Last Modified: 25-Oct-1998
Reviewed: 29-Oct-1998

Application Manager (ApplicationMgr)

Purpose and Functionality

The main purpose of the Application Manager (ApplicationMgr) is to steer any data processing application. This includes all data processing applications for LHCb data in all stages: simulation, reconstruction, analysis, high level triggers, etc. Specific implementations of the ApplicationMgr will be developed  to cope with the different environments (on-line, off-line, interactive, batch, etc.). The ApplicationMgr implements the following functionality:

• The event loop. For traditional batch processing applications it implements the so called "event loop". It initializes all the components and services of the application. In particular it initializes the event selector component with a selection criteria for the current job (which events need to be processed). After that, it requests the processing services of all  the relevant processing elements (algorithms) for each event. Finally, it informs all the components when the job is done to allow them to perform the necessary actions at the end of job (saving histograms, job statistics, etc.).
• Bootstrapping the application. The ApplicationMgr is in charge of creating all the services and processing components (algorithms) needed to provide the desired functionality. The concrete type of those components depending on the persistent object store, user interface system, etc. is selected at run time based on the job options.
• Information center. It maintains a directory of the major services and algorithms which have been created by him. It allows other components to locate the requested service based on a name.

Interfaces

The ApplicationMgr provides the following interfaces:

• Service locator. Algorithms and services may ask the ApplicationMgr for references to existing services on the application. For example, to get a reference to the MessageService which is needed by the Algorithm in order to output an error message.
• UserInterface interface. Interface to the user interface to allow the user to interact with the application. This interface is necessary for non-batch oriented applications.

Dependencies

The ApplicationMgr depends on the following services provided by other components of the architecture:

• JobOptionsServer. The JobOptions service provides to the ApplicationMgr the new values for the its properties in case the user would like to overwrite the default ones. These properties may driven the choice of the persistent mechanism, the algorithms which need to be instantiated, the output stream for error messages, etc.
• MessageService. The ApplicationMgr uses the MessageService to report errors and informational messages to the end user.
• AlgorithmFactory. The ApplicationMgr uses the AlgorithmFactory service to create (instantiated) the concrete implementations of the algorithm. In that way, the ApplicationMgr do not need to be changed when new algorithms are introduced into the system.
• Algorithms. Algorithms do the real physics data processing work. Without them the application will not produce any results.
• Other services like PersistecySvc, EventSelector, etc. are  initialized by the ApplicationMgr in order to provide the correct functionality for the specific type of job.