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From "Uwe Schindler (JIRA)" <>
Subject [jira] Commented: (LUCENE-1693) AttributeSource/TokenStream API improvements
Date Fri, 24 Jul 2009 08:00:19 GMT


Uwe Schindler commented on LUCENE-1693:

And in 3.0 all my phantastic backwards-compatibility stuff is completely removed - and incrementToken()
is abstract - What a pity :( The default impl in incrementToken and all other code parts in will be removed (this is why also new code parts are marked deprectated,
it makes it easier to be removed). The code will be about 1/3 of the current size when the
backwards layer is removed :-)
The biggest problem of the migration to the new API is the backwards stuff, because we have
now 3 different TokenStream APIs (next(), next(Token), incrementToken()). Also TokenWrapper
is backwards stuff and will be removed.

> AttributeSource/TokenStream API improvements
> --------------------------------------------
>                 Key: LUCENE-1693
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 2.9
>         Attachments: lucene-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch,
lucene-1693.patch, LUCENE-1693.patch, lucene-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch,
LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch,
LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, LUCENE-1693.patch, lucene-1693.patch,,,,,,
> This patch makes the following improvements to AttributeSource and
> TokenStream/Filter:
> - introduces interfaces for all Attributes. The corresponding
>   implementations have the postfix 'Impl', e.g. TermAttribute and
>   TermAttributeImpl. AttributeSource now has a factory for creating
>   the Attribute instances; the default implementation looks for
>   implementing classes with the postfix 'Impl'. Token now implements
>   all 6 TokenAttribute interfaces.
> - new method added to AttributeSource:
>   addAttributeImpl(AttributeImpl). Using reflection it walks up in the
>   class hierarchy of the passed in object and finds all interfaces
>   that the class or superclasses implement and that extend the
>   Attribute interface. It then adds the interface->instance mappings
>   to the attribute map for each of the found interfaces.
> - removes the set/getUseNewAPI() methods (including the standard
>   ones). Instead it is now enough to only implement the new API,
>   if one old TokenStream implements still the old API (next()/next(Token)),
>   it is wrapped automatically. The delegation path is determined via
>   reflection (the patch determines, which of the three methods was
>   overridden).
> - Token is no longer deprecated, instead it implements all 6 standard
>   token interfaces (see above). The wrapper for next() and next(Token)
>   uses this, to automatically map all attribute interfaces to one
>   TokenWrapper instance (implementing all 6 interfaces), that contains
>   a Token instance. next() and next(Token) exchange the inner Token
>   instance as needed. For the new incrementToken(), only one
>   TokenWrapper instance is visible, delegating to the currect reusable
>   Token. This API also preserves custom Token subclasses, that maybe
>   created by very special token streams (see example in Backwards-Test).
> - AttributeImpl now has a default implementation of toString that uses
>   reflection to print out the values of the attributes in a default
>   formatting. This makes it a bit easier to implement AttributeImpl,
>   because toString() was declared abstract before.
> - Cloning is now done much more efficiently in
>   captureState. The method figures out which unique AttributeImpl
>   instances are contained as values in the attributes map, because
>   those are the ones that need to be cloned. It creates a single
>   linked list that supports deep cloning (in the inner class
>   AttributeSource.State). AttributeSource keeps track of when this
>   state changes, i.e. whenever new attributes are added to the
>   AttributeSource. Only in that case will captureState recompute the
>   state, otherwise it will simply clone the precomputed state and
>   return the clone. restoreState(AttributeSource.State) walks the
>   linked list and uses the copyTo() method of AttributeImpl to copy
>   all values over into the attribute that the source stream
>   (e.g. SinkTokenizer) uses. 
> - Tee- and SinkTokenizer were deprecated, because they use
> Token instances for caching. This is not compatible to the new API
> using AttributeSource.State objects. You can still use the old
> deprecated ones, but new features provided by new Attribute types
> may get lost in the chain. A replacement is a new TeeSinkTokenFilter,
> which has a factory to create new Sink instances, that have compatible
> attributes. Sink instances created by one Tee can also be added to
> another Tee, as long as the attribute implementations are compatible
> (it is not possible to add a sink from a tee using one Token instance
> to a tee using the six separate attribute impls). In this case UOE is thrown.
> The cloning performance can be greatly improved if not multiple
> AttributeImpl instances are used in one TokenStream. A user can
> e.g. simply add a Token instance to the stream instead of the individual
> attributes. Or the user could implement a subclass of AttributeImpl that
> implements exactly the Attribute interfaces needed. I think this
> should be considered an expert API (addAttributeImpl), as this manual
> optimization is only needed if cloning performance is crucial. I ran
> some quick performance tests using Tee/Sink tokenizers (which do
> cloning) and the performance was roughly 20% faster with the new
> API. I'll run some more performance tests and post more numbers then.
> Note also that when we add serialization to the Attributes, e.g. for
> supporting storing serialized TokenStreams in the index, then the
> serialization should benefit even significantly more from the new API
> than cloning. 
> This issue contains one backwards-compatibility break:
> TokenStreams/Filters/Tokenizers should normally be final
> (see LUCENE-1753 for the explaination). Some of these core classes are 
> not final and so one could override the next() or next(Token) methods.
> In this case, the backwards-wrapper would automatically use
> incrementToken(), because it is implemented, so the overridden
> method is never called. To prevent users from errors not visible
> during compilation or testing (the streams just behave wrong),
> this patch makes all implementation methods final
> (next(), next(Token), incrementToken()), whenever the class
> itsself is not final. This is a BW break, but users will clearly see,
> that they have done something unsupoorted and should better
> create a custom TokenFilter with their additional implementation
> (instead of extending a core implementation).
> For further changing contrib token streams the following procedere should be used:
>     *  rewrite and replace next(Token)/next() implementations by new API
>     * if the class is final, no next(Token)/next() methods needed (must be removed!!!)
>     * if the class is non-final add the following methods to the class:
> {code:java}
>       /** @deprecated Will be removed in Lucene 3.0. This method is final, as it should
>        * not be overridden. Delegates to the backwards compatibility layer. */
>       public final Token next(final Token reusableToken) throws {
>         return;
>       }
>       /** @deprecated Will be removed in Lucene 3.0. This method is final, as it should
>        * not be overridden. Delegates to the backwards compatibility layer. */
>       public final Token next() throws {
>         return;
>       }
> {code}
> Also the incrementToken() method must be final in this case
> (and the new method end() of LUCENE-1448)

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