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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. We can also write compatibility versions of Parse() and EvalTree().
In new ClassAds, there is no assignment operator inside an ExprTree. A ClassAd contains a list of attribute name and ExprTree pairs. Any code in Condor that's directly inserting or extracting ExprTree's from a ClassAd will need to be updated.
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 (matchmaker.cpp and condor_query.cpp), we move an ad from one list to another. For these locations, we'll need to add a method to allow movement without deletion.
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.
With a couple minor tweaks, the compatibility functions will use the old ClassAd escaping rules. The new parser would continue to use the new escaping rules. We'll have to be careful when changing existing code to call the new methods, especially when parsing expressions taken from a user.
String Classes
New ClassAds use std::string while old ClassAds use MyString. The compatibility functions can accept MyString where appropriate. But as new code is written or old code is converted, they will have to start using std::string.