[Differential] [Request, 31 lines] D4362: RFC: [AppletQuickItem] Cache QQmlComponent used for settings QtQuick Controls 1 style

[Kai Uwe Broulik]

broulik created this revision.
broulik added a reviewer: Plasma.
broulik set the repository for this revision to R242 Plasma Framework (Library).
Restricted Application added projects: Plasma, Frameworks.
Restricted Application added subscribers: Frameworks, plasma-devel.

REVISION SUMMARY
  Plasma spends roughly 0.5ms per applet just compiling this component (QQmlComponent creation), so cache it away.
  All applets did share the same QQmlEngine here but I don't think this can be trusted, hence store the components in a QHash per engine.
  While at it, turn the Item into a QtObject to reduce overhead since we just want the Component.onCompleted to be executed and that's it.
  
  Before: 41 calls (18ms in total)
  After: 41 calls (1.9ms in total)

TEST PLAN
  Verified that a QtQuick Controls 1 Button still uses the Plasma theme.
  
  The QObject::destroyed I use to remove the component from the hash again is never executed, even on kquitapp plasmashell.

REPOSITORY
  R242 Plasma Framework (Library)

REVISION DETAIL
  https://phabricator.kde.org/D4362

AFFECTED FILES
  src/plasmaquick/appletquickitem.cpp
  src/plasmaquick/private/appletquickitem_p.h

EMAIL PREFERENCES
  https://phabricator.kde.org/settings/panel/emailpreferences/

To: broulik, #plasma
Cc: plasma-devel, #frameworks, lesliezhai, ali-mohamed, jensreuterberg, abetts, sebas
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