customizing Run Management - M.Asai (SLAC) - Geant4 Users CERN (Nov/15/2002)