6.3. The event logger and ReadoutShell

The Readout GUI works with the event logger to maintain a directory structure of event files and associated data. You can associate an arbitrary set of files and directory subtrees with each run. Through heavy use of symbolic links, the Readout GUI provides you with two views of your data.

Events view. The events view presents all of the event files in a single directory. This view allows you to sequentially analyze several runs without needing to move around in the directory hierarchy.

Runs view. This view collects all of the data associated with each run into a single directory.

The top of the directory subtree that is managed by Readout Gui is determined by a symbolic link; ~/stagearea. [1] This must be created by you when you set the account up for data taking and should point to the event area that you were assigned.

When Readout GUI runs the first time it will create the directory structure it need underneath the directory pointed to by ~/stagearea.

The directory tree created looks like this:

Figure 6-4. Readout GUI Directory tree

stagearea +
          +----> experiment+
          |                +---> current
          |                +---> run1
          |                +---> run2
          ...             ...
          +----> complete
          +----> current

Let's start with the ~/stagearea/current directory. The Readout GUI arranges for the event file set currently being accumulated to be written in this directory. Event files have the name run-nnnn-ss.evt where nnnn is a zero filled run number (e.g. 0001), and ss is a zero filled event segment.

The event data from each run are segmented into files that are no more than 2GBytes long. The segments number from 00. Segmenting runs into file that are no larger than 2Gbytes avoids problems with file size limitations on some types of file systems.

The ~/stagearea/experiment subdirectory tree provides the run view of the data. Within that directory are subdirectories for each recorded run. At the end of a run, the Readout GUI moves the event data files from the ~/stagearea/current directory into the associated run directory. The data in ~stagearea/experiment/current is copied into the run directory as well. Files or directories pointed to by symoblic links in the experiment/current subtree are copied rather than the links themselves.

Finally, the complete directory provides the events view of the experiment. At the end of a run, after the event file segments copied to ~stagearea/experiment/runn, a symbolic link to each event file segment is created here.



Environment variables can override this link however and are useful in the event you are using a single account to do multiple tests for which you want to segregate the data.