Optimize KConfigGroup::exists and similar operations.

Review Request #118586 - Created June 6, 2014 and submitted

Information
Milian Wolff
kdelibs
master
Reviewers
kdelibs
dfaure, mdawson, ossi
Optimize KConfigGroup::exists and similar operations.

Before, these kind of read-only operations did a lot of allocations:

1) allocate a list of all sub groups
2) for the above, also allocate a sub-group match key
3) iterate over sub groups, allocate a list of all keys in there
and then finally check whether that list is non-empty

All of the above is now done without a single allocation, by simply
iterating over the list of entries.

Note: The whole list was iterated even before in allSubGroups. Now
we still do that, but check for non-empty keys in the group or
sub group directly. Much more efficient.

Note2: While at it, allSubGroups is also optimized to not require the
allocation of the subgroup match key.
The unit tests all run just fine. I broke it while implementing this patch, so I'm confident this functionality is actually properly tested and covered :)

The saved allocations are plenty. This is e.g. from the startup of kwrite:

2844 allocations at:
0x7ff7fbc490e9 QHashData::allocateNode(int) /usr/lib/libQtCore.so.4
0x7ff7fc152f8e QHash<QString, QHashDummyValue>::createNode(unsigned int, QString const&, QHashDummyValue const&, QHashNode<QString, QHashDumm
yValue>**) in /usr/include/qt4/QtCore/qhash.h:543 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc152472 QHash<QString, QHashDummyValue>::insert(QString const&, QHashDummyValue const&) in /usr/include/qt4/QtCore/qhash.h:763 /ssd/mi
lian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc1515f9 QSet<QString>::insert(QString const&) in /usr/include/qt4/QtCore/qset.h:181 /ssd/milian/projects/compiled/kde4/lib/libkdecore.
so.5
0x7ff7fc1501ab QSet<QString>::operator<<(QString const&) in /usr/include/qt4/QtCore/qset.h:201 /ssd/milian/projects/compiled/kde4/lib/libkdec
ore.so.5
0x7ff7fc14b4a7 KConfigPrivate::keyListImpl(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:367 /ssd/
milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc14b25d KConfigPrivate::hasNonDeletedEntries(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:
347 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc14dfeb KConfig::hasGroupImpl(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:856 /ssd/milian
/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc1536b4 KConfigBase::hasGroup(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfigbase.cpp:42 /ssd/mil
ian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc158fcd KConfigGroup::exists() const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfiggroup.cpp:592 /ssd/milian/projects/com
piled/kde4/lib/libkdecore.so.5

2844 allocations at:
0x7ff7fbc71426 QString::QString(int, Qt::Initialization) /usr/lib/libQtCore.so.4
0x7ff7fbd66820 ? /usr/lib/libQtCore.so.4
0x7ff7fbc737db QString::fromUtf8(char const*, int) /usr/lib/libQtCore.so.4
0x7ff7fc14b494 KConfigPrivate::keyListImpl(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:367 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc14b25d KConfigPrivate::hasNonDeletedEntries(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:347 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc14dfeb KConfig::hasGroupImpl(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfig.cpp:856 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc1536b4 KConfigBase::hasGroup(QByteArray const&) const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfigbase.cpp:42 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5
0x7ff7fc158fcd KConfigGroup::exists() const in /ssd/milian/projects/kde4/kdelibs/kdecore/config/kconfiggroup.cpp:592 /ssd/milian/projects/compiled/kde4/lib/libkdecore.so.5

All of these are gone with the patch.

Issues

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Description From Last Updated
David Faure
Milian Wolff
Milian Wolff
Oswald Buddenhagen
Commit Hook
Commit Hook
This review has been submitted with commit 9a5d6523689067a9cde717a8f375d4eca246b119 by Milian Wolff to branch master.
Milian Wolff
Review request changed

Status: Closed (submitted)

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