D19287: [ExtractorCollection] Load extractor plugins lazily

[Stefan Brüns]

bruns created this revision.
bruns added reviewers: Baloo, Frameworks, ngraham, astippich, poboiko.
Herald added projects: Frameworks, Baloo.
Herald added a subscriber: kde-frameworks-devel.
bruns requested review of this revision.

REVISION SUMMARY
  In many cases, only a few plugins are required, or even only one
  (e.g. for baloo-widgets, baloo_filemetadata_temp_extractor) or none
  (in case there is no extractor for a given mimetype).
  
  Loading of plugins is somewhat costly, so delay loading of plugins until
  they are requested by fetchExtractors(mimetype).
  
  For e.g. extracting tags from an mp3 file, which only requires the
  taglibextractor, the runtime is reduced by more than 90%.

TEST PLAN
  ctest
  valgrind --tool=callgrind

REPOSITORY
  R286 KFileMetaData

BRANCH
  lazy_loading

REVISION DETAIL
  https://phabricator.kde.org/D19287

AFFECTED FILES
  src/extractor.cpp
  src/extractor.h
  src/extractor_p.h
  src/extractorcollection.cpp
  src/extractorcollection.h

To: bruns, #baloo, #frameworks, ngraham, astippich, poboiko
Cc: kde-frameworks-devel, domson, ashaposhnikov, michaelh, astippich, spoorun, ngraham, bruns, abrahams
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