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From Chris Lamprecht <clampre...@gmail.com>
Subject Re: QueryParser not thread-safe
Date Wed, 24 Aug 2005 10:20:26 GMT
I would just create a new QueryParser for each query.  Allocating
short-lived objects is just about free in java, and the time spent
performing the actual search will by far dominate any time spent
constructing QueryParser objects.

On 8/24/05, Vanlerberghe, Luc <Luc.Vanlerberghe@bvdep.com> wrote:
> Thanks for pointing that out!
> I checked the source and QueryParser is indeed not thread-safe (the
> presence of local variables like jj_lastpos that are used *during* the
> parsing makes this obvious)
> 
> Perhaps it should be explicitly mentioned in the javadoc.
> 
> The solution I'll probably go for is using ThreadLocal variables
> (available since jdk 1.2, but there was a problem in the sun jvm with
> deallocation when threads stop until jdk 1.4 or so)
> 
> an example (not compiled, nor tested):
> 
> public class MyQueryFactory {
>    public Query createQuery(String expression) {
>        return threadLocalQueryParser.get().parse(expression);
>    }
> 
>    private ThreadLocal<QueryParser> threadLocalQueryParser=new
> ThreadLocal<QueryParser>() {
>        protected QueryParser initialValue() {
>            return new QueryParser("defaultField", new MyAnalyzer());
>        }
>    };
> }
> 
> (I used jdk 1.5 generics because the code is clearer, remove the
> <QueryParser> and put a few casts where needed if you want this in 1.4
> or lower)
> 
> initialValue() will be only be called once for every thread that calls
> threadLocalQueryParser.get().
> 
> See the javadoc for java.lang.ThreadLocal
> 
> Luc
> 
> 
> -----Original Message-----
> From: jian chen [mailto:chenjian1227@gmail.com]
> Sent: dinsdag 23 augustus 2005 21:38
> To: java-user@lucene.apache.org
> Subject: Re: QueryParser not thread-safe
> 
> Right. My philosophy is that, make it work, then, make it better.
> 
> Don't waste time on something that you are not sure if it would cause
> performance problem.
> 
> Jian
> 
> On 8/23/05, Paul Elschot <paul.elschot@xs4all.nl> wrote:
> > On Tuesday 23 August 2005 19:01, Miles Barr wrote:
> > > On Tue, 2005-08-23 at 13:47 -0300, jhandl@fibertel.com.ar wrote:
> > > > Hi! I've been having problems with lucene's QueryParser,
> apparently it is
> > not thread-safe.
> > > >
> > > > That means I can't parse queries in threads where the queryparser
> object
> > is created once and reused for each query. If I do, the resulting
> queries may
> > have all kinds of weird problems, for example missing terms, duplicate
> terms,
> > etc.
> > > >
> > > > I don't like the idea of creating a new queryparser for each
> query, so I
> > am looking for alternatives. Any ideas?
> > >
> > > Using a non-threadsafe object in a threaded environment is fairly
> > > standard in Java, just wrap it in a synchronized block.
> > >
> > > If you don't want all threads waiting on one query parser, create a
> pool
> > > of them.
> >
> > Or use one parser per thread.
> >
> > Regards,
> > Paul Elschot
> >
> >
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> >
> >
> 
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> 
> 
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