SolrConfig.Initializable: allow configurable class instances to depend on the
SolrCore instance
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Key: SOLR-399
URL: https://issues.apache.org/jira/browse/SOLR-399
Project: Solr
Issue Type: Improvement
Reporter: Henri Biestro
Priority: Minor
Fix For: 1.3
WHAT:
This patch introduces initialization behaviors for instances of configurable
classes.
WHY:
Introduced through solr-215, SolrConfig.Initializable allows some classes
(Tokenizer, Filter) to get access to the SolrConfig at initialization time.
It would be convenient to extend this so that instances of configurable classes
could access objects known by the core - and thus the schema .
see http://www.nabble.com/SolrConfig.Initializable-tf4665036.html
HOW:
SolrConfig is extended to declare some new initialization dedicated interfaces
(Initializable, InitializablePlugin, InitializableBy) that classes wishing to
benefit from the initialization behaviors need to implement.
SolrCore.Initializable interface is also introduced for the same purpose. All
those interfaces require the implementation of some 'init' method.
It is guaranteed that:
1/ SolrConfig.Initializable*.init is called before SolrCore.Initializable.init
2/ SolrCore.Initializable.init is guaranteed to be called only once when it is
successful at core initialization time.
When the core is being initialized, all instances that go through
SolrConfig.initInstance that are SolrCore.Initializable are queued into an
initialization list that guarantees uniqueness (aka they are only queued once).
At the end of core initialization, the solrConfig.init(core) is called; this
triggers the call to SolrCore.Initializable.init(core) for each queued
instances. That method must be implemented to return 'true' if the
initialization has been performed, 'false' if it must be re-evaluated. This
allows one instance to depend on another initialization (a tokenizer could
require a fieldType).
Solrconfig will loop around the queue while it can successfully initialize
instances or new ones are posted; if the loop can not reduce the number of
instances expecting initialization, it is considered an error (and this will
avoid potentially cyclic dependencies).
After the core has been initialized, the SolrConfig will automatically post
instance to the SolrCore queue & empty it right away with the same behavior.
Note that after the core has been initiallized, the SolrConfig is bound to that
core; reusing such a bound SolrConfig for another core will generate an
exception.
USAGE:
Any class that implements one of SolrConfig.Init* interface implements some
'init' method that will be called through SolrConfig.
The sequence of call is:
SolrConfig.Initializable instance = solrConfig.newInstance("name.of.class");
...
solrConfig.initInstance(instance, args);
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