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StoreGate Data Management Tutorial for CERN Users

This tutorial provides a comprehensive guide on accessing and managing data with StoreGate at CERN. Learn how to record and retrieve data objects by type, utilize keys for object identification, and explore inter-object relationships. The tutorial covers essential functionalities including recording keyless objects, locking data objects, and retrieving data collections. Whether you're setting up your environment or implementing algorithms like SGWrite and SGRead, this guide is designed for efficient data handling in the Athena framework.

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StoreGate Data Management Tutorial for CERN Users

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  1. StoreGate Tutorial March 8, 2002 CERN

  2. Outline • TDS access using StoreGate • record/retrieve by TYPE • Data Objects can be keyed in SG • Retrieval of all data objects of a given type • Data Links • Inter-Object relationships

  3. Preliminaries:Accessing StoreGate • StoreGateSvc is the Gaudi service that allows to record and retrieve data objects. • Obtain the pointer to the StoreGateSvc: In the initialize method of your algorithm: StatusCode sc = service(“StoreGateSvc”, m_storeGate); declare m_storeGate as a private data member of type StoreGateSvc* This caches m_storeGate and you do not have to call the serviceLocator to retrieve the pointer to StoreGateSvc every event in your execute method.

  4. Recording an Object • Providing a Key: StatusCode sc = m_storeGate record(TrkColl, TrkCollName); • where : • TrkColl is a pointer to your TrackCollection (a DataObject) • TrkCollName is an identifying name for your data object also specified in your jobOptions in a similar way. It can be something like: “MyTrackCollection” • Keyless: StatusCode sc = m_storeGate record(TrkColl); • Locking an Object StatusCode sc = m_storeGate setConst(TrkColl);

  5. Retrieving a Data Object • Specifying a Key: DataHandle<TrackCollection> TrkColl; sc = m_storeGate  retrieve( TrkColl, TrkCollName); We create an instance of the DataHandle (TrkColl) and pass it to the retrieve method. It is returned to you and can be used as a C++ pointer: TrkColl  some_method_in_TrackCollection(); Iterate over Tracks in TrackCollection just as you used to. • Retrieving the Default instance: DataHandle<TrackCollection> DefaultTrkColl; sc = m_storeGate  retrieve( DefaultTrkColl);

  6. Retrieving all Data Objects • If you have several TrackCollections recorded in the SG and you wish to retrieve ALL of them, this is what you do: • DataHandle<TrackCollection> dbegin, dend; • m_storegate  retrieve(dbegin, dend); • for (; dbegin != dend; ++ dbegin) // loop over TrackCollections • { • dbegin  method_in_trackCollection(); • TrackCollection::iterator iter dbegin  begin(); • for (; iter != dbegin  end(); ++iter) // loop over TrackObjects • { • (*iter)  TrackPT(); // call some method in Track • } • } • This is not a part of the exercise today, but for your information.

  7. Store Access Policy An object in SG may be modified until it is setConst • Access to a const Data Object: const DataHandle<TrackCollection> trackHandle; m_storegate  retrieve( trackHandle, key ); • Only const methods in the Data Object are accessible! • class Track { void set_pT(float pT) { m_pT = pT; } // NO ACCESS float get_pT const { return m_pT; } // ACCESS OK … } • Must use const-iterators to iterate over TrackCollection • If you do not specify const, this will force a check. If the data object you are accessing is ‘const’, then an error is returned if accessing it in a non-const way.

  8. Tutorial Setup - 1 • We use accounts on atlas.cern.ch (lxplus cluster) • User: atltr<x> where <x> is 0- 9 and a-e • Password: ATLtrain • Machine: atlas.cern.ch • Working directory in students AFS accounts

  9. Tutorial Setup - 2 • Copy CMT requirements file in your home directory (~/requirements) • Already done for you - basic one from Atlas CMT primer • Defines: • Your site • Your software distribution area • The release number of Atlas software • Setup CMT (once if not done already) • sh // CERN tcsh is obsolete and gives problems • source /afs/cern.ch/sw/contrib/CMT/v1r10p20011126/mgr/setup.sh • cmt config • Check g++ -v • We want 2.95.2!

  10. Tutorial Setup - 3 • Go to our work directory • cd maxidisk/Athena // create it if not there • cmt co -r AthExStoreGateExample-00-00-20 Control/AthenaExamples/AthExStoreGateExample • cmt co TestRelease • Go to TestRelease cmt directory • source setup.sh • cmt bro gmake • athena SGTutorial_jobOptions.txt • If using release 3.0.1 you need also to check out • StoreGate-02-00-16

  11. Hands On • In AthExStoreGateExample/[…]/Tutorial, you will find: • Two algorithms: • SGWrite • SGRead • A data object class: MyDataObj • A contained object: MyElement • A object for data links: LinkObj • The ClassDEF macros Tutorial_ClassDEF.h • You do not have to modify any Data classes, • only algorithms, although they are worth a read.

