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Proxy Mechanism of BESF

Learn about the implementation, processing, and examples of the proxy mechanism in the BESF framework, allowing for efficient data management and object access.

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Proxy Mechanism of BESF

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  1. Proxy Mechanism of BESF ZhangxyHuangxt Dec 17 ,2003

  2. Content • Introduction. • Implementation. • Processing. • Example. • Summary

  3. Introduction • Proxy is another way of data management system in our • BesIII framework(BESF), learned from BABAR. • The separation of Transient Event and Persistent Event is • commonly used in other frameworks. • If the object associated with the Transient Event exists, Clients can get it directly from proxy.

  4. Introduction • If the object does’t exist, Proxy can create and then return it to Clients by calling its member function : virtual T*  faultHandler ( IfdProxyDict *, const IfdKey & ); • Proxy can put and get objects from the Transient Event in a type_safe fashion by virtue of template , hash table and wrap mechanism.

  5. Implementation • Transient Object • Proxy Interface • Proxy Dictionary • Keys • Accessor

  6. Implementation • Transient Object • Single instance • The class must inherit from BesDataObject. • Multi-instances • The class must inherit from BesContainedObject. m_parent BesObjectContainedBase BesObjectList<T> BesObjectVector<T>

  7. Implementation • Proxy Interface • Single object proxy T *ifdl = new T; IfdDataProxy<T> *proxy = new IfdDataProxy<T>( ifdl );

  8. Implementation • List object proxy BesObjectList<T> *ifdl = new BesObjectList<T>; BesObjectListProxy<T> *proxy = new BesObjectListProxy<T>( ifdl );

  9. Implementation • Above action has been done automatically by • BesEvent member function.Clients only need to • define the argument of the template functions. bool put( const IfdDictKey* key, IfdProxyIFace* proxy); template<class T> void  GetObjList (BesObjectVector< T > *&list); template<class T> void  GetObjList (BesObjectVector< T > *&list, const IfdKey &k); template<class T> void  GetObjList (BesObjectList< T > *&list); template<class T> void  GetObjList (BesObjectList< T > *&list, const IfdKey &k); template<class T> void  GetObj (T *&obj); template<class T> void  GetObj (T *&obj, const IfdKey &k); void clear();

  10. Implementation • Proxy Dictionary • The transient event store is implemented with Proxy Dictionary. • The Proxy Dictionary is implemented with a hash table and singly linked list. 1031

  11. Implementation • Access “object” from Dictionary • according to the hash value or • recursive comparison. • The hash value is given by the keys • BesEvent is a instance of the Dictionary.

  12. Implementation • Keys • In order to select the wanted object when • multiple instances of objects from the same • class “stored” in BesEvent or Proxy Dictionary. • Collision • Composite Key + Move Bit + Mod()

  13. The integer keys and string keys are interested for • clients, while other keys are used automatically.

  14. Implementation • Accessor • Ifd<T> class provides only and • type-safe access to the objects or • lists within BesEvent. • Identified by a key or characters to differentiate • them from other instances of the same class.

  15. Processing BesEventHeader* header = new BesaEventHeader(); first typekey proxy IfdDataProxy<BesEventHeader> *proxy = new IfdDataProxy<BesEventHeader>( header ); dictkey true Find() false next put

  16. Processing 1. Get the object from Transient event identified with string. T* Ifd<T>::Get(IfdProxyDict * Dict, const char* str) 2. Create valid Key. IfdstrKey k(str); 3. Call another member funtion. T* Ifd<T>::Get(IfdProxyDict* Dict, const IfdKey &K); 4. Create TypeKey and composite Key,that’s , Dictionary Key. static IfdTypeKey<Ifd<T> > tk; static IfdDictKey* dictkey=IfdProxyDictFrontEnd::newDictKey( tk); dictKey -> add( K); 5. Get the object according dictkey. (T*) Dict -> get( dictKey ) 6. Find the Proxy IfdProxyIface *p = Dict -> find( dictkey);

  17. Processing 7. Find the ProxyEntry. IfdSimpleProxyDictEntry *e = Dict -> findEntry( dictkey ); 8. Recursive Comparison. IfSimpleProxyDictEntry* e = _myData[dictkey._hashVal]; if ( 0==e) { return 0;} else if ( *e->key == dictkey ) { return e; } else while ( 0 != (e=e->next ) ) { if (*e->key == k) { return e;} } 9 Return object wanted return p->_myt; return T* t=p->defaulthandler(Dict, dictKey);

  18. Example • BESF makes the transient event available to BesMoudles • as an argument to the following member function: • virtual BesStatusExecute ( BesEvent *evt, Int_t *status) • virtual void  event ( BesEvent *evt, Int_t *status) • Clients can conveniently get objects from BesEvent. void NDSTunpackModule::event ( BesEvent * anEvent, int * status ) { NDSTtrack * aTrack ; NDSTEventHeader *eventPtr ; BesObjectVector<NDSTtrack>* trklist; anEvent->GetObjList( trklist ); anEvent->GetObj( eventPtr ); …… }

  19. Summary • Simple and type safe. • Easier to use than others.

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