File Search Paths

• Introduction
• The search path for FHiCL files: FHICL_FILE_PATH
• The search path for many other files: MU2E_SEARCH_PATH

Introduction

What happens if the file is present at more than one place on the list? The list is ordered and the code declares success on the first match; it never looks to see if there is more than one match.

If the code cannot find a match, it throws.

A search path is specified in an environment variable as colon separated list of directories. This is in the same spirit as the well known environment variables PATH, LD_LIBRARY_PATH and PRODUCTS.

The search algorithm treats absolute paths specially. The code can be configured so that, for absolute paths, it ignores the search path and simply looks to see if there is a file at the absolute path. If there is no such file, it throws. Alternatively it can be configured to disallow absolute paths and to only look for files relative to the search path; in this case it throws as soon as it sees an absolute path. This last feature is useful when the program is being used to in production runs for which it is important to maintain a strict audit trail. Mu2e Offline is normally configured to disallow absolute paths; this is to make sure that we do not have a lot of work to do when we start production.

The search algorithm can also be configured to treat paths with a leading "." with the same rules as apply to absolute paths.

Both tools have the same policy, that the file must be found exactly by adding the requested relative path onto each element of the search path. Suppose that we wisht to specify a file:

  /A/B/C/D/E/F.txt

  export MU2E_FILE_PATH=/A/B/I/:/A/G/I:/A/B/C

  export MU2E_FILE_PATH=/A/B/I/:/A/G/I:/A/B/C/D/E

Three important files are not covered by this policy: event-data input files, event-data output files and the root file managed by the TFileService. These files are managed by other facilties which allow only two options: an absolute path or a path that is relative to the current working directory at the time of execution.

FHICL_FILE_PATH

export FHICL_FILE_PATH=.:fcl;

export FHICL_FILE_PATH=$MU2E_BASE_RELEASE:$MU2E_BASE_RELEASE/fcl

export FHICL_FILE_PATH=$MU2E_SATELLITE_RELEASE:$MU2E_SATELLITE_RELEASE/fcl:$FHICL_FILE_PATH

There are two FHiCL prolog files that are included in many .fcl files:

#include "minimalMessageService.fcl"
#include "standardProducers.fcl"

As we get experience with FHiCL we will consider adjustments to these policies. The policies will be as open as possible during our development phase, with the constraint that we understand how to ensure a strict audit trail when the time comes for large scale production.

MU2E_SEARCH_PATH

Starting with version v1_0_0, the class that supports this functionality is Mu2eUtilities/inc/ConfigFileLookupPolicy.hh; under the covers it uses technology from cetlib. Throughout the Mu2e Offline documentation, we will refer to this functionality as "the file lookup policy". This feature is used in:

1. Any file that is parsed by SimpleConfig. This includes:
   • The geometry file, read by the GeometryService.
   • The event generator run-time configuration file, read by the EventGenerator module.
   • The conditions data run-time configuration file, read by the ConditionsService.
   • Any files included into the above three files using #include.
2. The magnetic field maps, read by the BFieldManagerMaker.
3. The particle data table files, read by the ParticleDataTable class.
4. The G4 macro file optionally read by G4_plugin.cc
5. The beam arrival time distribution read by FoilParticleGenerator. ( This should be moved into the conditions service ).
6. Input particles in G4beamline format, read using EventGenerator/inc/FromG4BLFile.hh

In older versions of the code ( v0_3_4 and earlier ) a similar functionality was supported using a different class, FileInPath.

In the following, it is presumed that the reader is familiar with the ideas of base releases and test releases. The environment variable MU2E_SEARCH_PATH is built at two places in the Mu2e setup scripts. In Offline/setup.sh it is set to

export MU2E_SEARCH_PATH=$MU2E_BASE_RELEASE:$MU2E_DATA_PATH;

In Offline/bin/addlocal.sh the environment variable is set to

export MU2E_SEARCH_PATH=$MU2E_TEST_RELEASE:$MU2E_BASE_RELEASE:$MU2E_DATA_PATH;

We are considering replacing the files parsed with SimpleConfig with FHiCL format files because the grouping of parameters will be enforced by the language and not just by convention.

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