Classified Advertisements (classads) are the lingua franca of Condor. They are used for describing jobs, workstations, and other resources. They are exchanged by Condor processes to schedule jobs. They are logged to files for statistical and debugging purposes. They are used to enquire about current state of the system.
A classad is a mapping from attribute names to expressions.
In the simplest cases, the expressions are simple constants (integer, floating
point, or string). A classad is thus a form of property list.
Attribute expressions can also be more complicated. There is a protocol
for evaluating an attribute expression of a classad vis a vis
another ad. For example, the expression "other.size > 3" in one
ad evaluates to true if the other ad has an attribute named
size and the value of that attribute is (or evaluates to)
an integer greater than three. Two classads match if each ad
has an attribute requirements that evaluates to true
in the context of the other ad. Classad matching is used by the Condor
central manager to determine the compatibility of jobs and
workstations where they may be run.
The classad library is available as a separate stand-alone package for use in applications other than Condor.
If you use the ClassAd library, we encourage you to subscribe to the classad-users mailing list. This list is for discussion among all ClassAd users, and for occasional announcements related to ClassAds. There is a web page for subscribing to the mailing list. At least one of the ClassAd developers reads this mailing list.