A. Running Multiple Instances of ACIS Extract

When your project involves several ACIS observations and you have a computer with several CPUs, a lot of time can be saved by running multiple instances of AE in parallel, each in its own IDL session. The speedup you will achieve depends on many factors, and on the stage of AE (since some stages are CPU-limited and some stages are filesystem-limited).

AE takes the following precautions to help support multiple instances running simultaneously:

CIAO and HEASOFT

The CIAO and HEASOFT packages do NOT nominally support running multiple instances of the same tool. The problem is that tools write to the user's parameter files, pointed to by the environment variable $PFILES. To avoid parameter file conflicts among multiple instances of any CIAO or HEASOFT tool, AE creates a scratch directory for parameter files and configures the environment variable PFILES to look for parameter files in the following paths:

• the scratch directory
• $ASCDS_INSTALL/contrib/param/
• $ASCDS_INSTALL/param/
• $HEASOFT/syspfiles

The value of PFILES inherited from the observer is ignored. Thus the user is freed from confusing and error-prone manipulations of the PFILES environment variable. The one parameter file which must contain observation-specific information, ardlib.par, is explicitly provided to AE by the observer in the EXTRACT_SPECTRA stage (§E.3).

AE Scratch Files

The scratch files used by AE are placed in a uniquely named scratch directory (/tmp/AExxxx.noindex/) to avoid conflict with other running AE sessions.

Lock Files

In the FIT_SPECTRA stage lock files are used to prevent multiple instances of XSPEC running on the same source.

The one known opportunity for conflict between multiple instances of AE is the */<ObsId>/obs.stats FITS files where various source properties are stored by several AE stages. The EXTRACT_EVENTS, EXTRACT_SPECTRA, TIMING, and EXTRACT_BACKGROUNDS stages all write to these files. Thus it is not completely safe to run these stages simultaneously for the same observation. AE sessions processing different observations should run correctly.

As shown in Appendix D, the AE recipe tools write to the obsXXXX directories in the standard AE directory tree. Thus obsXXXX directories must not be shared among multiple projects.