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From Chris Hostetter <>
Subject Re: Proposed extension to SearchHandler / SearchComponent in Solr
Date Mon, 28 Mar 2016 22:52:38 GMT

: Recently I was writing a SearchComponent which works only in a distributed
: context. In the prepare method it alters some static state, and then
: reverts that modification during one of the calls to finishStage. However,
: I realized that if an exception is thrown by another SearchComponent, the
: change is never reverted and my state becomes "corrupted" and doesn't
: reflect the reality.
: To solve this, I thought about adding an "onException" method to the
: SearchComponent class, and make appropriate modifications in SearchHandler
: to support it. Such a change would allow SearchComponent to clean up after
: themselves in a case of exceptions. What do you think?

you really, REALLY, don't want to be modifying static state in a 
SearchCOmponent or RequestHandler -- not "java definition of static 
variable" or even "object instance variable state" on the 
components/handlers themselves.

SearchComponent and RequestHandler instances are re-used 
in parallel threads processing concurrent requests -- so any "state" you 
mutate on them will poluate the results of other requests happening at the 
same time.

If you have state you want to track between prepare/process/finishStage 
you should absolutely use the ResponseBuilder and/or 
SolrQueryRequest for this.

SolrQueryRequest.getContext() exists explicitly for third-party custom 
plugins to track state like you're describing.


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