[cfe-dev] AST matchers and thread safety

[Jesper Eskilson]

On 09/24/2013 10:41 AM, Gabor Kozar wrote:
> Hi,
> Since the AST should be immutable once created, and AST matchers are 
> only a high-level wrapper for RecursiveASTVisitor, so I'd expect no 
> problems with multithreading. This definitely needs to be confirmed 
> though by someone who actually knows what they are talking about. :)
> Just out of curiosity, what is your use case? Navigating the AST is 
> fast, especially compared to the cost of building the AST. Are you 
> running a huge number of matchers?

I have a legacy C++ code base which I'm trying to extract useful 
information out of. For example, a single matcher which matches all 
method definitions of a particular class takes around 8 seconds on my 
machine, varying a little with the complexity of the matcher.

Is the AST kept around for the lifetime of the "ClangTool" object, or is 
it recreated each time the "run" method is invoked? Some of my matchers 
depend on information gathered by other matchers  (one matcher gathers 
method definitions so they can be consumed by when matching the 
corresponding class declarations). For example:

MatchCallback cb1, cb2;
MatchFinder finder1

finder1.addMatcher(m1, &cb1);
finder1.addMatcher(m2, &cb2);

tool->run(newFrontendActionFactory(&finder1));

MatchCallback cb3, cb4;
MatchFinder finder2

finder2.addMatcher(m3, &cb3);
finder2.addMatcher(m4, &cb4);

tool->run(newFrontendActionFactory(&finder2));

Will this build the AST twice or just once?  Is there any guarantee 
concerning the order in which the matcher callbacks are invoked?

> -- 
> Gábor Kozár -- ShdNx
> kozargabor at gmail.com
> On Tue, Sep 24, 2013, at 10:15, Jesper Eskilson wrote:
>> Hi,
>> Are the AST matchers thread safe? I have a bunch of matchers which I
>> would like to run in separate threads for performance reasons. Is that
>> expected to work, or am I overly optimistic?
>> /Jesper
>> -- 
>> *Jesper Eskilson* /Development Engineer/
>> IAR Systems AB
>> Box 23051, Strandbodgatan 1
>> SE-750 23 Uppsala, SWEDEN
>> E-mail: jesper.eskilson at iar.com <mailto:jesper.eskilson at iar.com> 
>> <mailto:jesper.eskilson at iar.com>
>> Website: www.iar.com
>> <http://www.iar.com> Twitter: www.twitter.com/iarsystems
>> <http://www.twitter.com/iarsystems>
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-- 
*Jesper Eskilson* /Development Engineer/
IAR Systems AB
Box 23051, Strandbodgatan 1
SE-750 23 Uppsala, SWEDEN
E-mail: jesper.eskilson at iar.com <mailto:jesper.eskilson at iar.com> 
Website: www.iar.com
<http://www.iar.com> Twitter: www.twitter.com/iarsystems 
<http://www.twitter.com/iarsystems>