HTCondorWiki: Class Ad Conversion

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Conversion to New ClassAds

This is part of ticket #187.

Analysis of Condor's use of old ClassAds

Old ClassAd usage summary - A summary of the number of call sites in the Condor code for each Old ClassAds method.
Old ClassAd usage details - Details of the number of call sites in the Condor code for each Old ClassAds method, and where it's called from.
The wiki code for the individual calls is available in /p/condor/workspaces/nleroy/OldClassAdWiki -- the summary and detail files above are in there, as well as the code for each of the above, each in it's own file.

Additional conversion info

Direct use of ExprTree

Many parts of the code do the following to evaluate an expression in the context of a ClassAd:

Parse() to create an ExprTree
ExprTree::EvalTree() to evaluate it against an ad
Examine the resulting ExprResult object

These need to be converted to the following sequence:

ClassAdParser::ParseExpression()
ExprTree::SetParentScope()
ExprTree::Evaluate()
Examine the resulting Value object

This work can probably be done mostly by a student.

ClassAdList

There is no equivalent to the ClassAdList class in new ClassAds. We propose writing a compatibility ClassAdList that's a simple wrapper around an STL vector of ClassAd pointers. We would emulate the interface of the old ClassAdList, but not the reference counting. Nowhere do we put the same ClassAd into multiple ClassAdLists.

In a couple places, we move an ad from one list to another. For these locations, we'll need to add a method to allow movement without deletion.

Meta Operators

In new ClassAds, the meta equality operators are called 'is' and 'isnt'. We are thinking of expanding the new ClassAds parser to recognize the old operators '=?=' and '=!=' and convert them.

STL Exceptions

Do we need to worry about handling exceptions from STL objects?

Chained Ads

New ClassAds support chaining, but the iterators ignore them. The chained ad can be referenced explicitly by callers where it matters.

Warnings

It would be nice to emit warnings whereever the compatibility functions are invoked, so that we don't forget to convert them eventually.

Invisible Attributes

Old ClassAds support the notion of private attributes that can be marked invisible when exporting an ad. The set of invisible attributes is static and invisibility is only done for the put() and dPrint() calls, so we handle this strictly in the compatibility functions.

String Escaping

String escaping is different between new and old ClassAds. We need to ensure that this is handled properly when parsing and unparsing old ClassAd format.