1
Algorithm Toolswhat they are, how to get them
and how to use them

• G.Corti
• 5th Software Week
• 6 July 2000

2
Algorithms and Services

• Algorithms (and sub-Algorithms)
• are initialized and finalized by the framework
• are executed once per event ( sub-algorithms
  depending on the parent algorithm )
• have the lifetime of a job
• request/store/share data in Transient Event Store
• Services
• are used by the algorithms to help perform their
  work
• are setup and initialized at the beginning of a
  job by the framework and used by many algorithms
  as often as necessary
• they do not have a state

3
Simpler algorithms?

• Sometimes in an Algorithm it is necessary to
  execute the same operation more than once per
  event, only for some events, on specific non
  identifiable data objects, producing new objects
  that will be put in the Event Store later
• Vertexing
• Track transport
• Association to truth
• Selection of particles based on a pID CL
• Some Algorithms want to do similar operations but
  with a slightly different configuration, some
  will use a standard configuration
• Idea of Tools and ToolSvc

4
Requirements

• An Algorithm requires a Tool on a per need base
• The ToolSvc checks if the requested type of Tool
  is available and returns an instance of the
  requested type after configuring it
• An Algorithm can have a private instance of a
  Tool that can be configured according to its need
  via JobOptions
• An Algorithm can use a Tool as-it-is, in this
  case the ToolSvc will provide a common Tool
  (shared-Tool)
• An Algorithm should be able to use a Sub-Tool
  without worrying about the implementation
• The ToolSvc keeps track of the Tools instantiated
  and if a tool exists it does not re-create it
• An Algorithm can tell the ToolSvc if it will not
  need a tool anymore
• The ToolSvc will decide which tools instances can
  be deleted (always done at finalization of the
  Service)
• Not only Algorithms would want to use Tools (
  also Services )

5
Tools and ToolSvc diagram
IToolSvc
IAlgTool
IToolFactory
6
IAlgTool

• The IAlgTool interface is implemented by the
  AlgTool base class
• name( )
• stdstring
• the identifying full name of an AlgTool instance
• concatenation of the parent name, a dot, and a
  tool dependent part
• ToolsAnalysisAlgorithm.ImpactPar
• tool dependent part automatically set to type or
  user specified
• type( )
• stdstring
• the type (concrete class) of an AlgTool
• parent ( )
• const IInterface
• the parent of a concrete AlgTool
• can be an algorithm or a service

7
IToolSvc

• The IToolSvc interface is the specific interface
  implemented by the ToolSvc
• retrieveTool (const stdstring type, T tool,
  const IInterface parent0, bool createIftrue )
• StatusCode
• retrieve specified tool sub-type with tool
  dependent part of the name automatically
  assigned
• type, is the AlgTool type
• tool, returned as type requested by the user
• parent, by default no parent
• createIf, flag requesting creation or not if not
  existing, by default created
• retrieveTool (const stdstring type, const
  stdstring name, T tool, const IInterface
  parent0, bool createIftrue )
• as above but with tool dependent part of the name
  specified by the requester as name

8
Some remarks

• An AlgTool does not have an initialize/finalize
  method
• The AlgTool base class has an accessor to the
  ServiceLocator and to the MessageService
• the tool sets them at creation by getting them
  from the parent
• specific services can be retrieved by derived
  tools if necessary
• Common Tool or Private Tool
• Common tools belong to the ToolSvc (when
  parent is not specified)
• the full identifying name is for example
  ToolSvc.ImpactPar
• If a common tool is requested the first request
  will trigger its creation
• Private tool really belong to the parent but the
  parent does not need to keep them

9
...remarks (cont.)

• ToolSvc will hold a tool. At finalization it
  will clean up all the tools.
• Example of how to use tools and some concrete
  implementations of tools in GaudiExamples/ToolsAna
  lysis of next Gaudi release
• There could be GaudiTools, specific applications
  tools (ex. Physics analysis tools, user tools)

10
How to retrieve a tool

• Get the ToolSvc ( as any other service )
• IToolSvc toolsvc 0
• sc serviceLocator()-gtgetService( "ToolSvc",
  IID_IToolSvc,
• (IInterface)( toolsvc
  ))
• at the moment ToolSvc is an ExternalService
• need to request it in the JobOptions
• it is not available in the Algorithm service
  accessor methods
• Retrieve a tool
• ImpactPar impPar
• sc toolsvc-gtretrieveTool("ImpactPar", impPar,
  this )
• if( sc.isFailure() )
• log ltlt MSGFATAL ltlt Unable to create tool" ltlt
  endreq
• return sc
• the algorithm decides when and if to keep it or
  not

11
How to write a concrete tool

• Instantiate a static factory in the
  implementation file
• static ToolFactoryltVertexSmearergt s_factory
• const IToolFactory VertexSmearerFactory
  s_factory
• Inherit from AlgTool base class
• Could have an additional level of inheritance
  with additional interfaces
• Declare in constructor specific properties and
  get services necessary to the implementation
• VertexSmearerVertexSmearer(const stdstring
  type, const stdstring name, const IInterface
  parent) AlgTool( type, name, parent )
• m_randSvc 0
• if( serviceLocator() )
• StatusCode sc serviceLocator()-gtgetService(
  "RndmGenSvc", IID_IRndmGenSvc,
  (IInterface) (m_randSvc) )
• declareProperty("dxVtx", m_dxVtx 9
  micrometer)
• Implement necessary functionality

12
Configure a tool via the jobOptions

• A concrete tool can be configured using the
  jobOptions
• Same convention as for everything else
• IdentifyingNameOfTool.NameOfProperty
• AlgTool base class has the OutputLevel Property
• If not specified in the JobOptions the
  OutputLevel of the parent will be taken
• RecPrimaryVertex.VertexSmearer.OutputLevel 3
• RecPrimaryVertex.VertexSmearer.dxVtx 0.009
• RecPrimaryVertex.VertexSmearer.dyVtx 0.009
• RecPrimaryVertex.VertexSmearer.dzVtx 0.038

13

• First version of the ToolSvc and AlgTool is
  available in GaudiSys v5
• Concrete tools can be implemented and used
• More bookkeeping in the future
• Additional inheritance level with more interfaces
  for general tools to be developed