diff options
author | Igor Kushnir <igorkuo@gmail.com> | 2021-03-29 18:58:19 +0300 |
---|---|---|
committer | Qt Cherry-pick Bot <cherrypick_bot@qt-project.org> | 2021-04-24 12:49:14 +0000 |
commit | 1cb2bb2a28249807b48fc2b4a5995a30eaf69682 (patch) | |
tree | 95fa26b463d600d92efc5488ecc4ef168efc13c6 | |
parent | c0d310d9969111713ec705db1c6c4833c92df468 (diff) |
Optimize quadratic-time insertion in QSortFilterProxyModel
Let N = proxy_to_source.size() before the code modified in this commit.
Let M = (N - proxy_start). Let K = source_items.size(). The algorithmic
complexity of the removed loop is O(N+K+K*M), assuming the number of
O(N+K) reallocations is a constant. The complexity of the QList::insert
and std::copy implementation is O(N+K). This is much faster in practice
when K and M are of the same order of magnitude as N.
For example, this quadratic complexity issue results in noticeable
slowdown in the following scenario:
* a QSortFilterProxyModel is used only for filtering, not sorting;
* first set a filter that matches a single item in the middle of a
huge number of items (about one million) - this is reasonably fast
(takes about a second);
* then clear the filter (i.e. set an empty filter so that no item is
filtered out) and watch your application's UI freeze for a minute.
The "Add QSortFilterProxyModel clear-filter benchmark" commit (with
Change-Id I419a5521dd0be7676fbb09b34b4069d4a76423b1) adds a benchmark
that runs much faster with this performance fix.
Change-Id: Ieaec173e6910f5d21eaee49402087f7711abbedf
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 7d92ef63d7c2d9d017d89905a2ee0d1e9226b15c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
-rw-r--r-- | src/corelib/itemmodels/qsortfilterproxymodel.cpp | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/corelib/itemmodels/qsortfilterproxymodel.cpp b/src/corelib/itemmodels/qsortfilterproxymodel.cpp index 2d52fa9734..2f0df724bc 100644 --- a/src/corelib/itemmodels/qsortfilterproxymodel.cpp +++ b/src/corelib/itemmodels/qsortfilterproxymodel.cpp @@ -837,8 +837,9 @@ void QSortFilterProxyModelPrivate::insert_source_items( q->beginInsertColumns(proxy_parent, proxy_start, proxy_end); } - for (int i = 0; i < source_items.size(); ++i) - proxy_to_source.insert(proxy_start + i, source_items.at(i)); + // TODO: use the range QList::insert() overload once it is implemented (QTBUG-58633). + proxy_to_source.insert(proxy_start, source_items.size(), 0); + std::copy(source_items.cbegin(), source_items.cend(), proxy_to_source.begin() + proxy_start); build_source_to_proxy_mapping(proxy_to_source, source_to_proxy, proxy_start); |