  12. Hands On (contd.) • SGWrite: • Create a MyDataObj(PART 1) • set the data member in MyDataObj • Register MyDataObj using a key • Create a std::vector of MyElement(s)(PART 2) • Create and Fills two MyElement(s) • (new std::vector<MyElement>(2)) • push MyElement(s) into vector • Register key-less (default key) • Create LinkObjand set data link members(PART 3) • Set links to: • MyDataObj • one specific MyElement in the vector collection • SGRead: (PART 1 - PART 3) • Retrieves the objects from the transient store: MyDataObj, MyElement and LinkObj • Interrogates elements and dumps contents on screen.

  13. Hands On (contd.) • Take a look at Tutorial_ClassDEF.h • It contains the CLASS_DEF macros for the “external” data object your package uses (typically the STL containers) In this case we have (omitting namespaces) CLASS_DEF(vector<MyElement, 9903, 1) “9903” is the famous CLID “1” is the version number (currently ignored by SG) • More examples are in ../src/StoreGateExample_ClassDEF.h

  14. Hands On (contd.) • Fill in the algorithms SGWrite and SGRead (PART 1-2) • In SGWrite you need to : • obtain the StoreGateSvc pointer and cache it in initialize() • StatusCode sc = service("StoreGateSvc", p_eventStore); • Record by data type • with a key = (property from jobOptions) • StatusCode sc = p_eventStore->record(pdobj, m_DataObjKey); • without a key • StatusCode sc = p_eventStore->record(pcoll);

  15. Hands On (contd.) • Fill in the algorithms SGWrite and SGRead (PART 1-2) • In SGWrite you need to : • obtain the StoreGateSvc pointer and cache it in initialize() • StatusCode sc = service("StoreGateSvc", p_eventStore); • Record by data type • with a key = (property from jobOptions) • StatusCode sc = p_eventStore->record(pdobj, m_DataObjKey); • without a key • StatusCode sc = p_eventStore->record(pcoll);

  16. Hands On (contd.) • Fill in the algorithms SGRead (PART 1-2) • You need to : • Create a “const” DataHandle and pass it to the retrieve method • Using same key! • const DataHandle<MyDataObj> dobj; • StatusCode sc = m_storeGate->retrieve(dobj, m_DataObjKey); • On return, dobj can be used as a pointer to the DataObject • Retrieve the vector collection • Iterate over the collection to access MyElement(s) • for (std::vector<MyElement>::size_type i=0; i<coll->size(); ++i) • Dump the contents of MyDataObj (PART 1) and MyElement (PART 2). Use the MsgStream.

  17. Hands On (contd.) • From TestRelease/<version>/cmt • cmt broadcast gmake • cd to the run area • Where the jobOption files are • In your jobOptions file, you need to • Declare a string key for data objects in the TS, e.g., SGWrite.DataObjKey = “MyData” • Same for SGRead

  18. Links • Allow to establish a persistable inter objects elationship • A Track holding pointers to a set of associated hits. • A link can be to a single object/collection • DataLink<MyDataObj> m_objLink; • DataLink<MyColl> m_collectionLink; • Or an element in a list/vector (SequenceLink), a map (MapLink) or a set (SetLink) or non-STL container like HepMC • SequenceLink<std::vector<MyElement> >::type m_contLink; • The data link can be used as though it was a pointer to the data object or to the element. To get to the ‘real’ object/element one has to dereference the link • *m_objLink • *m_contLink • Collections must not be modified after a DataLink to an element in the collection has been established.

  19. Creating a DataLink • Example: • Link to a data object m_objLink.toStorableObject(dobj); • Link to a contained object std::vector<MyElement>* pVect; SequenceLink< vector<MyElement> >::type seqLink; seqLink.toContainedElement(*pVect, pElement); • time consuming index search • A faster way: seqLink.toIndexedElement(*pv, index); • index = 0 for first element, 1 for second element, … • Not in 3.0.0: use StoreGate-02-00-16

  20. Hands On • In LinkObj.h: Insert as data members a DataLink to a MyDataObj and a SequenceLink to a MyElement in the vector created in part 2 Implement LinkObj methods using • m_objLink.toStorableObject(dobj); • m_contLink.toContainedElement(coll, cobj); • Or better • m_contLink.toIndexedElement(coll, index); Implement a LinkObj extractor (operator <<) that invokes the linked-to object extractors. For the SequenceLink also print the index value • ost << “ link to MyElement[“ << rhs.m_contLink.index()”] :” • << *rhs.m_contLink;

  21. Hands On #include "StoreGate/DataLink.h" #include "StoreGate/tools/STLlinks.h” #include “Tutorial_ClassDef.h • In SGWrite (Part 3): Instantiate a LinkObj • Establish the data links in LinkObj to MyDataObj and an element within vector<MyElement>. • In SGRead (Part 3): • Retrieve the LinkObj and verify that it has worked. log << MSG::INFO << "retrieved default LinkObj:\n" << *linkObj << endreq;

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